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Who wants to be a contestant on today's "Is it the BCM or the PCM" show?

2340 Views 49 Replies 6 Participants Last post by  r4nd4llm4n, 
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So I've had a few posts about some electrical gremlins of late. I finally got some codes that stuck, and I finally tracked down a real code reader, and I have the following from what is being reported as the ABS System (Antilock brakes...Hmm). Now my voltage is just upward of 15VDC on the EVIC, and high 14's measured on an actual voltmeter and on an el-cheapo tablet-like scope. I have some questions/comments inline if anyone wants to hazard an answer/response :)

C2101-17 - Battery Voltage Too High - Current Voltage Above Threshold (Is this literally the battery and only the battery, not the alternator?)
C212A-17 - System Voltage - Circuit Voltage Above Threshold (This feels like it would be the alternator/charging system as well as the battery. Whatever voltage was on the circuit feeding the thing that was reporting the fault?)
U0100-00 - Lost Communication With ECM/PCM (Maybe this is the indicator that it's the PCM?)
U0402-00 - Implausible Data Received from TCM (Just how implausible. 600 horsepower is fairly implausible for a 5.7L R/T stock. Of course "Hello, World" is also implausible as is a binary encoded version of Macbeth.)
U0401-00 - Implausible Data Received from ECM/PCM (This also points to maybe the PCM?)
U0403-00 - Implausible Data Received from T-Case (Same as U0402-00)
C121C-00 - Torque Request Signal Denied (oof, DENIED)

Who wants to venture a guess as to what's busted? Is it the PCM? The BCM? Or is a CAN bus toasty/shorted/grounded either in wiring or in some busted controller? My other, previously mentioned symptoms are the persistent battery idiot light and the persistent "low voltage" notice on the EVIC. When we were reading codes, the EVIC displayed the oft-seen "Service Shifter" notice. Also often, the windshield wipers (front) will make a few passes and then stop. Formerly, there were some intermittent headlights coupled with intermittent dashboard display and intermittent Radio/HVAC events (basically seemed like the truck was going to reboot) which happened most often during high throttle situations (I'm like 550+ AWHP. not sure exactly where it's at these days. It's not a LOT of power, but its a lot more power than stock lol). I should probably add that this all started shortly after I suffered like a 2 or 3 day outage of the entire center stack as well as the power door locks and windows on the driver's side and the seat. There were some other things like the passenger door locks, but that window worked (From the passenger door). After doing a battery removal/circuit discharge, it was still not working for a few days. It just started working one day, but after this I'd somehow lost either the gear or actuator on the driver's side hvac damper or the control thereof. Shortly thereafter, these gremlins started, so the first steps were removing the battery, having it test "Charge, Good" but being OEM and 9 years old, replacing it anyway with a DIe Hard Platinum AGM h7. Finally, I did remove and replace the center console and the associated connections, checking each of the 2 ground straps and the connectors themselves for any issues based on the whole BCM being back there and the Service Shifter warnings as well as other threads on this forum showing this type of thing.

That bit about the AC damper door actuator seems unrelated, but is it?

The driver's side vents only blow hot air. The passengers are fine as is the rear. Maybe if I check the condition of the driver's side actuator and gear (sigh its hard to extract due to the torx bit and the clearance from what I see on youtube), I can perhaps identify if there is fault in the BCM since I presume that servo is under the jurisdiction of the BCM and solely the BCM? Or is there some HVAC controller that's separate (and not reporting a code?).

Finally, PCM or a BCM replacement, those are both going to require dealer assistance to stamp my VIN into the device, right? I also, obviously, have a custom tune, and the truck may not even run at all or may self-destruct the engine with a factory tune. It's got a supercharger and injectors and a 6.4L block with 9.5:1 pistons. Who knows what a stock fuel map would do to the engine? But I believe I'd have to flash my junk back to stock so that the diablosport intune can pair up with the replacement PCM. Then I have take a new original backup and get my tuner to re-apply the customizations to that new base/stock tune. Or will the currently loaded tunes still be valid and effective to flash on the replacement PCM? Hell, am I going to have issues with revisions of the PCM and tunability? II think wasn't 2014 the last year not to require unlocking the PCM to tune?

Sigh, thanks in advance for any feedback, input, or questions.
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So do these numbers from the Intelligent Battery Sensor look sub-awesomal... Unrelatedly, I love the typo on the line where Intelligent is misspelled. Actually, that seems silly that there would be software that would mispell something that seems like it ought to be prefix variable.. Does the wording from from AlfaOBD or? I guess this is the BCM so there's no puppeted/subordinate controller that I am aware of (on the CAN bus?) from which this data is scraped/calculated. Either way, that by itself strange but probably not related to my problem with the persisted battery indicator on the dashboard/evic message about low voltage.

And beyond that, why am I now at 79% state of charge? This may also point at an alternator problem, though I am not a fan of that theory because I took the PCM's active generator data for a bit of a ride and it seemed to be A-OK too.

Intelligent Battery Sensor(IBS) Data 1:
Intelligent Battery Sensor Measured Voltage: 12.44 V
Intelligent Battery Sensor Current Range Sensor Setting: 200
Intelligent Battery Sensor Current: -14.00 A
Intelligent Battery Sensor Temperature: 7 °C
Intelligent Battery Sensor Quiescent Current: 0.26 A
Intelligent Battery Sensor Current Error: No error
Intelligent Battery Sensor Temperature Error: No error
Inteligent Battery Sensor Error in Calibration Data: No
Intelligent Battery Sensor Error in ECU Identification: No
Intelligent Battery Sensor Error in NVM Data: No
Intelligent Battery Sensor Response Error: No
Intelligent Battery Sensor (IBS) Data 2:
Intelligent Battery Sensor State of Charge: 79 %
Intelligent Battery Sensor Residual Battery Charge: 28.50 A/h
Intelligent Battery Sensor Predicted Voltage after Cranking: 9.69 V
Intelligent Battery Sensor State of Health: 75.00 A/h
Intelligent Battery Sensor Predicted Time Limit for Start Capability: 155 min
Intelligent Battery Sensor SOC Accuracy Status: Error < 10%
Intelligent Battery Sensor SOF_Q Accuracy Status: Error < 10%
Intelligent Battery Sensor SOF_V Accuracy Status: Error < 10%
Intelligent Battery Sensor SOH_Q Accuracy Status: Error > 15%
Intelligent Battery Sensor SOF_T Accuracy Status: Error < 10%
Intelligent Battery Sensor Blind Charging Flag: Not set
Intelligent Battery Sensor Battery Disconnection Flag: Not set
Intelligent Battery Sensor (IBS) Data 3:
Intelligent Battery Sensor Lifetime Charge Received: 101.13 A/h
Intelligent Battery Sensor Lifetime Charge Released: 100.75 A/h
Intelligent Battery Sensor Voltage Before LIN Wakeup: 10.23 V
Intelligent Battery Sensor Wake Up Reason: Charge current limit detected
Intelligent Battery Sensor (IBS) Data 4:
Intelligent Battery Sensor Calculated Battery Resistance: 0.02 Ohm
Intelligent Battery Sensor Resistance at 100 % SOC and 25 Deg.C: 0.02 Ohm
Intelligent Battery Sensor Accumulated Time Since Last Reset: 1116 sec
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So I'm at. a total loss at this point, no idea where to go next...

  • I've cleared all of the old codes in all of the relevant modules
  • I've had the battery tested both by AutoZone and Advance Auto Parts - good - AAP's tester even stated that it could pull > 1000CCA from the 850CCA battery
  • I've had the alternator "tested" both by AutoZone and Advance Auto Parts. There's a small story here.
  • I went to test it at AutoZone yesterday and they couldn't run the test because they claimed that the battery was at 50% charge. This was when my IBS reported around 73% charge (per AlfaOBD via the Body Controller).
  • I put the Battery Jr. on it overnight after which the IBS reported 97% charge and AutoZone was able to run their "test" which didn't even involve increasing the engine speed. It tested GOOD
  • However, AutoZone kept seeing weird things around the battery. Once they were seeing "not enough reserve" when we entered 140 CCA for the expected reserve. ¯\(ツ)/¯.
  • The AAP Alternator test actually tested at 3000RPM and indicated GOOD.
  • The data captured with AlfaOBD indicates that the voltage requested while running is around 14.5 and we actually are seeing around 14.8VDC per the PCM.
  • Seeing 15->35% alternator duty cycle as reported by the PCM while running.
  • When the engine is not running, voltage reports being 12.5ish
  • My digital multimeter confirms these numbers
  • I also pulled out my TIPM/PDM, inspected and cleaned all connectors with electrical cleaning solution and re-installed it.

Now, the electrical gremlins appear to be gone. No more intermittent headlights or intermittent radios or HVACs or dashboards. Also, no more random automatic windshield wiper activations or seat moves. Also, no more check engine lights.

HOWEVER - I have the battery idiot light on the EVIC indicating, after engine start, that there is "Low Voltage" and the accompanying EVIC message. Before starting the engine, the CEL is lit and the PCM reports P063A. Immediately after starting the engine, the CEL goes away. I guess this is just indicating that the alternator was not working while the engine was not running, but the key was in the RUN position.

So I guess I'm going to keep an eye on the charge level of the battery and see if it gets worse and worse. I suspect that this is the case, but I'm totally flabbergasted at this point. What is responsible for telling the dashboard to enable the battery issue indicator and the EVIC to report low voltage? Where are we reading a low voltage, given that the PCM is seeing the correct values? And what can be done to further diagnose this? Finally, I'm willing to bet that this wont be the last time I see the intermittent, systemic electrical gremlins. If/when it happens again, I suppose that will give me a higher degree of confidence that there's a ground fault or some type of short that is rearing its head from time to time?

Perhaps @PatentlyPhil has some ideas? Or @Vice-White? Or @Buck99rog?

Thanks in advance,
-Randall
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Tin Foil Hat
If you are seeing the batt and CEL lights before you start the car or immediately afterwards for just a second or two, that is normal testing of the lights. It's entirely possible that your battery depleted too much of it's capacity when starting and that throws a low voltage message until the capacity is restored by the charging system. This would be an indicator of a weak battery. The only way to rule it out is with a new battery.
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Tin Foil Hat said:
If you are seeing the batt and CEL lights before you start the car or immediately afterwards for just a second or two, that is normal testing of the lights. It's entirely possible that your battery depleted too much of it's capacity when starting and that throws a low voltage message until the capacity is restored by the charging system. This would be an indicator of a weak battery. The only way to rule it out is with a new battery.
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I see the batt light after starting as well. Actually, the battery light and the message in the EVIC never stop after starting. They are not present before starting. The P063A is only present before starting I suspect because the alternator is not actually working in RUN mode when the engine is not running.

But it is a brand new battery. Die Hard Platinum, 850CCA, H7 AGM which has tested clean both at AutoZone and at Advance Auto Parts.
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Tin Foil Hat
Got it. I didn't remember you changing it. That should be good then. I can't help much now as I don't know how the various modules look at the battery voltage.
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Tin Foil Hat said:
Got it. I didn't remember you changing it. That should be good then. I can't help much now as I don't know how the various modules look at the battery voltage.
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Yeah man, that 9 year old battery was definitely due for a replacement :). Thanks again for smacking me with that fact on a prior thread. Sadly, the battery replacement alone did not solve all of the gremlins. Truth is, I do not know WHAT exactly stopped the gremlins. I think they just stopped about the same time that I got my OBDII Bluetooth adapter and cleared all of the old codes. Seems fishy.. Probably just the intermittent nature of this issue :(
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Tin Foil Hat
Some errors may not have come back because you have the new battery now. It takes time for the systems to get themselves back to normal. Except for the nagging battery light.
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Tin Foil Hat said:
Some errors may not have come back because you have the new battery now. It takes time for the systems to get themselves back to normal. Except for the nagging battery light.
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Sure, I can buy that it was a coincidence that my gremlins ended after the battery replacement AND some amount of "reset my brain" time :). Maybe the battery idiot light goes soon afterwards? :p
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r4nd4llm4n said:
Sure, I can buy that it was a coincidence that my gremlins ended after the battery replacement AND some amount of "reset my brain" time :). Maybe the battery idiot light goes soon afterwards? :p
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Also unfortunate is... My centrifugal supercharger air ducting (metal w/ rubber elbows) and the blow off valve are literally like right in the way of me getting access to the alternator to test the the batt+ or field loop from the ECU w/ the Pulse Width Modulation duty cycle managed by what I would guess to be a N-channel MOSFET controlled by the ECU via voltage on the gate to allow flow to ground via the drain (with source grounded).
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Buck99rog
After all you have tested and have had tested, the only things that I can think of are, wiring continuity tests from the TIPM to the EVIC or the TIPM is going out.

Depending how much salt air your vehicle has received over the years, it wouldn't be surprising to have some built up resistance in your wiring. Cleaning the contacts gave it some new life but, I would have to believe the TIPM, at this point, is "worn out".
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r4nd4llm4n said:
So I'm at. a total loss at this point, no idea where to go next...

  • I've cleared all of the old codes in all of the relevant modules
  • I've had the battery tested both by AutoZone and Advance Auto Parts - good - AAP's tester even stated that it could pull > 1000CCA from the 850CCA battery
  • I've had the alternator "tested" both by AutoZone and Advance Auto Parts. There's a small story here.
  • I went to test it at AutoZone yesterday and they couldn't run the test because they claimed that the battery was at 50% charge. This was when my IBS reported around 73% charge (per AlfaOBD via the Body Controller).
  • I put the Battery Jr. on it overnight after which the IBS reported 97% charge and AutoZone was able to run their "test" which didn't even involve increasing the engine speed. It tested GOOD
  • However, AutoZone kept seeing weird things around the battery. Once they were seeing "not enough reserve" when we entered 140 CCA for the expected reserve. ¯\(ツ)/¯.
  • The AAP Alternator test actually tested at 3000RPM and indicated GOOD.
  • The data captured with AlfaOBD indicates that the voltage requested while running is around 14.5 and we actually are seeing around 14.8VDC per the PCM.
  • Seeing 15->35% alternator duty cycle as reported by the PCM while running.
  • When the engine is not running, voltage reports being 12.5ish
  • My digital multimeter confirms these numbers
  • I also pulled out my TIPM/PDM, inspected and cleaned all connectors with electrical cleaning solution and re-installed it.

Now, the electrical gremlins appear to be gone. No more intermittent headlights or intermittent radios or HVACs or dashboards. Also, no more random automatic windshield wiper activations or seat moves. Also, no more check engine lights.

HOWEVER - I have the battery idiot light on the EVIC indicating, after engine start, that there is "Low Voltage" and the accompanying EVIC message. Before starting the engine, the CEL is lit and the PCM reports P063A. Immediately after starting the engine, the CEL goes away. I guess this is just indicating that the alternator was not working while the engine was not running, but the key was in the RUN position.

So I guess I'm going to keep an eye on the charge level of the battery and see if it gets worse and worse. I suspect that this is the case, but I'm totally flabbergasted at this point. What is responsible for telling the dashboard to enable the battery issue indicator and the EVIC to report low voltage? Where are we reading a low voltage, given that the PCM is seeing the correct values? And what can be done to further diagnose this? Finally, I'm willing to bet that this wont be the last time I see the intermittent, systemic electrical gremlins. If/when it happens again, I suppose that will give me a higher degree of confidence that there's a ground fault or some type of short that is rearing its head from time to time?

Perhaps @PatentlyPhil has some ideas? Or @Vice-White? Or @Buck99rog?

Thanks in advance,
-Randall
Click to expand...
The target charging voltage can be different than system voltage. It SHOULD be within 0.2V - how were you viewing that data? Using the graphs/live data or just doing a report from the PCM? Check using live data. A few thing I'd do next:

  • I'd double check the alternator test - with the engine running you should back-probe the red wire on the alternator. It should read about 3.5V lower than the voltage at the output stud. Confirm that's the case. If it is, then the sense circuit is working OK. If it's not, then that circuit is failed/failing. It's not serviceable, so the alternator would need to be replaced.
  • Check voltage drop between the battery + post under the hood, and the alternator stud. Also check against the PCM's B+ terminal. Both should be under 0.2V.
  • Check voltage drop from battery - to the engine and body grounds. Also should be less than 0.2V.
If everything checks out, and you've triple checked all of the grounds on the body/engine to make sure they are clean, tight, and without any corrosion, then it's very likely the problem is the PCM itself.

One note that the pins on the PCM are VERY sensitive - to the point that MOPAR tells you not to touch them or damage WILL occur (you have to use a $2k breakout board to test PCM I/O's, according to the manual). I'm not sure that's actually true or not, but a loose connection at the PCM could be the cause of all problems.

All this said - my bet is that the BCM is fine and the error is either a ground issue or alternator issue. I am, of course, assuming that you've checked and re-checked all fuses.
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PatentlyPhil said:
tage can be different than system voltage. It SHOULD be within 0.2V - how were you viewing that data? Using the graphs/live data or just doing a report from the PCM? Check using live data. A few thing I'd do next:
Click to expand...
It was definitely live data in the plotting section, tab 7 if I remember right.

PatentlyPhil said:
I'd double check the alternator test - with the engine running you should back-probe the red wire on the alternator. It should read about 3.5V lower than the voltage at the output stud. Confirm that's the case. If it is, then the sense circuit is working OK. If it's not, then that circuit is failed/failing. It's not serviceable, so the alternator would need to be replaced.
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Grumble grumble, the blower plumbing is in the way :/. Ill see if I can get at it from behind... on a stool :). Couldnt getot the bat + there either while running.

PatentlyPhil said:
  • Check voltage drop from battery - to the engine and body grounds. Also should be less than 0.2V.
If everything checks out, and you've triple checked all of the grounds on the body/engine to make sure they are clean, tight, and without any corrosion, then it's very likely the problem is the PCM itself.
Click to expand...
So my FSM is for the older 2012 durango. It was entitled Dodge Durango 2012 -> 2016, but I imagine there are some obvious differences. I also do not have the factory electrical schematics/diagrams. I guess I can get those from that service that seems to be sources from a library in Tennessee? I will need to figure out where all of the serious grounding points are to do a thorough test. I know that there's the one on the firewall and a couple under the center console, but the rest I have no idea yet.

PatentlyPhil said:
All this said - my bet is that the BCM is fine and the error is either a ground issue or alternator issue. I am, of course, assuming that you've checked and re-checked all fuses.
Click to expand...
Ok so I check, but not RE-check all fuses :). Ill add that to the list.

Thanks again for all yall's help on this. Specifically and most recently @PatentlyPhil, @Buck99rog , and @Tin Foil Hat . Obviously, the dealer is not super useful for me here as they have understandably stated I've taken the truck too far from stock for them to want to bother. HHP is clear down in Smyrna, DE which has to be 1.5 hrs if not more from here. And my close friend who is a former dodge tech and current shop owner is at least 50 minutes away in Northern Delaware :(. I think I'm gonna get this problem squared away! I wonder if there was a ground strap missed or not fully secured when the 6.4 was swapped. It's not impossible. I had my vac line between the throttle body and the EVAP which was also split into for my blow off valve and AEM boost/afr gauge/failsafe clogged up for a while before I noticed why the heck I was getting turbo flutter on my supercharger and was not getting any boost gauge reading. Why not other things. A motor swap is not the least invasive thing to do to a truck.

Best regards,
--Randall
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PatentlyPhil said:
I'd double check the alternator test - with the engine running you should back-probe the red wire on the alternator. It should read about 3.5V lower than the voltage at the output stud. Confirm that's the case. If it is, then the sense circuit is working OK. If it's not, then that circuit is failed/failing. It's not serviceable, so the alternator would need to be replaced.

Check voltage drop between the battery + post under the hood, and the alternator stud. Also check against the PCM's B+ terminal. Both should be under 0.2V.
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So @PatentlyPhil basically, Im unable to reach or even see/feel the battery+ stud on the alternator. the case is ground and there's no voltage drop between the jumper stud ground and the alternator case. but literally the entire wiring harness on that side leading from passenger side of the hood (so PDC + PCM + other) is pinned up there behind the alternator and the supercharger plumbing is blocking the way from the front/top. I will have to see if there's any way to reach it from the bottom. I guess I could also move the things out of the was as long as I only intend to idle since there's no real boost at idle.

When you say the b+ on the PCM, you're not referring to b+ on the PDU right? I'll have to poke around and find b+ on the PCM if there's another.
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r4nd4llm4n said:
So @PatentlyPhil basically, Im unable to reach or even see/feel the battery+ stud on the alternator. the case is ground and there's no voltage drop between the jumper stud ground and the alternator case. but literally the entire wiring harness on that side leading from passenger side of the hood (so PDC + PCM + other) is pinned up there behind the alternator and the supercharger plumbing is blocking the way from the front/top. I will have to see if there's any way to reach it from the bottom. I guess I could also move the things out of the was as long as I only intend to idle since there's no real boost at idle.

When you say the b+ on the PCM, you're not referring to b+ on the PDU right? I'll have to poke around and find b+ on the PCM if there's another.
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So Im all out of ideas now. For a week or two there were no gremlin events, only the EVIC, the battery light, and the low voltage message. That ended Friday night. The gremlins were in full effect. "Shift into park, stop engine, start engine" with a limping transmission that felt like it was slipping quite a bit. Headlights literally blinking, Windshield wipers fully crazy randomly on and off, and the dashboard and center stack turning on and off again. Oddly enough, during these events, the low battery voltage message and corresponding indicator were NOT lit. It threw a load of check engine lights. This time it was more clear and concise. The system overall is complaining of too much voltage. Its reading 14.8 per the PCM and a digital multimeter and 15.low on the EVIC and only 14.5 is being "requested" by the PCM per statistics I pull from the PCM/Engine with AlfaOBD while its running. Is this really enough of a disparity to be causing all of this nonsense? What's half a volt among friends? There are no more latent low voltage PCM codes. Im also not seeing the "lost communication with <module name>" coming out of the various modules either. The modules most tripping out in these events are the PCM, the BCM, the TCM, and the TCCM as well as the ABS controller.

I've still been unable to get clear access to the back side of the alternator to test the batt + and the PWM duty cycle field circuit... Its really in a hell of a spot. Can't really get to it from below either :(. I think Im going to need to pull some intake tubing from the intercooler and the blow off valve to get to it. Ill have to crank it with the S/C disconnected from the intake which shouldn't be too huge a problem for stationary testing (not a dyno pull, but).

I've also not found any loose ground straps yet. I've not FOUND all of them, mind you... I did go back and check most if not all of the fuses in the PDC and that was after cleaning the contacts in the connectors and the plugs leading into it with electric parts cleaner and a couple of different material brushes.

I just have to say, this problem is a giant pain in the buttocks. Im willing to bet a professional mechanic (i.e. a dealer or non-high-performance shop) would have just started replacing things one at a time like the Alternator then PCM and so on. I may yet resort to something similar, but I'm still hoping to catch the smoking gun. Thanks again to those who have helped heretofore!
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Man, this is getting exciting... as a bystander...

The 0.3V difference is close enough for government work. Was the BCM also reporting 14.8? It would be odd if there were a mismatch between BCM and PCM readings for voltage. The EVIC is where I'm stuck. That shouldn't read differently. I don't know if the EVIC gets voltage from the CAN or from the harness. You could check voltage at pin-10 or pin-20 on the back of the EVIC connector. If I had to wager a guess, I'd say it gets voltage from the CAN because that data is already there.

On the other hand... It's entirely possible we are overthinking all of this and it could be something silly like a failed Intelligent Battery Sensor. The IBS spits data directly into the BCM via the LIN bus, and the BCM spits it out from there on the CAN bus.

Easiest thing to do would probably be just unplug the IBS and then see what the BCM does.

For comparison, here's what my '14 shows in System ID for the BCM:

Battery:
IBS Activate MWU: No
Battery Type: Battery ID 6
IBS Quiescence Current Limit (-250-0 mA): -250.000 mA
IBS Minimum Voltage Limit (0-25.4 V): 5.000 V
IBS Minimal Charge Limit (0-125 Ah): 10.000 Ah
IBS Standby Time (0-7620): 7620.000 sec
IBS Minimum Charge Limit (0-2500mA): 600.000 mA
LIN and Misc:
IBS Present: Yes

And has the following Status:

Intelligent Battery Sensor(IBS) Data 1:
Intelligent Battery Sensor Measured Voltage: 14.58 V
Intelligent Battery Sensor Current Range Sensor Setting: 200
Intelligent Battery Sensor Current: 7.40 A
Intelligent Battery Sensor Temperature: 17 Deg.C
Intelligent Battery Sensor Quiescent Current: 0.69 A
Intelligent Battery Sensor Current Error: No error
Intelligent Battery Sensor Temperature Error: No error
Inteligent Battery Sensor Error in Calibration Data: No
Intelligent Battery Sensor Error in ECU Identification: No
Intelligent Battery Sensor Error in NVM Data: No
Intelligent Battery Sensor Response Error: No

Edit: What were the codes thrown?
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Is the CAN actually 12VDC? I've never checked it per se. I know that most TTL likes 5VDC and most Digital likes 3.3VDC. But PC/Server PSUs all output 12VDC, 5VDC, 3.3VDC, and I think a negative rail too at least for -12VDC and -5VDC though these are legacy and no longer necessary. But feeding 12VDC into a computer seems odd. I guess all of the car control modules could all have little buck converters in them or even linear regulators. But 12VDC as the peak voltage for the CAN bus? That kind of voltage would fry any GPIO inputs on a modern computer processor :). I believe the terminators on CAN are 60 ohm? With ohm's law, that's about 200ma of current at 12VDC... 2.4 watts. That's not a LOT, but it's a lot more than I'd have guessed :)

Ill get that new set of codes and logs moved over from the laptop in a bit :/
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CAN, as used in any ISO 11898 compliant system, is only ever 5V with 120 ohm terminators (for the high-speed bus. The low speed bus uses a resistor at every node).

The modules themselves all operate at 12VDC with a step-down though just about every sensor operates at 5V as you'd expect.
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PatentlyPhil said:
CAN, as used in any ISO 11898 compliant system, is only ever 5V with 120 ohm terminators (for the high-speed bus. The low speed bus uses a resistor at every node).

The modules themselves all operate at 12VDC with a step-down though just about every sensor operates at 5V as you'd expect.
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Interesting that the modules take in 12VDC and bring it down to 5VDC, independently at each controller. But then again, I guess its atypical to have anything other than 12VDC being delivered directly by wiring in a combustion engine vehicle. Furthermore, some of the wire runs would probably see a bit more loss at 5VDC than at 12VDC. That said, having a voltage regulator at each device makes me wonder why 0.3VDC over would make a damned bit of difference. Most voltage regulators I know generally operate with a fixed output voltage given a rather large comparatively speaking in the range of output voltage to output voltage * 2 or 3 give or take either due to feedback for a linear regulator or due to the frequency of the oscillator and the action of schottky diodes for a buck converter.
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PatentlyPhil said:
CAN, as used in any ISO 11898 compliant system, is only ever 5V with 120 ohm terminators (for the high-speed bus. The low speed bus uses a resistor at every node).
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These numbers work better :). 120ohms at 5volts is 42 milliamps :p. 208 milliwatts.
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So I have some new info! Maybe helpful, maybe not. Today, it was freaking out enough that I noticed a couple of things.

1) My backlighting/LED display on my AEM AFR/Boost Gauge/Failsafe was dark/off during the "electrical seizure" event. This device pulls power straight from the PDU under the hood using a terminal designed to slide into the fuse block for a given circuit. This isconnected through F93, which I believe is the circuit that leads to the fuel door release mechanism. I guess it's a pulsed electromagnet that opens a latch, and the spring on the fuel door does the rest. Either way, This connection is straight from the PDU, which, in turn, is straight from 6-ish gauge wire that connects to the battery bus under the hood. For this to be dark, does the issue have to be either bad ground or a bad PDU? The next step is to remember where I ran the black wire from this gauge :). I'm also going to see what the schematics say about that circuit labeled F93 in the PDU/TIPM. I may slap a voltmeter inline with that 12V + connection to the failsafe gauge, but with its connection to the battery negative terminal. That would tell me right on if it's a ground issue as the gauge would NOT be working, but the voltmeter would still be powered and seeing a potential vs. ground/

2) The shifter light indicating P R D N on the dial gear shifter would go dark too at the exact moment that the EVIC started complaining about the transmission and telling me I had to shift into the park and stop the car. I know I've had the center console open and have seen and had in my hand the harness responsible for this connection. I've also double-checked 100% that the two primary ground straps coming from the same harness and connecting to the body/ground plane on metal underneath the console are secured tightly, well-grounded, and not in any way oxidized or crusted over with spilled coffee or whatever :). Furthermore, I was rolling about two mph when it happened with the trans, and it sounded like it went into park and klunk-rolled to a stop. I was pretty startled as were the teachers waiting on the sidewalk as I picked up the 4th grader :)

3). The passenger had their window down, but while the truck was having its seizure, the window would be automatically raised. How.... I can't even describe how this might be a thing. It was creepy for sure... and of course the radio/hvac restarts and the wiper motors really make for a ride that a passenger can really be at ease for... or not :)


So, useful info or not so much?
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