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2012 Ram Promaster 1500 no powertrain bus communication

Shane Technician Massachusetts Posted Latest

Question

Resolved

Network Communications

2014 Ram ProMaster 1500 3.6L (G ERB) 6-spd (62TE) — 3C6TRVBG4EE104619

U1000-87

U1701-87

U1706-87

U1722-87

U1712-87

No Crank / No Start

No Communication

Hello everyone, I've got a vehicle that's making me scratch my head. 2014 Ram Promaster 1500 gets towed in no crank, no start. I verify the concern and it in fact wont start, I connect a scan tool and do a code scan. I also noticed on the scanner that battery voltage was low, about 10.8V key on, so i charged the battery. Obviously still a no start. Noticed no PCM in code scan and lots of communication codes. looked at the network diagrams on alldata and everything on CAN C is not talking except BCM. Took key out and wait for it to go to sleep, has 60 ohms at BCM connector C8, and anywhere in the system i check. I pull out the scope and checked the network. Blue and Red are CAN high and low back probed at BCM and Green and Yellow are at DLC. This network looks good to me but noticed when i unplug BCM everything is gone, seems like BCM is only thing talking, also noticed looks like it keeps repeating the same message continuously. unplugged PCM and can still see BCM talking. I checked at PCM and can see the BCM messages. Identifix has ESM as most common problem so i unplugged and bypass with same result, network doesn't appear to be down so I didn't think this was going to do anything. Seems to me the network is good but why are no modules communicating.

I checked and load tested all powers and grounds at PCM and everything is there. I read discription and operation and says ignition switch sends power over 2 circuits to BCM ( confirmed this checking BCM pids and checking for voltage on wires and all good) then BCM sends wake up message to appropriate modules. So is the BCM not sending the wake up signal or are 4 different modules not seeing the wake up message? seems to me the BCM is the culprit, I have 1 ordered and will be here on Friday. I do have Wii tech and IM608 so I should be all set there. Does anyone know of anything else i need to check before replacing the BCM? For some reason I don't feel confident a BCM is going to fix this car.

network diagrams i scribbled out the modules this vehicle doesn't have, checked mark are communicating and outlined are not communicating.

included screen shot and scope file

Blue is CAN low at BCM connector C8 pin 14

Red is CAN high at BCM connector C8 pin 13

Green is CAN high at DLC

Yellow is CAN low at DLC

anything i missed testing or adding to this post please let me know

Michael Technician

New Hampshire

Michael

I had a van a week or so ago, and ultimately found the airbag module was shorted to ground, on 1 of the can bus lines. I tested basically as you did, just added the short to ground test.

Ð Awarded

Shane Technician

Massachusetts

Shane

This can bus doesn't look shorted to me you can see the messages look good.

Ð Awarded

Caleb Diagnostician

Indiana

Caleb

This is just my opinion. The waveforms look fine. However I don't like how the 2.5 volt bias goes ways down before the next message. In my limited experience this is usually due to a lack of B+ or IGN power to multiple modules. Me personally I would pick a module who is offline (PCM for example). Check all B+, IGN, Wake up signals, etc to it. See if your missing anything.

Ð Awarded

Agree

Shane Technician

Massachusetts

Shane

I only checked the pcm. But it has all powers and grounds the wake up is a message over can network

Ð Awarded

Stephen Technician

Tennessee

Stephen

I think the lack of continuous 2.5V bias is the key to this problem.

Ð Awarded

Michael Diagnostician

New Jersey

Michael

They run a ~10awg +12v feed from the battery, under the floor mat and up the A piller. I've had a bunch of them break under there and cause strange issues.

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Helpful

Dmitriy Analyst

Ontario

Dmitriy

Shane, you’ve done all the right testing, but the BCM has some weird codes, and the Instrument cluster does not like messages from the BCM. So, it would be interesting to see how the new BCM with proper software behaves — the easiest way is to wait until Friday then?

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Helpful

Shane Technician

Massachusetts

Shane Update

So the BCM came early and I installed it. Had to use Wii tech to write Vin to BCM , I don't have an LSID so IM608 pulled the pin. Input that into Wii tech then config restore and proximity alignment, uset IM608 to relearn keys. Now I have CAN C bus back but still no PCM. Reconfirmed powers, grounds and network, then ordered a PCM and currently waiting for that to come in.

Update Ð Awarded

Shane Technician

Massachusetts

Shane Resolution

So a brand new PCM arrived today and installed it and now have communication with PCM. Programmed learned Vin and mileage and learned keys vehicle, now it is a crank no start. Had an RPM on scan tool and if I added propane it would run, it was difficult to get to the fuel pressure line under the intake so I popped the fuse box cover off and noticed one relay was different than all the rest. It…

Resolution Ð Awarded