Fixing PCM communication error - no-crank & radio giving anti-theft code error

ramlover1991

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Hi all,

I am just posting this here as I have encountered this last week and finally found a resolution to this problem in my 2013 Ram 1500 with the 3.6L V6 engine (SLT).

Last week, I came to get into my truck and I turned the key, and... * nothing *
Keys were definitely being detected and I did have all the lights light up like a Christmas tree in the dash, and the radio gave an anti-theft error code.
Scanned the truck with an affordable Amazon OBD2 code reader/clearer and had error U0100.

Symptoms are as follow:
-Truck does not crank or turn over when turning the key.
-Dash has power and everything lights up, says to service airbags, 4WD, traction, etc.
-Red anti-theft/immobilizer red dot flashes with key in run position.
-Radio gives anti-theft incorrect code error, and doesn't function normally.
-Error code U0100 with a OBD2 scanner.

Troubleshooting began with the obvious:
-Check power, I wasn't using the truck as often due to us having another smaller VW (to save on gas when grocery shopping - going to the office, etc.), so I thought low-ish battery might be a culprit. Battery was a bit low (12.7V) and so I removed it from the truck and charged it overnight. Result: no change, still the same symptoms.
-Replaced keyfob batteries (in both fobs) with new CR2032 batteries. Result: no change, still the same symptoms.
-After reading online quite a bit trying to find this exact issues, I thought maybe the ignition module was going bad or had some dust bunnies interfering with the signal. removed the bottom part of the dash and removed the ignition module with 4 torx 20s, and removed the back cover and cleaned out the actual electronics of the module with some light dusting of compressed air. Result: no change, still the same symptoms.
-Started thinking this might be a PCM problem - looked up some diagnostics online (https://www.justanswer.com/car/ffqm5-2017-ram-1500-3-6l-no-communication-pcm.html): process is to check fuses 64, 63, 78, 22. All fuses were good.
-Next step in the diagnostics protocol is to check for pin/wire 96 of the driver-side connector to the PCM (PCM has two "strands" coming from the harness connecting to it), and is a RED wire (solid red, no stripes). To get easy access to the wires, take a flat screwdriver and gingerly pry the 90-degree cover off, it should come off fairly easily and expose the harness wires. The pin/red wire at position 96 should get battery voltage with the key in run position. I probed it with (I had to back-probe it with a very sharp multimeter prong through the sheathing). I get between 0.156 and 0.170 volts. Huh, interesting, we may have a culprit.
-Using the diagrams (attached to this post), I traced back the red wire to be connected to Fuse 22 in the fuse box. Tested to see if I had continuity with my multimeter between the probing point on the red wire (wire 96) at the PCM, and the fuse pin (with the fuse removed). No continuity.
-I am now thinking.... how the hell do I get a *single* broken power wire smack in the middle of the harness??? Anyways.... remove the air box, plastic intake, and disconnect the sensors and line to get better access to the harness right over the engine.
-I verify that I have continuity between the fuse pin in the fuse box and the wire underneath the fuse box (going into the harness) at fuse 22. Good continuity. So it seems the problem/break is between the wire from the fuse box and the PCM!!
-I run a temp wire with alligator clamps from the battery positive to my sharp multimeter probe end, and backprobe the PCR to make the connection. With a friend, we hold our contraption in place and turn the key. Radio music comes on and the truck turns over and starts! We have now figured out the problem - the 12V battery power cable in the harness going to the PCM somehow has a break in it, preventing the truck from starting!
-I open up the harness a bit at the middle of the engine bay and by using side cutters, gently nibble at the harness tape slowly to eventually free enough wire so that I can extirpate the red wire from it, and probe it as well. I have continuity from the fuse box to the middle of the engine. However, from the middle of the engine to the PCM, no continuity. My break is therefore on the passenger side of the harness. I however have no plans on replacing the wire.
-We cut the #96 solid red wire wire 4in below the fuse box, and about 4-5 in from the PCM connector (effectively cutting the wire on both ends - not in my plans to open up the whole harness to delete or repair a single wire...).
-We then run a copious lenght of 16AWG red wire from under the fuse box and all along the engine bay (by the top edge, tiewrapping it where we can to secure it, and tucking it in behind the heat shielding of the firewall where we can) and split it to the cut red wire from the PCM connector.
-Cleaned it all up, got some wiring harness tape from Amazon to reclose everything we opened up, and we put electrical tape over the wires we poked throughout the process.
-Truck runs great and with this solved, and clearing the codes,it's good as new! Happy to have solved this issue without a trip to the dealer, and for less than <50$ (not counting the time and dinner/breakfast I got for my good buddy and my girlfriend helping me troubleshoot this)

Sorry for the wall of text, just wanted to document this finding, in hopes it will help someone else!




 

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Daw14

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Thanks very much for sharing this information with us , I am certain others will benefit from it .
 

Jeepwalker

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...Thanks very much for sharing this information with us , I am certain others will benefit from it .

Totally agree. Thanks for sharing. Just goes to show just about 'anything' can happen.

Fantastic job sleuthing out the wiring problem BTW! That kind of issue could have caused lesser mechanics/techs/owners/troublshooters to replace umpteen parts ...can you imagine???! I'm going to log this issue in the back of me ole noggin'!!
 

BadHemi2014

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Wow! What a great write up.

I guarantee people will benefit from this. You really laid out your troubleshooting steps. That will help even with a different problem.
I still have a washer pump and dome light that don't work. Hmm time to get busy.
 

markeddawson

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I have these exact same symptoms on a 2014 Ram 2500 diesel. Checking the fuses and wiring this week. Hopefully it's a wire and not the TIPM or ECM.
 

Jeepwalker

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I've watched enough TV to know it's usually the red wire (not the blue one)...

:waytogo:
 

RamInfo

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Great write up, thank you for posting it!
 
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