2002 PCM issues - Multiple failures - interesting case - need help to solve

[Electro7]

It’s a 2002 Ram 1500 with 4.7L, 166k miles. Truck runs great.

One day, the running (parking) lights stopped working.

Traced problem to an "open" in the PDC (Power Distribution Center/Fuse Block). In this year truck, the PDC is plugs and connections only, no electronics). Unfortunately, during the troubleshooting process, I got the following failures (the failures suddenly appeared during troubleshooting):

1. Speedometer does not work
2. ABS waring Light
3. Brake warning light
4. Airbag waring light
5. A/C clutch does not engage

I replaced PDC (fuse block) with exact part number and revision (verified pins are identical).

Running lights and all else works fine. Still have above failures with a P0500 (VSS Error) code. Disconnected battery (hard reset), drove vehicle. Code does not come back. Still have same 5 errors.

I replaced the FCM Front Control Module with the exact part number and revision - no change. I put the original FCM back in. Tested all relays and fuses. No change.

Note: The above failures are present with both the old and the new PDC. The only difference with the new PDC, is the running lights now work.

From what I gather by poking through the book is:

• If the PCM isn't reading the VSS, the speedometer, ABS, and A/C will not function.
• If the ABS module isn’t communicating with the PCM, you will get ABS and brake warning lights.
• If the PCM needs programming, the truck may not recognize critical signals (speed, A/C, airbag module)

My questions

• Did I short something out during my power-on troubleshooting? Did I cook the PCM?
• Could it be a bad wire / loss of VSS signal / coincidentally a bad VSS module
• Could it be just the PCM reprogramming needed? If so, how do I do it - dealer?
  
  Suggestions will be greatly appreciated. Thanks
  
  Thanks
  

 

[Daw14]

Sounds like your battery is going dead , lots of dash lights suddenly is a sign.

Have your battery LOAD TESTED with a toaster style tester. This puts a load on the battery which mimics the starter .

 

[Electro7]

Battery is new and has been tested - thanks

 

[16 Bighorn 4x4]

This is posted in the wrong forum. A 2002 1500 is a 3rd gen pickup.

 

[fredd4]

I have the same 1500 RAM 4.7L 2002 and just had the same issues, no speedo, no odometer, ABS and break warning lights on. Most complaints with this issue have tried replacing the vss without any improvement. Some YouTube videos suggest the most likely cause is the power distribution connectors under the fuse box not supplying the proper voltage (or no voltage) to some of the fuses. In particular fuse #35. I'll check this tomorrow and post my results.

 

[HemiLonestar]

In both cases, a 2002 1500 is a 3rd gen, not a 2nd gen. Try there.

 

[fredd4]

Replaced the sensor on the differential, but wasn't the problem. I'm still looking for a solution. The closet self test cycles the speedo so Im assuming the speedo is probably ok. Also, if an admiistrator reads this can it be moved to the ten 3 forum?

 

[fredd4]

To Electro7, Did you find any solution to your issues? There's a YouTube post that seemed to suggest the problem may be corrosion of wires/connectors under the fuse box not supplying the right voltage to some circuits.

 

[fredd4]

To Electro7, after replacing the sensor on the differential without any help I'm still trying to trace the problem: P0500, no speedo or odometer, the ABS and breaklight light on the cluster display, although the AC works. Tested good voltage on the fuses so the connectors underneath are probably ? ok. Any luck tracing the problem? If it's a broken or shorted wire it'll be hard to track down

 

[RamDiver]

To Electro7, after replacing the sensor on the differential without any help I'm still trying to trace the problem: P0500, no speedo or odometer, the ABS and breaklight light on the cluster display, although the AC works. Tested good voltage on the fuses so the connectors underneath are probably ? ok. Any luck tracing the problem? If it's a broken or shorted wire it'll be hard to track down

It appears that Electro7 has bailed. If you roll a mouse over or click on the username, this window will appear.




I was reviewing a 2001 service manual, and it states that the rear wheel speed sensor signal is fed to the Controller Antilock Brake module (CAB) and from there to the ECM.

The service manual indicates to first disconnect the negative battery terminal and then release the connectors on the module for inspection.

Do you have access to a digital multimeter? If you could measure the resistance of the wheel speed sensor at the axle and then at connector C1 on the CAB, across pins 1 & 8.

This might confirm that the correct signal is arriving at the CAB module.
Or, the wiring path isn't compromised.

See the attachment for pinout info.

.

 

[fredd4]

RamDriver, thanks for the heads up. I'll check the CAB connector 1-8 pins if I can locate the CAB. The location sketch I downloaded shows it just below the brake fluid reservoir but I don't see it there.

 

[RamDiver]

RamDriver, thanks for the heads up. I'll check the CAB connector 1-8 pins if I can locate the CAB. The location sketch I downloaded shows it just below the brake fluid reservoir but I don't see it there.

You're most welcome.
See if this attachment helps to point you in the right direction. I'll look around for a better picture.

I finally found a link for the 2001 Service manual.

https://www.ramforum.com/threads/pdf-service-manual.32145/post-2838578

.

 

[fredd4]

Michael, just getting back to work on this issue -thanks for the pdf. I think I found the CAB module behind and below the battery, so I'll br trying to remove the two connectors today.

 

[RamDiver]

Michael, just getting back to work on this issue -thanks for the pdf. I think I found the CAB module behind and below the battery, so I'll br trying to remove the two connectors today.

The manual instructions indicate the battery's negative connection should be removed first.
Once you have the connectors off, inspect the connections for damage or corrosion and then verify the wiring path from the sensor to the CAB module.

.