[7.3 lifer]

I have been fighting with a GP problem for months. Normally dont need them, but cold weather is different. The WTS light comes on, and if I wait, I get DTCs for glow plugs malfunction. But usually I just hit the start and done. I have tracked down the problem to no ground circuit completion from the ECU. This is a Calif truck so it has the electronic control module for the GP and a solenoid for the intake heater. Both are receiving power, glow plugs are a few months old(Motorcraft) and all show proper continuity, but they will not energize and there is no continuity at the ground circuit from ECU. Does the OTS only monitor temp for this purpose or for other engine management functions too?
Any suggestions appreciated.

 

[7.3 lifer]

Just to clarify my above post...... this is in my '00 7.3L Calif cat exempt truck.

 

[klhansen]

If the PCM isn't sending a ground signal to the GPCM, then you'd either have to replace the PCM or wire in a separate circuit with a switch to manually ground the GP activation circuit. But I'd post the codes you got here and we can check to be sure the problem isn't the GPCM.

 

[7.3 lifer]

KlH, thanks for the response. I failed to mention that the GP module was replaced with the GPs, per suggestion of previous owner, who had the prob diagnosed just before selling the truck. I have power to both the GP module and the intake heater relay. Just no continuity in the ground circuit to both. The codes are for all 8 GPs but nothing else.
Everything worked for a short time after replacement, but then GPs quit and wont come back to operation. When I ran some checks, with cold engine, I found the ground circuit problem. Is it possible that if the oil temp sensor/circuit is bad that it's not communicating with the PCM? No codes indicate that, but curious.

 

[klhansen]

The EOT circuit wouldn't affect the GP controller. If it's unplugged or broken, the PCM uses default information (assumes starting and running temps), so that shouldn't be your problem.


If the GPCM isn't getting power (ground circuit broken?) then it wouldn't power up or turn on the GP's. I'm not sure how that would affect GP codes, but I'm guessing it wouldn't get any codes at all because they initiate in the GPCM.


Here's a wiring diagram for the GPCM. There are actually two wires between the GPCM and the PCM, and it's probably grounded thru the mounting bolts. You should check continuity on all the wires.