no glow plug relay signal

Rubyred · Aug 7, 2016

hi all. earlier this summer I had some cold start issues, the glow plug relay would not always activate glow plugs. well once the weather got warmer it would start up no problem, but CEL would come on soon after i started it (P0670 Glow Plug Control Circuit Malfunction and P0683 Glow plug diagnostic signal communication fault. things i have done:

Replace glow plug relay with a new Motorcraft unit, No Change
Check key power on Red wire of relay....source voltage. Good
Ohm tested PU/OR wire from PCM connector to relay, .02ohm Good
Also load tested PU/OR wire with power probe, Good
Tried another PCM from my good running 00 7.3. No Change
Unplugged F5 chip. No Change
Tried different MAP sensor and Oil temp sensor off my other truck. No Change
With key on, if i use a jumper wire to ground out signal side of relay it kicks on and i have 11v on the output side fro my glow plugs.

Something is keeping the PCM from grounding the signal side of that relay and i am at my wits end of what it could be. I read that the PCM watches Engine Oil temp and the BAROmeter to determine IF and how long to activate glow plugs that's why i tried different sensors from my known good running truck. the only other thing i have yet to try is run my own wire from PCM to signal side of relay to make ABOLUTELY sure there is nothing shorted or inhibiting the signal side of the circuit from doing its job, which is what my codes are for.
any help or speculation is appreciated, im about to pull my hair out.

Truck is a 2001 F250 4dr long box. 6spd all stock with F5 chip and infinity display XPC4 pcm code

Justin@DP-Tuner · Aug 11, 2016

Rubyred said:
hi all. earlier this summer I had some cold start issues, the glow plug relay would not always activate glow plugs. well once the weather got warmer it would start up no problem, but CEL would come on soon after i started it (P0670 Glow Plug Control Circuit Malfunction and P0683 Glow plug diagnostic signal communication fault. things i have done:

Replace glow plug relay with a new Motorcraft unit, No Change
Check key power on Red wire of relay....source voltage. Good
Ohm tested PU/OR wire from PCM connector to relay, .02ohm Good
Also load tested PU/OR wire with power probe, Good
Tried another PCM from my good running 00 7.3. No Change
Unplugged F5 chip. No Change
Tried different MAP sensor and Oil temp sensor off my other truck. No Change
With key on, if i use a jumper wire to ground out signal side of relay it kicks on and i have 11v on the output side fro my glow plugs.

Something is keeping the PCM from grounding the signal side of that relay and i am at my wits end of what it could be. I read that the PCM watches Engine Oil temp and the BAROmeter to determine IF and how long to activate glow plugs that's why i tried different sensors from my known good running truck. the only other thing i have yet to try is run my own wire from PCM to signal side of relay to make ABOLUTELY sure there is nothing shorted or inhibiting the signal side of the circuit from doing its job, which is what my codes are for.
any help or speculation is appreciated, im about to pull my hair out.

Truck is a 2001 F250 4dr long box. 6spd all stock with F5 chip and infinity display XPC4 pcm code

An XPC PCM is a DPC-421, which does not have any glow plug monitoring capabilities.

Those codes should only throw if you are using a California model PCM. This would be either a DPC-431 or DPC-451 (for manual trucks).

Disconnect your chip, then go into Vehicle Info under the Tuning menu on your Infinity. What is the Strategy?

Rubyred · Aug 16, 2016

After a while with no replies on this thread i made an appointment with my local dealership to look at it. Like i said i read quite a bit on this simple glow plug operation and i couldnt get it to function as designed. As embarrassed as i am i took it to a dealer. I will try unplugging the F5 chip and looking up the strategy like you suggested. What strategy am i hoping for?
Thank you for the reply

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Justin@DP-Tuner · Aug 16, 2016

Rubyred said:
After a while with no replies on this thread i made an appointment with my local dealership to look at it. Like i said i read quite a bit on this simple glow plug operation and i couldnt get it to function as designed. As embarrassed as i am i took it to a dealer. I will try unplugging the F5 chip and looking up the strategy like you suggested. What strategy am i hoping for?
Thank you for the reply

Sent from my iPhone using Tapatalk

Well if the PCM is in fact an XPC4, your strategy will be VOAA8Q4.

Rubyred · Aug 16, 2016

This is the current strategy, but i have my pcm from my 00 auto truck PCM code NVK5 the truck throws the same code and does not activate glow plug relay no matter which pcm is in it

Justin@DP-Tuner · Aug 17, 2016

Rubyred said:
This is the current strategy, but i have my pcm from my 00 auto truck PCM code NVK5 the truck throws the same code and does not activate glow plug relay no matter which pcm is in it

That strategy shows a MNM1 PCM code. This is a DPC-422 PCM. Meaning for a Federal Auto truck. Are you reading the strategy with the chip on the PCM?

Justin@DP-Tuner · Aug 17, 2016

Also, you are sure you have a GP relay and not a GP control module?

https://www.dp-tuner.com/kbase/Locating_your_PCM_Code/How_Do_I_Find_My_PCM_Code_.html

Rubyred · Aug 17, 2016

Yes im sure i only have an intake relay and glow plug relay, same with my 00 auto truck i swapped PCM's with. I put the XPC4 in my auto truck and it fires up pefect and has no check engine light

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Justin@DP-Tuner · Aug 18, 2016

Rubyred said:
Yes im sure i only have an intake relay and glow plug relay, same with my 00 auto truck i swapped PCM's with. I put the XPC4 in my auto truck and it fires up pefect and has no check engine light

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Okay. Very strange. Those codes should only throw on Cali emission trucks. Did you purchase the chip directly from us?