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I have a 2003 7.3 powerstroke. Glow plug relay does not work, I've replaced it 3 times with no luck. Key off: power from batteries, no voltage on pcm ground, 12v control power, or glow plug feed circuit. Key on: power from batteries, voltage on pcm ground, and 12v control power, no power to feed circuit. Figured it was a bad relay, replaced 3 times and same issue every time, with key on if I connect the battery to the power feed circuit it will activate glow plugs. Any help is appreciated.
Disconnect the PCM ground wire from the relay, and ground the relay coil manually - does the relay close, and provide battery power to the glow plugs? If so, you're down to a possible open wire between the relay and PCM, or a defective PCM GPR control circuit, I think.
You could disconnect the batteries, disconnect the PCM connector, and check for continuity, open, short of the PCM control wire between GPR and PCM connector next. Pin 101 on the diagram below:
Do you have a compatible code reader? Would be good to see what the PCM is reporting, if anything.
There was just a thread discussing how wiring a GP solenoid wrong can damage a diode in the pcm. I'll see if I can find it. Perhaps a previous owner wired it incorrectly.
I never started a thread on this, I bought my truck for dirt cheap and this is why. Guy tried multiple glow plug relays to no avail. I also tried a new glow plug relay to no avail. Then went and looked up how to wire gpr to push button, there's a forum on it. Followed those steps wired it up and my glow plugs now work. Oil temp sensor can also make glow plug relay not work of it thinks oil temp is above live 136 I think.
@Sous recently posted in a thread that showed how a switch can be wired in, but it was in a different topic thread. I think I accidentally posted it an excursion thread but probably deleted the post
oops, i think I misread t-woods post...Must be getting tired, disregard what I said
Like sous, I will attach a link to another issue I see a lot when people don't want to spring for the extra $$$ an actual glow plug relay commands over another common relay. This will cause either non-functioning glow plugs, burned-up glow plugs, or fried driver circuits in the PCM.
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