Glow Plug Relay/ PCM

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Dec 31, 2017 | 05:22 PM

akmikek

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From: North Oregon Coast

Glow Plug Relay/ PCM

I just installed a new GPR on a 2000 F450 and when i turn on ignotion i am still not getting power to the large post that goes to the glow plugs? I also get P0380 glow plug system code. When i hook up meter to the negative battery post and small terminals on the GPR, i get 10.5v-11.5v on bothe of the small posts with key on engine off. I get 12.4v on large post with key off and nothing on small posts with key off. I dont see a glow plug module on the valve cover. Any idea why i wouldnt get power to other large post with key on if im getting current to both small posts? Is the small post furthest from the firewall supposed to have power with key on? What else can i do to troubleshoot the glow plug system?

Dec 31, 2017 | 05:27 PM

Walleye Hunter

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From: Douglassville, PA

You shouldn't have current to both small lugs. The one towards the firewall leads to the PCM and gets grounded when the PCM calls for glow plugs to be activated. Power to the one large lug at all times is good, power to the front small lug key on is good. The engine oil has to be cold (I forget what the temp threshold is) for glow plugs to be called for. Is your engine cold enough?

Dec 31, 2017 | 06:22 PM

johnsps250

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From: Northern Virginia

I believe you should be getting 12v if you read from either small post to ground with the key on. The PCM doesn't appear to be providing a ground to close the relay.

Dec 31, 2017 | 09:46 PM

akmikek

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From: North Oregon Coast

Could this be a bad ground going to the PCM? Where is the ground for the PCM?

Jan 1, 2018 | 06:27 AM

timmyboy76

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Mine did the same c thing. After 2-relays I thought v were bad, it was evident, something want right. Conclusion for me, was to run a write from the ground side of relay, to a switch, then to ground. Have to manually operate the system... Beats a new pcm.... Use the gpr-led mod so you know that the gor's are wiring and that you don't v leave the switch, on.

Jan 1, 2018 | 06:27 AM

tjc transport

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From: Marlboro Mental Hospital.

over 110 degrees engine temp the glow plugs do not work.

Jan 1, 2018 | 11:07 AM

johnsps250

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From: Northern Virginia

Quote:

Originally Posted by tjc transport

over 110 degrees engine temp the glow plugs do not work.

I agree with the above, I am not sure exactly what parameters can disable the GPR, I'm sure someone will chime in with that info shortly. But I would check those parameters before condemning the PCM and using a work around. Could be as simple as a bad temp sensor.
If all else fails, a switch in the cab to manually provide a ground will work also.

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Jan 1, 2018 | 02:06 PM

Hussler

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From: Medford Oregon

Quote:

Originally Posted by akmikek

Could this be a bad ground going to the PCM? Where is the ground for the PCM?

There is not a actual ground wire going to the PCM, physically. One of the small terminals on the GPR goes to the PCM internal electronics and it grounds the wire to activate the GPR.

Quote:

Originally Posted by akmikek

First you need to troubleshoot with the engine cold. And then you probably only have 45 seconds or so to measure voltages before the PCM deactivates the GPR. Gota be quick! You can recycle the key and do it again as long as necessary, just don't start the engine and get it warm-hot. I see you're in Oregon coast so it's not too cold, compared to other regions this time of year.

You are not really getting current from both small posts. With key ON one small post will be at battery voltage at all times and the other will be the same, it's just a coil of wire until the PCM pulls that line to ground during the GPR cycle thing.

Jan 1, 2018 | 02:23 PM

#10

akmikek

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From: North Oregon Coast

Thanks for all of the responses. It looks like i will do the switch/LED mod? Does anyone know of a DIY or diagram for this mod? I couldnt find anything online? I would assume that i remove the PCM lug off the small post nearest to the firewall and run a wire from a good chassis ground through a switch to the small post the PCM lug was on? Could i just leave the PCM wire on and add a wire for a switch? If i use a switch with an LED will it shut off automatically once the relay shuts off? What about a push button switch so there is no risk of accidentally leaving it on?