I have read and seen videos of how to test a GPR with a voltmeter, I don't have one, here is what I did: I took my handy test light, and tested the positive side of the relay, there is power. I then tested the glow plug side of the relay, there is no power, which should be correct. I then turned the key on to activate the relay and tested the glow plug side and still not hot, which is a problem, right. With the key on, the glow plug side should be hot until it cycles off after 2 minutes, correct? I am correct to say that my relay is not working and a new one is needed? Thanks for your input.

 

Yes, sort of.

Did you get illumination on the signal wire? It may not be the relay. You can ground the signal wire using the test light and you can ground the "Ground Terminal" to activate the Relay. Keep in mind ONLY to use (-). The GPR is ground switched via the PCM.

But, that in and of itself does not prove the relay to be functional under a load.

The GP Cycle is dependent upon EOT and AIT. It can be as little as 0 seconds or as long as 120 seconds.

 

Sorry for sounding foolish, electrical is my downfall, so what you are saying is that my method does not really determine if the relay is bad, correct? Sounds like I need to purchase a voltmeter and measure the two lugs to see if there is a drop in volts, correct? I was having cold start issues when I was hunting last week, it was in the 30's, got home, in the 40's started no problem.

 

any time you cycle the key you should hear an audible click every time as the relay will engauge a very brief moment (at least mine does) when the WTS light comes on, if this click sound is not heard check for your WTS light (it should be on the same circut IIRC) if that does not light check your fuse (i think its #36 or something like that IN SIDE the cab fuse box location...) it may be bad even if it looks good I have had fuses go bad on me...

 

I was able to borrow a voltmeter, and I believe determined that the GPR is bad. On the positive lug, I got 12 volts, I turned the key on and got 0 volts on the glow plug side.

 

But is it getting a signal to the relay (the small wires, and remember it is the ground that is switched for the control circuit)?

 

Ok, not sure where to go now, I put the positive lead of the voltmeter on the hot lug and put the negative on glow plug lug and turned the key on, the voltage remained the same as when it was only on the hot side, so this tells me the relay is working. I them turned the key on and put my test light on the brown wire coming from the glow plug side, shouldn't that be hot when the key is on?

 

Did some more testing on the small terminals, neither are hot with the key off, the one at the 5:00 o'clock position is hot with key on. The small terminal with the orange wire at 11:00 o'clock is never hot, is that normal? Are the wires on the glow plug side supposed to look like they do. It seems as though the relay is not getting power to it.

 

To test the GPR on the control side (the small lugs). They should both be hot unless the GP is commanded to be on - then one should be hot, and the other should read a ground. The control coil inside the relay has 12V supplied to it on one of the small lugs all the time, and the PCM sends the other side a ground signal to energize the GPR. When you see 12V on both sides of the control coil, you are reading the voltage coming from the supply through the coil (normal with a warm engine or the GP cycled off). If the control coil is burned up or corroded (open), then you won't see the 12 volts on one side - ever.

You say you see 12V on one of the small lugs, and 0 volts on the other small lug - that is what you expect to see if the PCM is telling it to come on. If the 0 volts doesn't come up to 12V after two minutes, that would be a bad control coil. If both small lugs eventually come up to 12V after two minutes, that's a good control coil.

Testing the GPR on the power side: Put one lead on each of the large lugs. You should read 12 volts (battery voltage) when the GPR is just sitting there, doing nothing. When you energize the GPR, it should read 0 volts or at least less than one volt. Anything other than those two readings - bad GPR.

When everything is working correctly, these are the two things you should see:

GPR ON: 12V on one small lug and 0 volts on the other - probes on each large lug with zero volts showing.

GPR OFF: 12 volts on each small lug - probes on each large lug with 12 volts (full battery voltage) showing.

 

Check this out: (RIP DTR)

 

Thanks for all your replies and assistance, I was able to determine that the relay is bad. I leave in two weeks for elk hunting, I hope this fixes the cold start. Thanks again.

 

Ok now that he has his problem figured out can I hijack?

I have a GP led. I was under the impression that it would only light if the glow plugs were energized. Is that correct. Mine lights every time I start the truck. I live in Oklahoma and it has not below 60 until today iirc.

 

please see my other post, again the GP relay should only cycle right when you turn the key and then if (when) not needed be off with in 10 or so seconds, meaning your LED should go out (in colder temps it can take up to ~1-2 minutes to cut out) mine (been 60 - 70+ here) usually cuts out with in 10 seconds so values are being given based off my truck


How did you wire up the light? IIRC the light should be on one of the terminals that goes hot (forget which one, will have to search again for info in my thread I think) and then to a ground point (could be a common ground or right to the battery, would also suggest a small fuse like a 7.5 or less in line to the light incase something goes wacky jackie on ya

 

Its always in your best interest to always check the gpr first thing in the morning or a cold engine.
If requirements are met by the pcm the glow plugs don't even come on. I only see my Led light on the first cold start of the day. After that the gpr never energizes.
Takes a couple hours on a cold day to cool off engine to test gpr.


Glad you found the problem. Happy Hunting.

 

So one of you says it always lights for at least 10 seconds but the other says only if it is cold enough. I will pay attention and see how long it stays on .