glow plug relay
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Joined: Oct 2011
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glow plug relay
got stuck up on the moutain the other day truck wouldnt start 25 degrees. When i got down the moutain it started right up so i knew i had a problem with my glow plugs. replaced glow plugs and relay. My truck started up but the temp is around 90 degrees. tested relay to make sure it was working had 12.5 vots on hot side but nothing on other post with key on or off. if the engine is hot already will the relay still tun on to heat glow plugs even for a second or will it only turn on if engine is cold and needs to be heated?
Postmaster
Joined: Jun 2009
Posts: 2,566
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From: Monroe/Ellensburg, WA
No......
I have a LED attached to the hot side of my GPR and when my engine is hot, It will not turn on at all...
Check the relay again when the motor is cold before throwing it away...
I have a LED attached to the hot side of my GPR and when my engine is hot, It will not turn on at all...
Check the relay again when the motor is cold before throwing it away...
Fleet Mechanic
Joined: Oct 2006
Posts: 1,386
Likes: 1
From: Spokane, WA
if the engine is hot already will the relay still tun on to heat glow plugs even for a second or will it only turn on if engine is cold and needs to be heated?[/quote]
Don't know at what temperature the GP system turns off, but if the engine is hot or up to full temp the GP system should not be needed for starting.
Don't know at what temperature the GP system turns off, but if the engine is hot or up to full temp the GP system should not be needed for starting.
Post Fiend
Joined: Dec 2010
Posts: 10,121
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From: Orrville, Ohio
My understanding is that if the PCM sees an engine oil temperature above 140 degrees it will not engage the GPR.
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New User
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thanks guys for the input. i checked it this morning with the engine cold and the relay is now getting power to both post. so must have been because the engine was already hot or above that certain temp it doesn't turn on which makes sence.
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Postmaster
Joined: Jun 2009
Posts: 2,566
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From: Monroe/Ellensburg, WA
Glad you checked it cold. PCM takes oil temp into consideration. If there is no need for glowplugs, they don't come on saving them and the relay from working when they don't have to.
Elder User
Joined: Aug 2009
Posts: 869
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From: Michigan
the best way I have found to check the gpr is to test it with a cold engine and a volt meter. turn the key on and check the 2 small posts if you have 12 volts there that means the relay is in fact on. now that you know for sure the gpr is on, check the volts across the 2 large terminals. with the relay on there should be 0 volts or a very small fraction of 1. any reading you get during this test is the amount of volts that are NOT getting to the glow plugs. any significant reading and I would place my order for a new GPR.
Lead Driver
Joined: Oct 2010
Posts: 5,132
Likes: 45
From: Columbus, Oh
the best way I have found to check the gpr is to test it with a cold engine and a volt meter. turn the key on and check the 2 small posts if you have 12 volts there that means the relay is in fact on. now that you know for sure the gpr is on, check the volts across the 2 large terminals. with the relay on there should be 0 volts or a very small fraction of 1. any reading you get during this test is the amount of volts that are NOT getting to the glow plugs. any significant reading and I would place my order for a new GPR.
Fleet Mechanic
Joined: Oct 2006
Posts: 1,386
Likes: 1
From: Spokane, WA
Originally Posted by Ken_C 
the best way I have found to check the gpr is to test it with a cold engine and a volt meter. turn the key on and check the 2 small posts if you have 12 volts there that means the relay is in fact on. now that you know for sure the gpr is on, check the volts across the 2 large terminals. with the relay on there should be 0 volts or a very small fraction of 1. any reading you get during this test is the amount of volts that are NOT getting to the glow plugs. any significant reading and I would place my order for a new GPR.
Times Two -- I agree
the best way I have found to check the gpr is to test it with a cold engine and a volt meter. turn the key on and check the 2 small posts if you have 12 volts there that means the relay is in fact on. now that you know for sure the gpr is on, check the volts across the 2 large terminals. with the relay on there should be 0 volts or a very small fraction of 1. any reading you get during this test is the amount of volts that are NOT getting to the glow plugs. any significant reading and I would place my order for a new GPR.
Times Two -- I agree
Elder User
Joined: Aug 2009
Posts: 869
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From: Michigan
If you feel like going through 300 pages of replies im sure some variation of this method is probably in there somewhere. that post is too dang long i tried to find it in there but got bored looking.
Lead Driver
Joined: Oct 2010
Posts: 5,132
Likes: 45
From: Columbus, Oh
I was looking at it earlier and there is a version of it, but I personally feel like you spelled it out a lot better. If I wasn't on my phone, I'd send you some reps