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New Glow Plug Relay will not turn off

P

pgguru

Recruit
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Location
Hamilton Ontario Canada
So I finally Got a new Glow plug relay because the wife never remembers to use the manual one. So I install it and now I get glow when ever the key is on even after it starts? I checked the harness and there is 12V on 2 wires and nothing on the third when ever the key is on.

Does any one have any ideas for me?
I've cleared the codes 29 glow plug relay but it still comes back
I've disconnected the battery for over an hour still the same problem
 
Could be something wrong with the ECM, ECM controls glow cycle.
On the other hand, how is your manual glow wired in, could it cause the glow controller to stay activated??.
 
I think?? Dont hold me to it.
ground
ECM signal
Light

Does the light stay on for aslong as key is on?
Or are the plugs cycling then shut off after start up? if yes thats normal
 
Heres a diagram showing the wiring for the glow plug system for a 95.
Click on the pic to make it bigger.

glow plug diagram.jpg
 
Yes its connected correctly. I started getting a SEL with code 29 Glow Plug Relay even though I have not had one installed for a year. with the Key on I have 12V on yellow and Pink Wires even after I start it.
 
What color is your new glow plug relay(should be black, if it's grey it's the wrong one)? I believe I remember years back somebody put a 92-93 relay in a 94+ truck and it did this.
 
The plugs are different between 93 to 94 &^. You would have to force the plug to fit. I think the 93 type is a 4 wire 94 &^ is 3 wire.
 
Burning oil said:
The plugs are different between 93 to 94 &^. You would have to force the plug to fit. I think the 93 type is a 4 wire 94 &^ is 3 wire.
Click to expand...

Have you tested for a stuck relay? Course the lamp would stay on key off and your batteries would quickly die.

Just one less wire in the newer model years connector - they are identical otherwise and will plug into all years with ease.

I doubt color matters as they all turn black with oil and soot... :D Seriously I think I have seen both colors for 1993. Best to count the actual pins on the controller to be sure. 3 pins is for 1994+ and 4 or more is earlier years. 1988 for example doesn't have an internal temp sensor like the 1993's do and uses a wire to a switch on the passenger head rear. 1994+ is all ECM controlled.

You will get a code for a missing relay as the ECM watches the glow plugs to see if the relay is working as commanded.

Do not run the engine very long with the glow plugs stuck on. The injectors will blow the powered red hot plugs in half. It is messy after that...

Best way to test the 1994+ relay is to check the ECM signal and see if it changes in the plug. It will have 5-12V to turn the relay on or get pulled to to ground by the ECM. I forget exactly. But backprobe the yellow center wire on the glow plug harness and check for voltage. Key on it should have the 5+V and then turn off to 0v after the glow plug timer is up. Backwards also would work depending on how GM did it. (I suspect the first getting 5+ volt reading is the correct way.)
 
The one's I have seen have been different. Ive done my share of DS4 to DB2 conversions and you have to go to the old 93&v relay. Each time I had to depin the connector and put the correct/matching one on.
My 2 cents.
 
I've Checked that the relay unlatched with the key off so its not stuck.
It seems to me that there should not be 12V on the Pink wire?
I know last year I was looking to see if I could use the Trucks Signal to run my relay but it would not work.

I am going to see if I can find a new Computer and try to swap it... If I find one I hope it works.
 
pgguru said:
I've Checked that the relay unlatched with the key off so its not stuck.
It seems to me that there should not be 12V on the Pink wire?
I know last year I was looking to see if I could use the Trucks Signal to run my relay but it would not work.

I am going to see if I can find a new Computer and try to swap it... If I find one I hope it works.
Click to expand...

The pink wire is hot with the key on, the yellow wire is powered via the ECM to trigger the glow plugs, and the black wire is the ground.
 
So I have traced the yellow wire to the Computer and cut it to check for it getting power from a short... It is dead and the Computer is sending 12V down it all the time the key is on..
So now I need to find a computer from a 94-95
 
Does the temp sensor send signal to the ECM, if so that could be the error. Or am I stuck in confused land again?
 
Will you could be onto something. When he posted his last I was trying to think what would cause ECM signal to stay on.
 
even is the temp sensor was not sending a signal the truck should run max time.. I think its around 30 seconds of Glow
I'm having a hard time finding a Computer in my area. tomorrow I will check all of Canada
 
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