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Old 12-04-2011, 01:53 PM
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GRP Ground Problem

Please shed some light i read the GPR is controlled by a +12 volt signal (red wire) to the "S" terminal of the relay. The ecm also controls a relay that provides ground (brw w/blktracer) to the "I" terminal of the relay. So if it is 50 F how long should the relay stay energized.

The problem is if i check across the big terminals the terminal to the glow plugs does not have 12 v o it until i ground the "I" terminal then the relay engages. SO i am trying to figure out if i have a bad ground circuit, If i measure resistance from "I" to ground i see apprx 128 ohms and when the ignition swith is turned on the resistance goes infinite. How do i find the "ground " relay and know if the pcm is telling it to energize or not?

A schematic would be great.
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Old 12-04-2011, 02:25 PM
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Coupla things.....

First, kinds hard to know what schematic you need without a year

Next, I'm gonna take an educated guess from watching my GPR Led on my gauge set, and say at 50 degrees maybe 45sec. The PCM uses the EOT (Engine Oil Temp) to determine how long to keep them on.

So, inside the PCM the path to ground is supplied, probable through a solid state device rather than a relay, for as long as it wants the GPs on. If it's NOT, then either it doesn't "think" it should because the EOT is wrong, there's something internally wrong with the PCM, OR the wiring/connections are bad.
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Old 12-04-2011, 03:58 PM
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2003 and from what you describe it sounds entirely possible it is turning it off after the first attempt and anything afterwards it is already sensed the temp
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Old 12-05-2011, 06:25 AM
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I'm not sure what you mean here.... Are you saying the relay activates on the first attempt, then not again if you immediately retry? Or is the second attempt after you've driven it and restart a short time later? Remember, the WTS and GPR are in No Way connected. That is, once warmed-up, even though the WTS comes on the PCM does Not activate the relay.

Here's a basic schematic.
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GRP Ground Problem-2002wiringdiagram.jpg  
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Old 12-05-2011, 10:23 AM
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Quote:
Originally Posted by NoRalPh View Post
I'm not sure what you mean here.... Are you saying the relay activates on the first attempt, then not again if you immediately retry? Or is the second attempt after you've driven it and restart a short time later? Remember, the WTS and GPR are in No Way connected. That is, once warmed-up, even though the WTS comes on the PCM does Not activate the relay.

Here's a basic schematic.
The relay did not activate either time. I am waiting for it to stop raining today and try it again. It was 60 ish in cinci yesterday so i am wondering if the pcm shut it down based on the oil temp. I also plan to test the connections them selves.
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Old 12-05-2011, 11:18 AM
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I don't know what the parameters are that the PCM uses for activating the GPs, but it's certainly over 60 before it doesn't use them at All....
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Old 12-05-2011, 12:44 PM
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Checked today stone cold and no reading, once the rain ends i will check the connection from the gpr to the pcm.
I guess the next thing could be to check the oil temp switch and last replace the pcm.
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