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Interesting glow plug relay issue

2K views 16 replies 4 participants last post by  NoRalPh 
#1 ·
So, drivers side post on the GPR read nothing with the key on so I replaced the relay. Put the new relay in and now the constant post reads whatever the battery is like it should, but the other one reads a steady 23 volts... what would cause this?
 
#4 ·
I don't see how that could possibly happen, I would recheck your meters settings. There simply IS no source for that much voltage (you could Series the two batteries but that would fry all the electronics).

So, there's something else going on here. Those two, Lg terminals, simply get connected together with the solenoid energized. With the contacts in a new GPR you should read identical voltage on them at that time (it will be Lower than the static, 12.3v, because of the load of the GPs). I would expect to see @11v but certainly nothing over 12 could happen...
 
#8 ·
Ok. Retested it when I got off work tonight. 39°F outside tonight. Truck hadn't been running for 9 hours, so the glow plugs *should* have come on. No relay click, 0 volts on the glow plug post. So what next? I'm assuming a trigger wire or pcm issue? Any other reasons why a brand new relay wouldn't be working properly?
 
#9 ·
Find out if there's everything you need at the GPRs connections.

Test it by removing both sm wires from the relay and determine which one has 12v in it with the key ON. The wire that Does NOT is connected to the PCM and is what it uses to activate the GPs by providing a path to GROUND. Use a meter and connect one side of it to the battery (+) and the other to the PCMs wire. When cold, and it should be using the GPs, you should see 12v flowing through the meter (make sure it's in DC, test it first across the batteries terminals). Depending on how cold it is you should see that power flowing there for from 30-120secs.

If the PCM doesn't supply that path-to-Ground like it should, then either it Can't (bad PCM or wiring) or, it doesn't Think you need them when it Should (bad EOT or wiring to it).

If you have what you should in those sm wires (12v in one and Ground supplied in the other, when disconnected) and it doesn't "click" with that, then the GPR must be bad...
 
#11 ·
I'd bet your ground wire to the ECU is bad. Quick fix is to run a momentary switch from the GPR to ground so you can "activate" the GPs manually on demand.

EOT you need a scanner to see the temp, I've never heard of one going bad though. Are you getting the "WTS" light on the dash?
 
#13 ·
If the sensor has a fault, and there's a code for it, the PCM will ignore the sensor and use a value of 212F while running, and -29F for starting.

EOT sensor values chart:

 
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