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Glow plugs inoperative

2K views 5 replies 3 participants last post by  bismic 
#1 ·
I had one bad glow plug, so I changed all plugs, both harnesses and glow plug module. Now I have no glow plugs working.
 
#2 · (Edited)
This might be helpful:

The GPs are activated by the PCM based on BARO, ECT and EOT to determine GP on-time.

The command to the GPCM is over a datalink, if the tech can command them on (KOEO output test) then the GPCM theoretically is working correctly.

The next thing to know is, are the BARO, ECT and EOT sensors reading correctly? This is EASY to check on a cold-soak start (engine off for at least 12 hours) by using a scan tool to view those three parameters. Obviously, EOT and ECT should match IAT1, IAT2 (ambient temp), and TDT (transmission temP); and BARO should be 14-15 PSI at sea level (the barometric pressure at various elevations is easily found through an internet search).

I believe that if the oil temp is reporting over 131 *F, the glow plugs will not be turned on.

Otherwise your options are:
1. bad electrical harness
2. bad GPCM
 
#3 ·
Another troubleshooting procedure:

Both plugs on the Glow Plug Control Module have leads that supply the amps/power to all the glow plugs ( pin#'s 1,2,6 & 7 of both GPCM connectors feed to each bank of GP's). Both GPCM plugs have a #10 black wire with orange strip/tracer. These are the main 'power' wires coming from the passenger battery. They actually tie together with "fuseable links" to a #6 red battery cable to the passenger battery. You can clamp your amp meter over the red cable and see the total amp draw going to the GPCM with KOEO. You can also verify the GPCM is receiving B+ voltage at pin#9 (small dia. solid red color lead) of black connector on GPCM. It should have B+ voltage with KOEO(Key On Engine Off).
The glow pug wire harnesses have quick disconnects at top side of valve covers and you could disconnect them and conduct ohm readings of each individual glow plug, as well as test for any open circuits.

You can also check for input, continuity and any shorts between the 2 input feeds from the PCM to the GPCM 'green' connector: The PCM provides input to GPCM thru PCM pin#'s 3(GPE) and 17(GPD) of J1-C2 connector to GPCM 'green' connector pin#'s 8 and 9. So, to recap:pCM #3 goes to GPCM green #8 and PCM #17 goes to GPCM green connector #9.

These check points should verify the functionality of the Glow Plug operation.
 
#4 ·
No update ..... ?
 
#5 ·
Update? Why do that? Just because you spent your time trying to help doesn't mean they should update to let you know your time is appreciated.

Yes, I'm being sarcastic. OP, it sure would be nice to provide some closure for those that have taken time to share their wealth of information.
 
#6 ·
Sometimes you just have to shake your head ...............
 
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