Glow Plug Relay Problems

[mjonesjr]

I am having trouble with my glow plug relay. I have put a new relay on the truck, however I am still not getting any action to my glow plugs.

The factory wire that is supposed to trigger the relay is getting 12v (battery voltage) when the ignition is turned on. It is on the "S" terminal of the relay. Should it be on the "I" side of the relay?

[mjonesjr]

I am getting 12v with key on on both the small red and small brown wire going to my relay. I am not getting any voltage to the glow plugs.

If I ground the relay on one side straight to battery, it will hum and put voltage to the to the glow plugs.

[mjonesjr]

I traced the brown w/ red or orange stripe wire from the relay to the PCM and it ohm'd out good.

I read that if you disconnect the oil temp sensor that it will activate the relay for the total of 2 minutes. Well I tried that and the relay never went active.


Any ideas?

[mjonesjr]

Anyone have any ideas? I would prefer not to pay the dealership $70 to diagnose it.

[jesilvas]

ummmm, I can show you a picture, or take one. Hang on let me look.



AIH relay on bottom. GP on top.

[Boss.Hoss]

The schematics show a Red wire with a green stripe that should be hot in run or start (fed from 30A fuse #22 in under-hood fuse box). The other small wire is a Purple wire with an Orange stripe that come from pin 101 in the PCM. That wire is how the PCM grounds the relay to turn the glowplugs on for whatever length of time it wants. You should see ZERO volts coming from the Ppl/org wire from the PCM whenever the glowplugs should be on (first 2 minutes of ignition being on I believe).

Do you get a WTS light? (wait to start)

[mjonesjr]

Originally Posted by Boss.Hoss

The schematics show a Red wire with a green stripe that should be hot in run or start (fed from 30A fuse #22 in under-hood fuse box). The other small wire is a Purple wire with an Orange stripe that come from pin 101 in the PCM. That wire is how the PCM grounds the relay to turn the glowplugs on for whatever length of time it wants. You should see ZERO volts coming from the Ppl/org wire from the PCM whenever the glowplugs should be on (first 2 minutes of ignition being on I believe).

Do you get a WTS light? (wait to start)

I have traced the purple/orange wire back to the PCM and found it to be good solid wire.

I get the wait to start light, but nothing happens to the relay.

[Boss.Hoss]

if that wire ohms out okay (has good continuity and isn't broken internally) then obvioulsy the PCM is then not doing it's job. I'll dig around and see if i can find any documentation on how the PCM determines when to run the plugs... I don't know if there are any other sensors or wires that could cause the PCM to never fire the plugs for at least a few seconds when you first power the truck up...

EDIT:

Just found this:

"Glow plugs are used to improve cold engine starting and to eliminate White smoke. The Powertrain Control Module (PCM) uses the Engine Oil Temperature (EOT) sensor and Barometric Pressure (BARO) sensor to determine low long the glow plugs will be on. The PCM energizes the glow plugs longer if engine is very cold or if barometric pressure is low at high altitudes."

Looks like it uses BARO sensor as well as EOT sensor... Not sure if that helps us any though...

EDIT 2:

This guy had similar problems and found a bad connection at the plug near the valve cover, granted this was on a superdude, but it shows you should check all connections between the GPR and PCM, including the one at the PCM....

PCM not activating the GPR

[mjonesjr]

Originally Posted by Boss.Hoss

if that wire ohms out okay (has good continuity and isn't broken internally) then obvioulsy the PCM is then not doing it's job. I'll dig around and see if i can find any documentation on how the PCM determines when to run the plugs... I don't know if there are any other sensors or wires that could cause the PCM to never fire the plugs for at least a few seconds when you first power the truck up...

EDIT:

Just found this:

"Glow plugs are used to improve cold engine starting and to eliminate White smoke. The Powertrain Control Module (PCM) uses the Engine Oil Temperature (EOT) sensor and Barometric Pressure (BARO) sensor to determine low long the glow plugs will be on. The PCM energizes the glow plugs longer if engine is very cold or if barometric pressure is low at high altitudes."

Looks like it uses BARO sensor as well as EOT sensor... Not sure if that helps us any though...

EDIT 2:

This guy had similar problems and found a bad connection at the plug near the valve cover, granted this was on a superdude, but it shows you should check all connections between the GPR and PCM, including the one at the PCM....

PCM not activating the GPR

I appreciate the info.

From my readings on this this week, I read that if you unplug the oil temp sensor the PCM will activate the GPR for the full 2 minutes. When I did this test, the PCM still didn't activate the GPR. I don't know if I read it wrong or what.

With the oil temp sensor unplugged, the truck will not start at all; it will just crank.

I have checked all the connections at the GPR, oil temp sensor, and what I think to be the Barometric sensor under the steering column and all are making good contact.

I wish there was a way to check the sensors without having to let the truck sit at a shop overnight so they can hook it up to a computer and I don't want to spend the $360 right now for a program right now so I can do it at home.

[mjonesjr]

I did a little wire tracing today.

The purple/orange wire at the GPR ohmed out to 3 wires at the PCM connector. Those wires seem to be ground wires.


The purple/orange wire is grounded when the key is off and the PCM puts 12v to it when the key is turned on.



I need to pull the harness apart on the engine now to see if I have any wires burnt together.