Working on a 2001 7.3 and I think I may be having an issue with the control module/relay for the glow plug relay.
Wondering if somebody has the schematic for this device.

Relay and glow plugs are new and seems to work when I apply 12 volts and I can measure voltage across the relay and see a voltage drop on the secondary side of the relay. Relay does not appear to cycle like its supposed to when the key is turned.

A schematic would be very helpful.

Thanks....Kevin

 

I think I have lost the negative for the glow plug relay and need a wiring diagram or schematic that would show the route of term for the negative and or the positive control wiring.

Thanks....

 

Would love to help but you haven't said which system you have. Do you have the Glow Plug Control Module or the more traditional relay pairs?

Here is a photo of the standard set up...

 

Got the traditional relay pairs... as shown in the picture. If I had a schematic I think I could trace back the harness and possibly find a loose/broke wire.

Thanks,
Kevin

 

Maybe this will help....

The way your system works is the glow plug relay has 12v power on the high and low side at all times. The ground for the low side runs to the PCM which remains open until the PCM decides to provide a ground. At that point the relay should energize and provide power to the plugs.

Here are some diagrams that will help. It says 1999 but should be the same for 2001 (they didn't change things until '02 model year...)

 

One more thing in case it helps...

If you suspect a problem with the relay, then you can swap it out with the AIH relay and see if that works. The AIH relay hardly ever gets used so it's likely to be in much better condition inside. Lot of guys have actually deleted the Air Intake Heater element so their relay just sits there as a spare. My daily driver doesn't have the heater so I plan on using the relay as a spare if/when the time comes....

 

Thanks for the info..was exactly what I had been looking for! this should help a lot!!

As for the condition of the relay I know it works great because I have bench tested it with 12 volts and an ohm meter and found it works flawless. I can find a standing voltage like you mentioned in the earlier post but as you mentioned I am not finding the negative as I need to energize the coil as it should when needed. I had thought that it was cycling the positive to energize but it sounds as though it is cycling the negative on a standing positive. I may have something acting up in the control module of the truck. This should help to confirm the wiring issues and narrow it down.

Again thanks for the schematic info....

Kevin

 

Correct.

I decided to wire a simple switch on the control wire between the relay and PCM. This gives me the option to disable the glow plugs for times when I am using my scan tool or during maintenance (such as working under the valve covers etc.) Another possible benefit could be if the batteries are too weak to allow the engine to start....under those conditions it's sometimes helpful to disable the glow plug relay so there is more voltage for the PCM. Once the PCM sees around 10 volts then it will allow the IDM to fire and start up the engine.

 

So I have had a chance to review the schematics for the glow plug relay. I have trouble shot the wiring all the way back to the PCM and it appears that I am not getting the output from the PCM to fire the glow plug relay.

So I am guessing either I have a burnt channel for that output or I have a corrupt PCM.

So the question is.... could I have the PCM reflashed and possibly fix my problem or should I just replace the entire PCM considering I will have to pay for a flash either way....

Any suggestions?