I wanted to share my trouble shooting and final outcome experiences with all of you in case you Excursion owners come across the same problems I did if a "Service Engine Soon" light illuminates on your dash.

First off, my Excursion is a 2000, 7.3L diesel.

Last week the "Service Engine Soon" light came on the dash panel. When it did, the truck had been outside during a three day heavy rain storm. I accidently started the truck before the "Wait to Start" light went out. The truck turned over with the A/C on full blast. I must have been in a complete daze to not remember to turn the air off and wait for the glow plugs to warm up. I am not saying that these issues caused the light to come on, however I do think that this combination contributed to the problem and it is too coincidental.

I thought that maybe I just needed to clean out the injectors at first so grabbed a full tank of diesel and injector cleaner, to no avail. I read through my Hanes manual and found that the glow plug system could be buggered up but I needed to be sure. I figured I could get a quick, free diagnosis done at O'Reilly's that night to figure out the problem. After hooking a meter up, the codes came back for bad glow plugs on cylinders 2,4,6 and 8. This looked to be an obvious electrical problem considering four plugs went out at the same time. Highly unusual for all four to go out. Think of the odds! O'Reilly's quoted me almost $80 for one glow plug. That didnt sound right so I held off doing anything and sought further diagnosis.

I brought it to my local shop (Yost Automotive in Austin) and had them troubleshoot the glow plug system from the glow plug relay to the valve covers using an ohm meter. They told me, after testing the system, that they couldnt find anything wrong and would have to remove the valve covers to inspect the rest of the glow plug wire harness.

I decided that since the problem was either the glow plugs themselves or the wire harness, based on their diagnosis, I ordered two valve cover gaskets (since the old ones were wet and tired) with wire harness and eight new glow plugs. I figured since the shop had to pull out the turbo cold air intake to get to the valve covers, I might as well as have both valve cover gaskets and all eight glow plugs replaced.

I brought the truck back in to complete the job yesterday and after having all these parts replaced, the "Service" light went out. Well it wasnt but half a mile down the road when the "Service" light went back on. Here's where it gets intersting and annoying...

So remember when the shop was troubleshooting the wiring to the valve covers? Well it turns out they tested the wiring but did not test the glow plug controller. Put simply, this little beauty is what sends electric current to the glow plugs in order for them to heat up. There are two plugs on the controller/relay. One of these plugs for the left bank of the engine "went out" causing the "Service" light to come on the dash, the four plugs to fail, and for the meter to get the faulty glow plug codes. So after having the valve cover gaskets replaced, the wiring harness for the glow plugs replaced, and the glow plugs replaced it turns out that all this work could have been avoided had the damn glow plug controller/relay been tested first. It is possible that the glow plugs failed causing a short in the controller but to me, that is unlikely.

So here is what a glow plug controller is:
http://www.rockauto.com/catalog/moreinfo.php?pk=930074

This controller sits on top of the engine, practically in between it, behind the "Powerstroke" engine cover on the right engine bank. It may be discolored from its natural silver coloring, due to regular disel soot, oil and gunk, and may appear blackish in color. One plug is green, the other black - in some cases one plug may be brown. This piece does not take long to replace. From what I can tell its simply a few quick electrical disconnections and removing two screws. There are no other pieces to remove to get access to it.

Now I am pretty happy that my 13 year old truck has fresh valve cover gaskets on them and new glow plugs. Its doubtful the previous owner had any of them replaced. Its not regular maintenance but its expensive. I did purchase all my parts through Rock Auto. They are by far the cheapest with glow plugs coming in between $5 and around $10 for Motorcraft plugs. Dual valve cover gaskets with glow plug wiring harness was around $120 for two. For what really caused the problem... glow plug controller ,cost about $167.

So if you get the "Service Engine Soon" dash light for a 7.3 diesel, remember that it more than likely has something to do with your glow plug system. Be sure to check the glow plug controller first before tearing into the valve covers. Otherwise you will be spending a lot of time tearing down turbo intake lines and other odd equipment just to get to the valve covers for a problem that can be easily fixed from atop your engine.

 

First, welcome to FTE!

Second, please don't let my post perturb you or make you roll your eyes. Just trying to help.

No harm in that at all. I do that all the time with all of my 7.3's. As long as it isn't cold out, or if your engine is warm, you'll be ok.

It did not contribute to your problem. It was just coincidence your GPCM chose that moment to go out.

Please don't do that. PSD HUEI injectors can be finicky and generally speaking, "injector cleaners" shouldn't be used in your PSD. The best way to clean out your fuel system is to run a couple tanks of bio-diesel through the system. Just make sure to change the fuel filter after you do.

I'm surprised O'Reilly's had a code reader that reads the 7.3L. Usually their generic readers don't have that capability.

It's too bad you didn't find FTE first. We could have saved you some time and money because depending on which code you had, it was most likely one of two very common issues.

Whenever you have one complete bank out, the two most common causes are the UVCH (Under Valve Cover Harness) or the GPCM. In your case it was the GPCM (Glow Plug Control Module).

Very common problems we here at FTE would been happy to help you diagnose and fix.

Rock Auto is a good source for parts. Tousley Ford parts department Tousley Ford Parts Depot and Riffraff Diesel Riffraff Diesel Performance Parts | Ford 7.3 diesel | 7.3 powerstroke | Ford Powerstroke | 7.3L Powerstroke Parts are two more great options for OEM parts.

Not quite correct. There are TONS of different codes that will set the SES light. The P0683 GPCM communication error code is but one on a list of thousands.

But what I think you probably meant was, IF a person gets any of the glow plug error codes (P0671 - P0678) or the P0683 code, don't assume it's the glow plugs, correct?

Stewart

 

I just replaced my GPCM two months ago, after getting code for glow plugs. An hour of troubleshooting and I narrowed it down to GPCM. I am in Austin area as well. I have a Ford computer (for the 7.3) and a good friend here in Austin that is a Ford diesel mech. As Stewart stated, we are happy to help, collectively have all the answers you would likely EVER need and in many cases have tools and friends to do the work ourselves. Welcome to the community! Now come to us first next time!!

 

I had the 'Service Engine' light last spring and had to replace my GPCM. Last week I had the light come on again, and this time it shows a #2 glow plug. Well, I need to have the wedges put on the UVCH and the injectors re-ringed, so I guess I will be having all this done in the next week or so. While I am there, I'll replace all the glow plugs.

 

Re-torque the rockers while you're there.

Stewart

 

Thanks. Will do!

 

mrbing..

what code was it showing??

 

Guys ... looking for some guidance ... SES light on, had tested at autozone, error code P0678, which according to them is glow plug circuit ... open, short or faulty glow plug ... cylinder 8. So, what do I check first and how? Thanks for the help on this.
2003, 7.3L, 98,000 miles.

 

You need to get it on a computer that can 'buzz' each injector and do a proper glow plug check. It could be your glow plug control module. Up on the passenger side of the engine in between cold pipe and ac compressor, the silver thing in the middle.

The Xs have a glow plug module, not a glow plug relay. Also, you said it showed a problem with the #8 glow plug, or did it say 'low compression' on #8?? If it said 'low compression' on cylinder 8, most will show that code since Ford replaced the camshaft position sensor with one that is not suppose dto fail. If it was #8 glow plug, I bet you have a problem with the module.

 

If it was the GPCM, the codes would show one complete bank as being out.

Scuba, was that the only code you retrieved?

Stewart

 

Stewart, when scanning mine with my Innova scanner, it said "GPCM Fault". Prior to getting home, I was on the road and took it by Auto Zone(forget the name of the scanner he used) but he said that it showed 3 glow plug faults, numbers 2, 4, and 5. I thought that was funny. When I got home, mine showed the GPCM. I wonder if this differs with the brand of scanners? Is that possible you think?

 

Guys, thanks for the prompt responses. I will have it tested again but the guy who did it reported only one code P0678 which is reportedly glow plug number 8. Said nothing about compression. Starts and runs just fine. SES light comes on when the ignition is turned on, then blinks out, then comes on and stays on. All other systems appear to be working just fine. I'll have it retested tonight on the way home. More once I know it. Thanks again.

 

Hmmm, I dunno. But by the very nature of how the GPCM works, if the cause of the glow plugs not working is due to a bad GPCM, then either both banks would be out, or one bank would be out, according to what I've read here, as well as my own personal experience.

Stewart

 

had it re-tested. Only one code comes up .. P0678. I believe this indicates GP #8 or the wiring to this GP. GPCM should be OK. So, can I just put an ohm meter on this GP from the connector block to a good ground? What should the reading be? How isolate the GP from the harness wiring to be sure which of the two is really bad? Other ideas? Thanks.

 

Thank you for the thread. The SES light on my 2001 F250 7.3L Super Duty came on so I got it checked at AutoZone. They gave me a readout of error codes P0672, P0674, P0676 and P0678. Per the info given in this thread, I pulled, tested and finally replaced the GPCM. The SES only lights up during the lamp check now.

Steve