Hi guys, I'm new here, so if this is posted in the wrong place please move it, and if it's a repeat question, I apologize. I'm dealing with a 2001 F-350, auto.; although far from being a mechanic I can usually deal with most problems. Never had to dive into this truck because for 142K it's been pretty trouble free (other than a blown transmission at 60K ). For the last 10 to 12K the service engine light comes on sporadically, so I went out and bought a code reader. Tells me "Glow Plug Diagnostic Communication Circuit Malfunction". Any tips on fixing this problem??

Although I've never experienced this problem myself, one of my guys that drives this truck regularly says that occasionally it dies at low RPM or idle. Tried everything to have it do it to me, but it won't. Are these problems related??

 

Can you tell us what code you got? Maybe a P0683? Where their any other codes present concerning the GPCM? Different code numbers might have a different priority, so you need to know where to begin the troubleshooting.

Welcome to FTE.

 

What kind of code reader did you get this code with? Could be a few different problems someone else more knowledgeable then me will be along shortly.

 

Thanks for the welcome, and you nailed it, it was P0683. There were no other codes that came up.

 

Innova 3100

 

Here's what you can do to start according to the manual



QB11 CHECK FOR DTC P0683
DTC P0683 is set when the PCM detects an open or short to ground or power diagnostic line.
Possible causes:
open diagnostic line
diagnostic line shorted to ground or power
faulty PCM circuit
faulty GPCM circuit
Perform KOER On-Demand Self Test and retrieve/clear continuous DTCs.
Is DTC P0683 present? Clear DTCs and retest, make sure there is no DTC P0670 present. If DTC P0670 is present, perform DTC P0670 pinpoint test sequence and fix problem before performing DTC P0683 pinpoint tests.
Yes GO to QB12 .
No END test if no further glow plug DTC detected.

QB12 CHECK FOR OPEN IN DIAGNOSTIC LINE
Key off.
Disconnect wiring at PCM and GPCM.
Connect breakout box; leave PCM harness disconnected.
Check resistance between PCM test pin 8 and GPCM test pin 9 at GREEN connector.
Is the resistance greater than 5 ohms? (Typical resistance value is less than 1 ohm.)
Yes REPAIR open in circuit 1277 (WH/LG). RESTORE system. CLEAR DTCs and RETEST.
No GO to QB13 .

QB13 CHECK FOR SHORT TO POWER IN DIAGNOSTIC LINE
Key on, engine off.
Measure voltage between PCM test pin 8 and ground.
Is the voltage greater than 5 V? (Typical voltage should be 0 V.)
Yes REPAIR short to power in circuit 1277 (WH/LG). RESTORE system. CLEAR DTCs and RETEST.
No GO to QB14 .

QB14 CHECK FOR SHORT TO GROUND IN DIAGNOSTIC LINE
Key off.
Connect PCM and GPCM.
Key on, engine off.
Measure voltage between PCM test pin 8 and ground.
Is the voltage a constant 0 V? (Diagnostic signal that is not shorted to ground is a pulse train; 0 V - 12 V.)
Yes REPAIR short to ground in circuit 1277 (WH/LG). RESTORE system. CLEAR DTCs and RETEST.
No GO to QB15 .

QB15 CHECK GPCM CIRCUIT
Install breakout box.
Make sure PCM and GPCM are connected.
Set up scan tool as follows:
choose digital measurement system
choose frequency meter
choose level and change to 6-V scale
connect only the scan tool signal to PCM breakout box pin 8 (GPCM Diagnostic input)
Disconnect EOT sensor connector, (this will maximize the glow plug ON time).
Key on, engine off.
Measure frequency at PCM breakout box pin 8, (take the measurement when frequency stabilizes, approximately five seconds).
Is the frequency in the range of 5 to 10 Hz? (Typical frequency for diagnostic signal with all plugs functioning is maximum 7 Hz. Typical frequency for the signal with one or more glow plugs failed is maximum 15 Hz.)
Yes INSTALL a new PCM. RESTORE system. CLEAR DTCs and RETEST.

No INSTALL a new GPCM. RESTORE system. CLEAR DTCs and RETEST.

 

It could be the famous piece of junk under the valve cover plastic 9 pin connectors have become loose.. Both of mine were loose at 60 K. It is just a matter of removing the valve covers (gaskets are reusable) and fixing the loose connectors. I just a home made shim and placed behind the plastic locking tabs to prevent the connector from coming loose.. It will cause your SES light to come on.. and in some case if the injector pins of affected, the engine will run rough.. Total cost = $0.

 

Thanks for the quick responses guys; you've given me some places to start.

 

I'm having the same code pop up on my '00 Excursion. I've been doing plenty of reading and have it pretty much narrowed down.(praise FTE once again)
I had an idea that we use on aircraft engine systems sometimes. If it is physically possibly to swap the leads off of the GPCM (right bank to left bank)? My thinking is if you could, and the code doesn't change, it's the gpcm. If the code changes to #4(for example), it's in the wires to the gp or the gp itself. Just looking for a quick check before you have to break out the boxes and start disconnecting things. Also would maybe help for some people that don't have access to all the diagnostic tools.
I probably overlooked something totally obvious, so forgive me. I'm just trying to optimize my time under the hood since I usually have 3 kids with the combined age of 11 running around while I'm doing these things.
Thanks,
Aaron

 

Gotta chuckle about your kid thing aaron . Didn't have time to get under the hood today but had plenty of time to drive the truck. First, the thing never died on me; second, I noticed something strange. Seems like if I "short-time" the "wait to start" light the SES light doesn't come on

 

What you say makes sense Aaron, which is of course why it won't work. 2 things to point out are
1) from the manual

Caution

* Connectors are not interchangeable. The system will generate trouble codes if connectors are mismatched. Make sure the harness green connector is plugged into the module green connector, and the black connector into the black header. There is a black stripe on the GPCM housing for visual verification. The stripe should line up with the black connector.
* Do not perform any voltage checks with the engine running: 115V DC at 10 amps are present on the injector circuits.

and 2) If you follow the circuit in the diagram above for the #9 pin on each side, one goes to power, and the other to the PCM. You wouldn't want the power in wire getting signals (probably a ground) from the PCM.

Edit: Vftb, the slow typing title isn't really a joke. I can't reply fast enough if you sneak one in like that. You should know that the little wait to start light on the dash is NOT tied in to the function of the glow plugs at all. It's just a little reminder powered by the computer. The glow plugs come on, and stay on for a determined amount of time, regardless of what that light does.

 

After I pressed "submit" I thought, "wait, it's gotta be getting power through those plugs somehow". Oh well. If we didn't try thinking of new ways we wouldn't be making new discoveries.

Yeah, my wife was walking by and said that was perfect for the fighting boys and our daughter who is always wanting to jump on the trampoline. Gotta love 'em!
Aaron

 

No worries. These types of discussions is what helps everyone learn. I've wondered the same question myself, so if both of us have thought of it, how many more have or will in the future?

Enjoy the daughter on the trampoline. When she gets to be a teenager you'll suddenly remember very clearly what high school boys think about and yearn for the days where your baby girl wanted you to watch her play.

 

Yes, I do enjoy it. I can't tell her 'No'. Probably sounded like I was complaining, but was even smiling as I was picking the for her. As much as I enjoy every day, I dread the day you speak of. I've been told by friends with older kids, it just happens one day, "You go to bed 'a God like figure' and wake up... well, can't type that here. But you get what I'm saying.
Thanks for the input, both mechanically and personally.
I'll let you know what I end up doing.

Aaron