multiple codes pulled????

[TRItech]

Hello to all,
I am a terminal tractor technician, and have been given the task of sorting out problems with one of our company vehicles, an 07 GMC 6.6L duramax, all factory conditions apply, save a K&N filter....
The following codes appear after they have been cleared beforehand:

p0672, p0673, p0674, p0675, p0677: Cylinder x glow plug circuit/open

p0726: Engine speed input circuit range/performance

p0727: No signal

To save a bit of conversation, I have taken the readings from the speed sensors, and they check out OK and within range. Also traced the corresponding wires back to the ECU, and found the same readings; no broken wires.

Had also a p0403 (exhaust gas recirculation control circuit) and a p0299 (turbo underboost) code, and replaced the motor on the EGR, and no longer have those codes at this time.

I have triple checked all connections (none unplugged, loose, or damaged), grounds (cleaned), power cables (cleaned).

I am about ready to have this truck taken over to a dealership, as I do not claim to be a duramax technician, but do know my way around a shop in large.

Any advice would be much appreciated; it seems you guys are well educated.

THANKS!

 

[JoshH]

What is the truck doing or not doing?

 

[Harbin_22]

All your glow plug codes are from bad glow plugs. Pretty common problem. Replace the ones that are bad or just do them all since you have so many bad. The rest won't be far behind.

Does the truck run correctly with the P0726 and P0727?