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Discussion Starter #1
I took my truck into the dealer for service because my wait to start light was staying on and i would just have to start the truck with the light on and then it would go out. The truck runs great, even cold. The dealer said the glow plugs are all testing fine, he said GM sent out a bulletin saying not to replace the glow plugs that it was a voltage issue in a control module for the glow plugs. This was just a preliminary bulletin so he has to call GM this week and see exactly what they want done, but i figured Id put it out there cause i know there are alot of guys on here that might be of help
 

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No check engine light?
 

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Diesel Engine Glow Plug Trouble Codes - keywords DTC GPCM hard P0671 P0672 P0673 P0674 P0675 P0676 P0677 P0678 SES start #PIP3586A - (Dec 16, 2005)
Diesel Engine Glow Plug Trouble Codes
2006 Chevrolet Express, Kodiak, Silverado

2006 GMC Savanna, Sierra, TopKick

Equipped with the 6.6 LBZ or LLY Duramax Diesel Engine

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A vehicle may be brought into the dealer with the SES light on and multiple cylinder glow plug DTCs set. Multiple glow plug DTCs may be caused by internal opens in the glow plugs. There are two different descriptions for an internal open in a glow plug. A fast open glow plug is a plug with an internal open circuitry, but no visual damage to the tip of the plug. A slow open glow plug is a plug that has internal open circuitry, and the tip of the plug is missing or damaged.

Recommendation/Instructions:
Complete current SI diagnostics for any DTCs found.

At this time engineering is involved with glow plug concerns and is requesting the steps below be completed if a glow plug concern is verified.

A loose connection on the Glow Plug Control Module (GPCM) ground, or the battery power feed cable may induce glow plug concerns. When the GPCM ground or battery feed circuit has a poor connection, the GPCM will sense a voltage fluctuation, and possibly induce the GPCM to power up the glow plugs. Untimed GPCM cycling may cause glow plug concerns.
Both ends of the battery feed cable to the GPCM and the GPCM ground must be inspected for a clean and tight connection. Connector C1 terminal 1 at the GPCM is a quick disconnect type of connector. Make sure terminal fit is clean and tight and the quick disconnect is seated properly. The source or main power feed location differs depending on the vehicle being serviced. On GMT800 C/K model trucks, the power feed stud is located in the Under Hood Bussed Electrical Center (UBEC). To access this power feed stud, the secondary UBEC cover has to be removed. On GMT610 "G" vans inspect the underhood junction block connection. On GMT560 4500/5500 trucks inspect the secondary fuse block connection. If a poor connection is found, and any of the glow plugs have an internal open circuit, all 8 glow plugs will need to be replaced. If a slow open glow plug (missing glow plug tip) is found, the cylinder head must be removed and all debris be cleaned out of the cylinder. If a fast open glow plug (no missing tip) is found all 8 glow plugs will need to be replaced, but the cylinder heads do not need to be removed.
There are other electrical scenarios that can induce glow plug concerns. If the glow plug system senses a certain electrical "noise" on the power feed (jump starting, batteries are disconnected then reconnected with the ignition ON, or a battery charger is used during a module reprogramming event) the glow plugs may also go open. If any of the glow plugs have an internal open circuit, all 8 glow plugs will need to be replaced. If a slow open glow plug (missing glow plug tip) is found, the cylinder head must be removed, and the debris be cleaned out of the cylinder. If a fast open glow plug (no missing tip) is found all 8 glow plugs will need to be replaced, but the cylinder heads do not need to be removed.
At this time do not replace the GPCM for all 8 internal opened glow plugs. GPCMs have been returned and inspected with no problem found.
This PI will be updated when more information becomes available.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
 

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Did they just give you that or did they try the suggested fixes?

Do you have a check engine light? If not, this doesn't really seem to apply to you.
 

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Test drove my new LBZ Today, came in a couple weeks early. :D Anyway, noticed that the glow plug light NOT coming on before I started it. I think the engine had been run and was already warm. Is this normal? Im new to diesels but i thought the light would come on anyway. So I had the truck overnight, and the next morning the light did come on for about 2 secs. Sat it at work for about 2 hours and came out to start it, no light again. Temps are about 15-20F, the trucks starts just fine and runs fantastic.;) Anything I should do before taking delivery?

-concerned about this glow plug issue, I dont want the heads being pulled after just couple hundred miles.
 

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It will normally only come on after a long cold night or for longer than 8 hours I have noticed. If the engine still has minimal heat in it they still don't seem to come on.
 

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Ditto... they DO come on, but it is okay to start immediately.
Part of the difference is on the '06, the injectors now spray onto the plugs.

If you watch your battery voltage, you'll be able to tell when the glow plugs and/or grid heater are running.
 

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Discussion Starter #10
Max, thanks for all the info. It sounds like my issue is in the power connection with the module. When I initially took the truck in, the tech said he looked at all the plugs through the scan tool and they were operating normal. he did mention some kind of issue with the module but would not replace anything until he called GM. called him today and he is still waiting for a call back. and yes the engine light is on, which pisses me off the most! truck runs great
 

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Discussion Starter #11
LBZFAN dont sweat it, the plugs will only come on for 2-4 seconds on the coldest days, and not at all if theres a little bit of heat in the motor. sounds like your all set. My issue was the plugs werent shutting off, the light would stay on constant until the motor was started
 
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