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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2005 Chevy: Silverado..cranks..wont glow plug voltage

Customer Question

2005 Chevy 3500 Silverado duramax cranks but won't start cold. No trouble codes stored, Modis troubleshooter recommended watching for rpm signal, sufficient at cranking speed. noticed no glow plug voltage when controller commanded on. replaced glow plug relay on advice of chevy dealer service advisor (fails commonly) vehicle started immediately and ran fine for a week. Customer reported no start same as before and commented that he had noticed that prior to the relay being replaced the glow plug indicator stayed lit for about 9 seconds and after our "fix" it was only on for an average of 3 seconds. We rescanned and had numerous injector driver codes (6 out of 8 cylinders) but once again had no voltage to glow plugs. Weather has been in single digits lately and unfortunately it seems to start fine here at the shop but when left at ski area overnight it will not start.
Submitted: 8 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 8 years ago.
WelcomeCustomer Do you have the exact codes?
Customer: replied 8 years ago.
Unfortunately we lost to post it we wrote them on. going to drive this afternoon and retest.
Expert:  GM Tech (Cam) replied 8 years ago.
Let me know when you get them.
Customer: replied 8 years ago.
Drove vehicle 30 miles and could not recreate dtc's. I am more interested in the glow plug system at this point. Did not start this morning at about 10 degrees. Glow plug lite stays on only 3 seconds. 48 k on odo for the record.
Expert:  GM Tech (Cam) replied 8 years ago.
Ok, HERE Is some information on the glow plug system. Have you tried boosting it cold to see if the cranking rpm is the issue?
GM Tech (Cam) and other Chevy Specialists are ready to help you
Customer: replied 8 years ago.

The first time the vehicle was towed in the glow plug controller was commanded on but there was no voltage to the plugs (on the scanner) After replacing the controller we had voltage. Now there is no voltage again. am I missing something? Did we burn up a controller by not addressing the cause of the original failure? Shorted glow plug, etc.

Expert:  GM Tech (Cam) replied 8 years ago.
Do you have power on the thick power wire into the GPCM?
Customer: replied 8 years ago.
Yes on the power wire, checked it again. Starts right up if you plug it in for an hour. Again specifically, is there another reason the controller would work (show voltage to the glow plugs on the scanner) for a short period of time (a week) and then fail in the same manner as the first. I can't help but feel we either misdiagnosed the first controller or missed the cause of its original failure.
Expert:  GM Tech (Cam) replied 8 years ago.
Have you checked all the glow plugs? Can you post the VIN?
Customer: replied 8 years ago.
1GBJK33265F836711, glow plug resistance is as follows front to rear right bank 1.2, 1.2, 1.1, 1.3 left bank 1.6, 1.1, 1.0, 0.8 pulled a couple for physical inspection.We subscribe to shop key and I requested more test and diagnostic info as there is next to nothing currently listed, ie glow plug resistance or GPCM testing of any sort. Two days later still waiting. The info you attached was a glow plug 101 overview, basics. I am still looking for specific test procedures and or input from someone familiar with this system along with some hands on cold weather experience. I'm accepting with this post but am no closer to a solution than before.
Expert:  GM Tech (Cam) replied 8 years ago.
The manual indicates that a resistance below 1 ohm is too low, replace the one that is low and see what happens.
Customer: replied 8 years ago.
Update, plugged in last nite and wouldn't start this morning, DTCU0106. Cannot find flow chart for htis DTC in Shopkey(again) btw checked the coolant temp with scanner and showed 105 after being plugged in, is this normal? Specific question, what should the voltage be at the glow plugs on the scanner when the controller is commanded on?
Expert:  GM Tech (Cam) replied 8 years ago.

With the engine coolant heater plugged in, the coolant will read that.

Below is some information on that code.

This is a crank no start?

PIT4090: SES MIL DTC U0100 U0101 U0105 and/or U0106 - keywords communication erratic low power shift - (Jul 27, 2006)

Subject:SES MIL DTC U0100 U0101 U0105 and/or U0106

Models:2004-2005 Chevrolet Silverado
2004-2005 GMC Sierra
with 6.6L RPO LLY engine


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


Some owners may comment of a SES MIL on and if DTCs are checked with the Tech 2 a U0100, U0101, U0105, and/or U0106 will be set. The ECM, TCM, FICM, and Glow Plug Controller communicate between each other on circuits 2361 and 2362 (CAN Buss), the Tech 2 does not communicate on these circuits.


In most cases, if all the DTCs set it could be caused by the Can Buss circuits shorted to ground. Cases for either of these circuits shorting to ground at the FICM/Alternator bracket have been reported. Before replacing any parts perform a thorough visual inspection of this wiring harness near the FICM/Alternator bracket and repair as necessary if shorted.



Glow Plug System Description

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the instant start system (ISS) glow plugs is accomplished by a glow control module unit and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the controller within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.

A normal functioning system operates as follows:

Turn the ignition ON with the engine OFF, and at room temperature.
The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.
The glow plug wait lamp is ON for 1 second during cold start.
The glow plug wait lamp may not illuminate during a warm engine start.
If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

The ECM provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

Glow Plugs

The glow plugs are 4.7 volt heaters in each of the cylinders that turn ON, then pulse-width modulated when the ignition switch is turned to the RUN position prior to starting the engine. They remain pulsing a short time after starting, then they are turned OFF.

A Wait to Start lamp on the instrument panel provides information on engine starting conditions. The Wait to Start lamp will not illuminate during post-start glow plug operation.

Glow Plug/Controller

The glow plug controller is a solid state device which operates the glow plugs. The glow plug controller is connected to the following circuits:

The fuel heater ignition 1 voltage circuit
The battery voltage circuit
The CAN communication circuit located between the engine control module (ECM) and the glow plug controller
The engine ground circuit
The glow plug supply voltage circuits located between the glow plug controller and the glow plugs.

The glow plug diagnostic circuits are directly monitored individually by using a separate transistor to control current to each glow plug. Individual diagnosis is thus possible for every glow plug.

Customer: replied 8 years ago.

So far it turns out to have been the edge power chip installed inline in the vehicle harness. Disconnected it and the vehicle starts and runs fine.

Expert:  GM Tech (Cam) replied 8 years ago.
That's good. The less that is wrong on the truck, the better.