Important Information - PIP 3893A

#PIP3893A: Intermittent Engine Misfire And SES Light Due To Loss Of Voltage To Ignition Coils - keywords connector miss P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 P0351 P0352 P0353 P0354 P0355 P0356 - (Dec 3, 2008)

Subject: Intermittent Engine Misfire and SES Light due to Loss of Voltage to Ignition Coils

Models: 2005-2006 Cadillac Escalade
2005-2006 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe
2005-2006 GMC Savana, Sierra, Yukon
Equipped with a 4.8L, 5.3L, or 6.0L V8 Engine
(RPO Codes LR4, LM7, LQ4, or LQ9)

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

Condition/Concern:
On rare occasions, a customer may complain of a misfire and SES light. Upon inspection, no spark from the ignition coils may be observed and any of the following DTCs may be stored: P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0351, P0352, P0353, P0354, P0355, P0356, P0357, and/or P0358.

Recommendation/Instructions:
If the diagnosis does not isolate a cause for this concern, wiggle test the ignition coil harnesses to see if the concern can be duplicated. If so, the following areas could be causing an intermittent loss of ignition 1 voltage to the ignition coils and should be inspected:

- For C/K Trucks and Utilities, inspect S160, S159, C148, and C149 for poor connections. Also, inspect the circuits on both sides of C148 and C149 to see if any are broken inside of the insulation, especially the pink ignition 1 power feed circuit.

- For G Vans, inspect S184, S185, C126, and C127 for poor connections. Also, inspect the circuits on both sides of C126 and C127 to see if any are broken inside of the insulation, especially the pink ignition 1 power feed circuit.

If a concern is found with any of these areas, it should be repaired by following the repair procedures.

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.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.