#08-06-03-006A: Engine Running with Key Off, Continuous Run - Sensing and Diagnostic Module (SDM), No Communication, Service Air Bag Light Illuminated (Install Diode to Solenoid/Relay) - (Jan 29, 2009)
Subject: Engine Running with Key Off, Continuous Run -- Sensing Diagnostic Module (SDM), No Communication, Service Air Bag Light Illuminated (Install Diode to Solenoid/Relay)
Models: 2007-2009 Chevrolet Silverado 2500-3500 Series
2007-2009 GMC Sierra 2500-3500 Series
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This bulletin is being revised to update information and add a procedure. Please discard Corporate Bulletin Number 08-06-03-006 (Section 06 -- Engine/Propulsion System).
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Condition
Some customers may comment on the engine running for 10-15 seconds with the key off, and/or the supplemental inflatable restraint (SIR) MIL Lamp and Service Air Bag Message are illuminated.
Cause
These vehicles may be equipped with aftermarket equipment, i.e. a snow plow or a salt spreader system, that is controlled by a large solenoid or relay. When an electromechanical solenoid or relay is de-energized rapidly by a mechanical switch or semiconductor, the collapsing magnetic field produces a substantial transient voltage in its effort to disperse the stored energy and oppose the sudden change in current flow. These voltage spikes can occur at the positive terminal when the solenoid or relay is de-energized (keyed-off). If a solenoid or relay is wired onto the Run/Crank circuit of the vehicle to control aftermarket equipment, the spikes can be transmitted onto the circuit. The spikes can permanently damage the internal circuitry of the TCM and/or the SDM.
If the transmission control module (TCM) is damaged, it is possible for the TCM to pass retained accessory power onto the Run/Crank circuit keeping the engine control module (ECM) on until retained accessory power goes low.
If the sensing diagnostic module (SDM) is damaged, the SDM will not communicate, and it will illuminate the supplemental inflatable restraint (SIR) lamp and the Service Air Bag message.
Correction
Important: DO NOT replace the TCM or the SDM until the root cause of the condition has been identified to the solenoid/relay voltage spikes.
To prevent damage to any of the sensitive electronic components on the bussed circuit, the solenoid/relay MUST have the control circuit suppressed with a diode. The diode will prevent the voltage spikes from being transmitted onto the Run/Crank circuit.
Install a diode, P/N 12112422, across the coil of the solenoid. It is important that the striped end of the diode be connected to the positive terminal of the coil and the other end of the diode be connected to ground.
Important: Be sure to insulate the diode with heat shrink tubing before installing as shown in the picture above.
Notice: Some solenoids/relays may only have a positive post and will get their ground through their mounting bracket. In this case, the striped end of the diode is to be connected to the positive terminal and other end should be connected to the ground of the solenoid/relay.
Install a diode, P/N 12112422, across the coil of the relay. It is important that the striped end of the diode be connected to the positive terminal of the coil and the other end of the diode be connected to ground. Be sure to insulate the diode with heat shrink tubing before installing.
Parts Information
Part Number
Description
Qty
12112422
Diode
1
Warranty Information
This repair will not be covered under warranty due to the failure being caused by an aftermarket accessory.
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. See your GM dealer for information on whether your vehicle may benefit from the information.
