Sierra Classic 2500 4WD V8-6.0L (2007)
Diode: Customer Interest
Electrical - Engine Runs With Key OFF/Air bag Lamp ON
TECHNICAL
Bulletin No.: 08-06-03-006A
Date: January 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
Supercede:
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).
Condition
Some customers may comment on the engine running for 1015 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.
