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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1386 (Transfer Case - Mp 1222/1225/1226-NQG) >> Diagnostic Information and Procedures >> Four-Wheel Drive Does Not Engage >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check the axle switch signal circuit for an open or high resistance.
    • If everything checks normal then go to the next step.
  2. Check the front axle actuator control circuit for an open or high resistance with the front axle actuator disconnected and the mode selection switch disconnected.
    • If everything checks normal reconnect the mode selection switch and retest. If the circuit still shows an open or high resistance then replace the switch. If the circuit indicates no open or high resistance then refer to Front Axle Actuator and Axle Testing .
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