Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2009AVALANCHE 6.0 Y, RWDREPAIR AND DIAGNOSISTRANSMISSIONAUTOMATIC TRANSAUTOMATIC TRANSMISSION - 6L80/6L90 - DTC P0218 TO DTC P0963DTC P071ACIRCUIT/SYSTEM TESTING
2009 Chevrolet Avalanche 6.0 Y, RWD
Circuit/System Testing
2009 Chevrolet Avalanche 6.0 Y, RWDSECTION Circuit/System Testing
- Ignition Off, transmission in Park, disconnect the Tow/Haul switch connector.
- Test for less than 1 ohm of resistance between the Tow/Haul switch signal circuit terminal B and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition On, verify the scan tool Tow/Haul parameter displays Inactive.
- If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.
- Install a fused jumper between the signal circuit and ground. Verify the scan tool parameter displays Active.
- If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
- If all circuits test normal, replace the Tow/Haul switch.
- If the electrical circuit checks are OK and the tow/haul shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents tow/haul operation. Refer to Symptoms - Automatic Transmission .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.