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 MANUALSGMC2010SAVANA G2500, VAN CARGO EXTENDED, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1506 (AUTOMATIC TRANSMISSION - 2ML70 - DTC P0218 TO DTC P0965-P0967)DTC P077BCIRCUIT/SYSTEM TESTING
2010 GMC Savana G2500, Van Cargo Extended, 6.6 6
Circuit/System Testing
2010 GMC Savana G2500, Van Cargo Extended, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the harness connector at the sensor.
- Ignition ON, test for 8.3-9.3 V between the 8.5 V reference circuit terminal B and ground.
- If less than the specified range, test the 8.5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the Q8 control solenoid valve assembly.
- If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the Q8 control solenoid valve assembly.
- Disconnect the OSS connector.
- Test for 8.3-9.3 V between the OSS supply voltage circuit and ground.
- If less than 8.3 V, test the OSS supply voltage circuit for an open/high resistance or short to ground.
- If greater than 9.3 V, test the OSS supply voltage circuit for a short to voltage.
- Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test .
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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.