Circuit/System Testing
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Turn OFF the ignition before inserting fingers into the throttle bore. Unexpected movement of the throttle blade could cause personal injury.
- Inspect the throttle body for the following conditions:
- A throttle blade that is NOT in the rest position
- A throttle valve that is binding open or closed
- A throttle blade that is free to move open or closed WITHOUT spring pressure
- If a condition is found, replace the throttle body assembly.
- Ignition OFF, disconnect the harness connector at the throttle body.
- Ignition ON, verify that a test lamp does not illuminate between motor control 1 circuit terminal B and ground.
- If test lamp illuminates, test the motor control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Ignition ON, verify that a test lamp does not illuminate between motor control 2 circuit terminal A and ground.
- If the test lamp illuminates, test the motor control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Ignition ON, verify that a test lamp does not illuminate between motor control 1 circuit terminal B and B+.
- If the test lamp illuminates, test the motor control circuit for a short to ground. If the circuit tests normal, replace the ECM.
- Ignition ON, verify that a test lamp does not illuminate between motor control 2 circuit terminal A and B+.
- If the test lamp illuminates, test the motor control circuit for a short to ground. If the circuit tests normal, replace the ECM.
- Ignition OFF, allow sufficient time for the ECM to completely power down. Connect a DMM between the motor control 1 circuit terminal B and ground.
- Measure for B+ on the motor control 1 circuit terminal B as the ignition is turned ON.
- If the peak voltage is not within 1 volt of B+, test the circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition OFF, allow sufficient time for the ECM to completely power down.
- Measure for B+ on the motor control 2 circuit terminal A as the ignition is turned ON.
- If the peak voltage is not within 1 volt of B+, test the circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- If all circuits test normal, replace the throttle body.
IMPORTANT:
Disconnecting the throttle body harness connector causes additional DTCs to set.
IMPORTANT:
When measuring peak voltage, ensure that the DMM is on the proper voltage scale and that the response time is set to 1 ms.