Circuit/System Testing

WARNING: This page is about a different car, 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.

Ignition OFF, disconnect the ECM connector (X3).
Ignition ON, measure the voltage on the harness of the ECM connector (X3-66) for 5 V.
- If you have 5 V, test or replace the ECM.
- If the value is other than 5 V, test harness for:
  - Short to Voltage
  - Short to Ground
  - Open
If no trouble found, replace the TCM.