Circuit/System Testing
WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the X1 harness connector at the ECM.
- Connect a test lamp between the appropriate signal circuit terminal listed below and ground:
- Terminal 57 - with LV1
- Terminal 23 - with LWN
- Terminal 33 - with L96/LC8
- Ignition ON, turn the stop lamps ON and OFF by applying and releasing the brake pedal. The test lamp should turn ON and OFF when changing between the selected states.
- If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
- If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
- If all circuits test normal, replace the ECM.