Circuit/System Testing
IMPORTANT:
Circuit/System Verification must be performed first or misdiagnosis may result.
- Ignition OFF, disconnect the engine harness connector from the cooling fan speed control module.
- Ignition OFF, install a test lamp between the cooling fan speed control circuit terminal X3 49 and B+. The lamp should be OFF.
- If the lamp is ON, test the cooling fan speed control circuit for a short to ground. If the circuit tests normal, replace the ECM.
- Ignition ON, command the cooling fan ON with a scan tool. The lamp should be ON.
- If the lamp is OFF, test the cooling fan speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition OFF, disconnect the cooling fan harness connector at the cooling fan speed control module.
- Connect a jumper wire between the fan ground circuit terminal 1 and ground. Connect a 30A fused jumper wire between the positive terminal at the battery and the fan voltage supply circuit terminal 4 and verify fan activation.
- If the cooling fan does not activate, replace the cooling fan.
- Ignition OFF, measure between the cooling fan speed control module ground circuit terminal 2 at the harness connector and ground for less than 1 ohm.
- Install appropriately fused jumpers in the power and ground circuits between the cooling fan speed control module harness connector terminals and the cooling fan harness connector terminals. The fan should activate at full speed.
- If the fan does not activate correctly, test the cooling fan speed control module voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, replace the cooling fan speed control module.
- If the ECM, fan, and all circuits test normal, replace the cooling fan speed control module.