• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance |
---|---|---|---|---|---|
Cooling Fan Speed Control Circuit | P0480 | P0480 | P0480 | P0480 | -- |
The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is affected by many different conditions and can be adjusted from 10-90 percent duty cycle. Ninety percent is considered high fan speed. When multiple cooling speed requests are received, the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation, the control circuit voltage will be low and near battery voltage when the fan is OFF.
Engine running, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.
Important: The Circuit/System Verification must be performed first or misdiagnosis may result.
⇒ | 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. |
⇒ | If the lamp brightness does not change correctly, 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. |
⇒ | If greater than the specified range, repair the module ground circuit for open/high resistance. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
⇒ | If the cooling fan does not activate, replace the cooling fan. |
• | Control Module References for ECM replacement, setup, and programming |
Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.