• | 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 | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Low Speed Cooling Fan Relay Control Circuit | P0480 | P0480 | P0480 | -- |
Low Speed Cooling Fan Relay Coil Voltage Supply Circuit | P0480 | P0480 | P0480 | -- |
High Speed Cooling Fan Relay Control Circuit | P0481 | P0481 | P0481 | -- |
High Speed Cooling Fan Relay Coil Voltage Supply Circuit | P0481 | P0481 | P0481 | -- |
The engine control module (ECM) grounds the low speed relay, which is relay 1, and the high speed relay, which is relay 2, control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON, the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the ECM detects that the actual state of the control circuit does not match the expected state, a DTC will set.
• | The ignition is ON. |
• | The system voltage is between 8-18 volts. |
• | The engine speed is more than 40 RPM. |
• | The ECM driver transitions from ON to OFF or from OFF to ON. |
• | An improper voltage level has been detected on the cooling fan relay control circuit. |
• | The condition must be present for a minimum of 30 seconds. |
• | DTC P0480 is a Type B DTC. |
• | DTC P0481 is a Type B DTC. |
• | DTC P0480 is a Type B DTC. |
• | DTC P0481 is a Type B DTC. |
Cooling Fan Description and Operation
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Ignition ON, command each relay ON and OFF with a scan tool. Feel or listen to verify that each relay turns ON and OFF with each command.
⇒ | If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | If the fan does not activate, test the fan voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the fan. |
⇒ | If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and it's fuse is open, replace the relay. |
⇒ | If the test lamp does not illuminate, test the relay coil 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 relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.