Cooling Fan Always On with V8
Diagnostic Instructions
| • | 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 the diagnostic category. |
Circuit/System Description
One Cooling Fan-3 Relays
The engine cooling fan system consists of one electrical cooling fan, two resistors, and three fan relays. The relays are arranged in a configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. These speeds are obtained by three separate circuits within the cooling fan. Each circuit contains a unique resistance value. The cooling fan and fan relays receive battery positive voltage from the underhood fuse block. The ECM controls the 3 relays by grounding the relay control circuit.
Two Cooling Fans-3 Relays
The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.
In low speed operation, the ECM applies ground to the coil side of the low speed relay, which is R1 cool/fan 1 relay. Voltage is applied directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay, which is R7 cool/fan 2 relay, so that both fans operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the low speed relay, the series/parallel relay, and the high speed relay, which is relay R2 cool/fan relay. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed relay and ground through the series/parallel relay.
When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage. If the ECM detects that the actual voltage of the relay control circuit is different than the expected voltage, DTC P0480 or P0481 will set and the affected ECM driver will be disabled.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Verify that DTCs P0480, P0481, P0691, P0692, P0693 and P0694 are not set.
- Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
- Ignition ON, observe that the fan is not activated.
| ⇒ | If any cooling system DTCs are set, repair the DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle. |
Circuit/System Testing
- Ignition OFF, disconnect each cooling fan relay, one at a time.
- Ignition ON, observe that the fan is not activated.
Important: The following tests must be performed on each relay.
| ⇒ | If the fan is activated, test for a short to voltage in the relay controlled output circuit. |
| ⇒ | If the fan is not activated, test or replace the appropriate cooling fan relay. |
Repair Verification
- Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
- Ignition ON, observe that the fan is not activated.
