Cooling Fan Inoperative Except LAT
Diagnostic Instructions
Circuit/System Description
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 fan speed relay, which is the auxiliary fan relay 12. 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 fan control relay 15, so that both fans operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the low fan speed relay, the series/parallel relay, and the high speed fan relay, which is the main fan relay 16. Voltage is applied directly to the right cooling fan through
the switch side of the high speed fan relay. The left cooling fan obtains voltage through the low speed fan 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.
Reference Information
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References
for scan tool information
Circuit/System Verification
- If DTCs P0480 or P0481 are set, then perform those diagnostics first.
- Verify with a scan tool that the ECM is not commanding fan relay activation.
- Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that the fan turns ON and OFF with each command.
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Ignition OFF, disconnect the series/parallel relay, which is fan control relay 15.
- Ignition ON, activate the cooling fan relay 1 with a scan tool. The fan should be OFF.
| ⇒ | If the fan is activated, test the left fan ground circuit for a short to ground. |
- Ignition OFF, disconnect the remaining relays.
- Install a 30A fused jumper between the normally-open switch contact terminals 30 and 87 at the series/parallel relay connector in order to complete the fan ground circuit. Leave this jumper in place for the remainder of this procedure.
- One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal 87 at the low speed fan relay and the high speed fan relay connections and verify fan activation.
| ⇒ | If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuits test normal,
replace the fan. |
- Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 at the low speed fan, which is AUX fan relay 12, and the high speed fan
relay, which is main fan relay 16, connections and verify fan activation.
| ⇒ | 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 its fuse is open, test all connected components and replace as necessary. |
- If the circuits and fans test normal, replace the relay.
Repair Instructions
Repair Verification
Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that the fans turn ON and OFF with each command.
Cooling Fan Inoperative LAT
Diagnostic Instructions
Circuit/System Description
The engine control module (ECM) grounds the low speed relay, which is the AUX fan relay, and the high speed relay, which is the main fan relay, 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.
Reference Information
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References
for scan tool information
Circuit/System Verification
- If DTCs P0480 or P0481 are set, then perform those diagnostics first.
- Ignition ON, verify with a scan tool that the ECM is not commanding fan relay activation.
- Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that the fan turns ON and OFF with each command.
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Ignition OFF, disconnect the affected relay.
- Connect a 30A fused jumper wire between the positive voltage terminal at the battery and the fan voltage supply circuit terminal 87 and verify fan activation.
| ⇒ | 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, test the fan ground circuit for an open/high resistance. If the fan did not activate and the circuits
test normal, replace the fan. |
- Ignition ON, connect a 30A fused jumper wire between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 and verify fan activation.
| ⇒ | 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 its fuse is open, test all connected components and replace, as necessary. |
- If the fan and all circuits test normal, replace the relay.
Repair Instructions
Repair Verification
Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that each fan turns ON and OFF with each command.
Cooling Fan Inoperative LAT
Diagnostic Instructions
Circuit/System Description
The engine control module (ECM) grounds the fan main relay and the fan main relay 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.
Reference Information
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
Circuit/System Verification
- If DTCs P0480 or P0481 are set, perform those diagnostics first.
- Verify cooling fan operation using the scan tool commands listed below:
| • | Fan Relay 1 ON and Fan Relay 2 OFF--Fan runs at high speed. |
| • | Fan Relay 1 OFF and Fan Relay 2 ON--Fan runs at low speed. |
Circuit/System Testing
Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Ignition OFF, disconnect the relays.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground at each relay connector.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test the control circuit terminal 87 for a short to ground. |
- One at a time, connect a 30A fused jumper between terminal 30 and terminal 87 at each relay connection and verify fan activation.
| ⇒ | If the fan does not activate, test the control circuit terminal for an open/high resistance. If the circuit tests normal, test the fan ground circuit terminal 1 for an open/high resistance. If the circuits test normal, replace the fan. |
- If the circuits and fans test normal, replace the relay.
Repair Instructions
Cooling Fan and Shroud Replacement
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.
Cooling Fan Inoperative LE5
Diagnostic Instructions
Circuit/System Description
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 fan relay. Voltage is applied directly to the left cooling fan through the switch side of fan AUX relay 3. The right fan is connected in series to the left fan through the de-energized
FAN CTRL relay so that both fans operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of fan AUX relay, FAN CTRL relay, and fan main relay. Voltage is applied directly to the right cooling fan through the switch side of fan main relay. The left cooling fan obtains voltage
through fan AUX relay and ground through FAN CTRL relay 2.
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.
Reference Information
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
Circuit/System Verification
- Verify that the following DTCs are not set: P0480 or P0481.
| ⇒ | If any of the DTCs are set, repair the DTC first. |
- Verify cooling fan operation using the scan tool commands listed below:
| • | Fan Relay 3 ON--Both fans run at low speed. |
| • | Fan Relays 1 and 2 ON--The main fan runs at high speed, the AUX fan is OFF. |
| • | Fan Relays 1, 2, and 3 ON--Both fans run at high speed. |
Circuit/System Testing
Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Ignition OFF, disconnect FAN CTRL relay.
- Ignition ON, activate the fan relay 1 with a scan tool. The fan should be OFF.
| ⇒ | If the fan is activated, test the left fan ground circuit terminal 1 for a short to ground. |
- Ignition OFF, disconnect the remaining fan relays.
- Connect a 30A fused jumper between the normally-open switch contact terminals 30 and 87 at FAN CTRL relay connector in order to complete the left fan ground circuit. Leave this jumper in place for the remainder of this procedure.
- One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal 87 at each relay connection listed below and verify the appropriate fan activation:
| ⇒ | If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance. If the circuit tests normal, test the fan ground circuit for open/high resistance. If the circuits test normal, replace the
fan. |
- Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 at fan relay connections listed below and verify the appropriate fan activation:
| ⇒ | If the appropriate fan does not activate, test the relay switch voltage supply circuit for a short to ground or high resistance. |
- If the circuits and fans test normal, replace the relay.
Repair Instructions
Cooling Fan and Shroud Replacement
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.
