Cooling Fan Inoperative 3.8L (L26)
Diagnostic Instructions
Circuit/System Description
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the engine control module (ECM), or powertrain control module (PCM) to operate both
fans together at low or high speeds. The cooling fans receive positive voltage from the cooling fan relays which receive battery positive voltage from the underhood fuse block.
During low speed operation, the ECM or PCM supplies the ground path for the low speed fan relay, which is fan 1 relay, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts,
and supplies battery positive voltage from the fan 1 fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the series/parallel relay, which is fan 2 relay, and the
right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the ECM or PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The ECM or PCM grounds the high speed fan relay, which is fan 3 relay, and the series/parallel
relay through the high speed cooling fan relay control circuit. This energizes the series/parallel relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing
the relay contacts and provides battery positive voltage from the fan 2 fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is
a parallel circuit with both fans running at high speed.
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
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- If DTCs P0480 or P0481 are set, perform those diagnostics first.
- Verify with a scan tool that the ECM or PCM 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
- Ignition OFF, disconnect the series/parallel fan relay, which is fan 2 relay.
- 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 fan relays.
- Connect a 30A fused jumper between the normally-open switch contact terminals 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 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 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 and the fan voltage supply circuit terminal at the low speed fan relay and the high speed fan relay connection and verify the 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
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Repair Verification
Ignition ON, command the fan relay ON and OFF with a scan tool. Observe to verify that the appropriate fan turns ON and OFF with each command.
Cooling Fan Inoperative 3.6L LY7
Diagnostic Instructions
Circuit/System Description
The engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.
In low speed operation, the ECM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low relay. The left fan is connected in series
to the right cooling fan through the de-energized series/parallel fan 2 relay. The series circuit operates both fans at low speed.
In high speed operation, the ECM applies a ground to the coil side of the low speed fan 1 relay, the series/parallel fan 2 relay, and the high speed fan 3 relay. When energized, the high speed fan 3 relay applies voltage directly
to the right cooling fan through the switch side of the relay. Simultaneously, the low speed fan 1 relay and the series/parallel fan 2 relay provide ignition voltage and a direct path to ground for the left cooling fan. With both fans connected
in a parallel circuit, each fan receives full voltage and operates at high speed.
Reference Information
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling System 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, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fans turn ON and OFF when changing between the commanded states.
Circuit/System Testing
- Ignition OFF, disconnect the cooling fan relays.
- Connect a 30A fused jumper between the relay switch circuit terminal M15 and the ground circuit terminal K14 at the fan 2 relay connector. This will complete the left side fan ground circuit. Leave this jumper in place for the
remainder of this procedure.
Important: The following test must be performed on both the high speed fan 2 relay circuit and the low speed fan 1 relay circuit.
- Ignition ON, verify that a test lamp illuminates between ground and the relay switch B+ circuit terminal listed below:
| • | High speed fan 3 relay terminal K18 |
| • | Low speed fan 1 relay terminal A18 |
| ⇒ | If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output
circuit for a short to ground. If the circuit tests normal, test or replace the relay. |
Important: The following test must be performed first on the high speed fan 2 relay circuit and next on the low speed fan 1 relay circuit. Leave the jumper connected to the low speed fan 1 relay circuit for
the next test.
- Connect a 30A fused jumper between the relay switch B+ circuit and the relay controlled output circuit terminals listed below. Verify the appropriate fan is activated
| • | High speed fan 3 relay terminal K18 and terminal M19 |
| • | Low speed fan 1 relay terminal A18 and terminal C19 |
| ⇒ | If the appropriate fan does not activate, test the relay controlled output 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 circuit tests
normal, replace the fan. |
- Install the series/parallel fan 2 relay. Verify both fans activate at low speed.
| ⇒ | If both fans do not activate, test the relay controlled output circuit terminal L14 of the fan 2 relay for a short to ground or an open/high resistance. |
- If all circuits test normal, test or replace the relay.
Component Testing
- Ignition OFF, disconnect the cooling fan relay.
- Test for 70-110 ohms of resistance between terminals 85 and 86.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
- Test for infinite resistance between the following terminals:
| ⇒ | If not the specified range, replace the relay. |
- Test for less than 2 ohms of resistance between terminals 30 and 87A.
| ⇒ | If greater than the specified range, replace the relay. |
- Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Cooling Fan Inoperative w/LS4
Diagnostic Instructions
Circuit/System Description
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds.
The cooling fans receive positive voltage from the cooling fan relays which receive battery positive voltage from the underhood fuse block.
During low speed operation, the ECM supplies the ground path for the low speed fan relay, which is fan 1 relay, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and
supplies battery positive voltage from the fan 1 fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the series/parallel relay, which is fan 2 relay, and the right
cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The ECM grounds the high speed fan relay, which is fan 3 relay, and the series/parallel relay through
the high speed cooling fan relay control circuit. This energizes the series/parallel relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts
and provides battery positive voltage from the fan 2 fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit
with both fans running at high speed.
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
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- If DTCs P0480 or P0481 are set, 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
- Ignition OFF, disconnect the series/parallel fan relay, which is fan 2 relay.
- 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 fan relays.
- Connect 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 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 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 and the fan voltage supply circuit terminal at the low speed fan relay and the high speed fan relay connection and verify the 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
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Repair Verification
Ignition ON, command the fan relay ON and OFF with a scan tool. Observe to verify that the appropriate fan turns ON and OFF with each command.
