Inspection Procedure 3

INSPECTION PROCEDURE 3: Cooling Fan Does Not Operate

Cooling Fan Drive Circuit:

CIRCUIT OPERATION
^ The fan control module is powered from fusible link number 2.
^ The engine control module (ECM) judges the required revolution speed of cooling fan motor using the input signals transmitted from A/C switch, vehicle speed sensor and engine coolant temperature sensor. The ECM activates the fan control module to drive the cooling fan motor.

TECHNICAL DESCRIPTION
^ The cause could be a malfunction of the fan control module power supply or ground circuit.
^ The cause could also be a malfunction of the fan control module or the ECM.

TROUBLESHOOTING HINTS
^ Malfunction of fusible link
^ Malfunction of fan control relay
^ Malfunction of cooling fan motor
^ Malfunction of fan control module
^ Malfunction of ECM
^ Damaged wiring harness or connector

DIAGNOSIS

Required Special Tools:
^ MB991223: Harness Set
^ MB992006: Extra Fine Probe

STEP 1. Check the circuit at fan control module connector A-17 terminal 3.








1. Disconnect fan control module connector A-17, and measure at the harness side connector.
2. Measure the voltage between terminal number 3 and ground.
^ When the ignition switch is turned to the "ON" position, voltage should measure battery positive voltage.
Q: Is the voltage battery positive voltage when the ignition switch is turned to the "ON" position?
YES: Go to Step 7.
NO: Go to Step 2.

STEP 2. Check the fan control relay.
Q: Is the fan control relay in good condition?
YES: Go to Step 3.
NO: Replace it, then go to Step 1.

STEP 3. Check for harness damage between fusible link number 2 and fan control relay connector A-09X terminal 4.





Q: Are the harness wires between fusible link number 2 and fan control relay connector A-09X damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 4.

STEP 4. Check for harness damage between fan control relay connector A-09X terminal 2 and fan control module connector A-17 terminal 3.








Q: Are the harness wires between fan control relay connector A-09X terminal 2 and fan control module connector A-17 terminal 3 damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 5.

STEP 5. Check for harness damage between joint connector (6) C-105 and fan control relay connector A-09X.








NOTE: After inspecting intermediate connector A-13 terminal 3 and joint connector (6) C-105 terminal 28, 33 inspect the wires. If intermediate connector A-13 and joint connector (6) C-105 are damaged, repair or replace them.








Q: Are the harness wires between joint connector (6) C-105 terminal 28 and fan control relay connector A-09X terminal 1 damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 6.

STEP 6. Check for harness damage between fan control relay connector A-09X terminal 3 and ground.





Q: Are the harness wires between fan control relay connector A-09X terminal 3 and ground damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 7.

STEP 7. Check the cooling fan motor.
Q: Is the cooling fan motor in good condition?
YES: Go to Step 8.
NO: Replace it, then go to Step 13.

STEP 8. Check the circuit at fan control module connector A-17 terminal 1.








1. Disconnect fan control module connector A-17, and measure at the harness side connector.
2. Measure the resistance between terminal number 1 and ground.
^ The resistance should measure less than 2 ohms.
Q: Is the resistance less than 2 ohms?
YES: Go to Step 10.
NO: Go to Step 9.

STEP 9. Check the harness wire between fan control module connector A-17 and ground.





Q: Are the harness wires between fan control module connector A-17 and ground damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 10.

Step 10. Measure the output circuit voltage at ECM connector C-121 terminal 18 by backprobing.








1. Do not disconnect ECM connector C-121.
2. Start the engine and allow it to idle.
3. Turn the A/C switch to the "ON" position.
4. Measure the voltage between terminal number 18 and ground by backprobing.
^ The voltage should measure 0.7 volt or more when the cooling fan is operating.
Q: Is the voltage 0.7 volt or more when the cooling fan is operating?
YES: Go to Step 12.
NO: Go to Step 11.

Step 11. Check the harness wire between ECM connector C-121 and fan control module connector A-17.





NOTE: If intermediate connector A-13 terminal 2 is damaged, repair or replace it.








Q: Are the harness wires between ECM connector C-121 terminal 18 and fan control module connector A-17 terminal 2 damaged?
YES: Repair or replace them, then go to Step 13.
NO: Go to Step 12.

Step 12. Check the fan control module at ECM connector C-121.





1. Do not disconnect ECM connector C-121.
2. Pull out terminal number 18.
3. Turn the ignition switch to the "ON" position.
Q: Does the cooling fan motor operate?
YES: Replace the ECM. Then go to Step 13.
NO: Replace the fan control module. Then go to Step 13.

Step 13. Check the symptoms.
Q: Does the cooling fan operate correctly?
YES: The procedure is complete.
NO: Return to Step 1.