Inspection Procedure 4

INSPECTION PROCEDURE 4: Cooling Fan Does Not Change Speed or Does Not Stop

NOTE: If the engine coolant temperature reaches 110°C (230°F) or higher, the cooling fan control runs the cooling fan for up to 5 minutes even after the ignition switch is turned to the "LOCK" (OFF) position [the fan stops its rotation when the engine coolant temperature decreases to 110°C (230°F) or lower.]

Cooling Fan Drive Circuit:

CIRCUIT OPERATION
^ The fan control module is powered from fusible link number 2.
^ The 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 fan control module has variable control of the cooling fan motor speed using signals transmitted from the ECM.

TROUBLESHOOTING HINTS
^ Malfunction of fan control relay
^ Malfunction of fan control module
^ Malfunction of ECM

DIAGNOSIS

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

STEP 1. Check the fan control relay.
Q: Is the fan control relay in good condition?
YES: Go to Step 2.
NO: Replace the part, then go to Step 8.

STEP 2. Check the harness wire between fan control relay connector A-09X terminal 2 and fan control module connector A-17 terminal 3.








Q: Are the harness wire between fan control relay connector A-09X and fan control module connector A-17 damaged?
YES: Repair or replace the part, then go to Step 6.
NO: Go to Step 3.

STEP 3. 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. Measure the voltage between terminal number 18 and ground by backprobing.
^ The voltage should measure less than 0.3 volt when the cooling fan is not operating.
Q: Is the voltage less than 0.3 volt when the cooling fan is not operating?
YES: Go to Step 6.
NO: Go to Step 4.

STEP 4. 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 6.
NO: Go to Step 5.

STEP 5. 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 8.
NO: Go to Step 6.

STEP 6. Check the fan control module at ECM connector C-121.





1. Do not disconnect ECM connector C-121.
2. Pull out terminal number 21.
3. Turn the ignition switch to the "ON" position.
Q: Does the cooling fan motor operate?
YES: Replace the ECM. Then go to Step 8.
NO: Go to Step 7.

STEP 7. Check the fan control module at ECM connector C-121.





1. Disconnect ECM connector C-121.
2. Pull out terminal number 18.
3. Connect terminal number 18 to the body ground.
4. Turn the ignition switch to the "ON" position.
Q: Does the cooling fan motor stop running?
YES: Replace the ECM. Then go to Step 8.
NO: Replace the fan control module. Then go to Step 8.

STEP 8. Check the symptoms.
Q: Does the cooling fan operate correctly?
YES: The procedure is complete.
NO: Return to Step 1.