Checking the Engine Cooling Fan

CHECKING THE ENGINE COOLING FAN





Preconditions
^ DTCs absent.
^ The fault is permanent.

Fault Sources
^ Constant half speed:
- Signal lead half speed short circuited to ground.
- Faulty Fan Control (FC) Relay.
^ Constant full speed:
- Signal lead full speed short circuited to ground.
- Faulty FC relay.
^ No half speed:
- Faulty FC relay or engine cooling fan.
^ No full speed:
- Break in signal lead full speed.
- Faulty FC relay or engine cooling fan.
^ Neither half speed nor full speed:
- Break in voltage supply or ground lead.
- Faulty FC relay or engine cooling fan.

TESTING PROCEDURE

Symptom
^ If the engine cooling fan operates at half speed the whole time even when the ignition is OFF:
- Proceed to: Checking the Fan Control Relay, Half Speed section below.

^ If the engine cooling fan operates at full speed the whole time even when the ignition is OFF:
- Proceed to: Checking the Fan Control Relay, Full Speed section below.

^ If neither of the above symptoms appears:
- Check the engine cooling fan.





Checking the Engine Cooling Fan
^ Use Diagnostic Test Mode 3 (DTM 3) to check if the engine cooling fan works at half speed and full speed.
^ See: System Diagnosis / Output Device Test - Diagnostic Test Mode 3.

If the engine cooling fan does work at both speeds:
- The fault is intermittent.
If the engine cooling fan only works at half speed:
- Check the signal lead, full speed.
If the engine cooling fan only works at full speed:
- Proceed to: Checking the Fan Motor, Half Speed Section below.
If the engine cooling fan does not work at all:
- Proceed to: Checking the Ground Lead section below.





Control Signal Lead, Full Speed
^ Connect the break-out box and check the ground connections.
^ Disconnect connector B from the FC relay.





^ Connect an ohmmeter between coupling B connector 2 and #22 (ECM A22) on the break-out box.

The ohmmeter should show approx. 0 Ohms.

If the reading is OK:
- Check the fan motor, full speed.
If the ohmmeter shows infinite resistance:
- Check the lead between FC relay connector B2 and ECM A22 for signs of a break.





Checking the Fan Motor, Full Speed
^ Ignition OFF.
^ Disconnect connector C from the FC relay.
^ Connect an ohmmeter between coupling C connector 2 and ground.

The ohmmeter should show 0 - 10 Ohms.

If the reading is OK:
- Test with a new FC relay.
If the reading is incorrect:
- Test with a new engine cooling fan.





Checking the Fan Motor, Half Speed Section
^ Ignition OFF.
^ Disconnect connector C from the engine cooling fan relay.
^ Connect an ohmmeter between coupling C connector 1 and ground.

The ohmmeter should show 0 - 10 Ohms.

If the reading is OK:
- Test with a new FC relay.
If the reading is incorrect:
- Test with a new engine cooling fan.





Checking the Ground Lead
^ Ignition OFF.
^ Disconnect the ground lead's single-pin connector (C/EA).
^ Connect an ohmmeter between the single-pin connector (on body) and ground.

The ohmmeter should show approx. 0 Ohms.

If the reading is OK:
- Check the fan motor.
If the reading is incorrect:
- Check the ground connector for signs of contact resistance and oxidation.
- Check also the lead between the fan motor and ground for signs of a break.





Checking the Fan Motor
^ Ignition OFF.
^ Connect the ground lead's single-pin connector.
^ Disconnect connector C from the FC relay.
^ Connect an ohmmeter between coupling C connector 2 and ground.

The ohmmeter should show 0 - 10 Ohms.

If the reading is OK:
- Test with a new FC relay.
If the reading is incorrect:
- Test with a new engine cooling fan.





Checking the Fan Control Relay, Half Speed
^ Ignition OFF.
^ Disconnect connector B from the FC relay.

If the engine cooling fan stops:
- Check the lead between FC relay connector B1 and ECM A7 for signs of short circuiting to ground.
If the engine cooling fan does not stop:
- Test with a new FC relay.





Checking the FC Relay, Full Speed
^ Ignition OFF.
^ Disconnect connector B from the FC relay.

If the engine cooling fan stops:
- Check the lead between FC relay connector B2 and ECM A22 for signs of short circuiting to ground.
If the engine cooling fan does not stop:
- Test with a new FC relay.