Checking the Engine Cooling Fan

FAULT TRACING INFORMATION

Preconditions
^ DTCs absent.
^ Fault permanent.

Symptoms
^ Engine coolant fan not running.
^ Engine coolant fan not running at low speed.
^ Engine coolant fan not running at full speed.
^ Engine coolant fan running constantly at low speed.
^ Engine coolant fan running constantly at full speed.

Fault Sources
^ Constant low speed:
- Low speed signal lead short circuited to ground.
- Defective engine coolant fan relay.
- Defective low speed pressure switch.
^ Constant full speed:
- Full speed signal lead short circuited to ground.
- Defective engine coolant fan relay.
- Defective full speed pressure switch.
^ No low speed:
- Low speed signal lead short circuited to live.
- Break in low speed signal lead.
- Defective engine coolant fan relay or engine coolant fan.
^ No full speed:
- Full speed signal lead short circuited to live.
- Break in signal lead.
- Defective engine coolant fan relay or engine coolant fan.
^ Neither low speed nor full speed:
- Break in power lead.
- Defective engine coolant fan relay or engine coolant fan.

TESTING PROCEDURE

Symptoms

If engine coolant fan runs constantly at low speed when ignition OFF:
- Proceed to: Check Low Speed Pressure Switch, section below.
If engine coolant fan runs constantly at full speed when ignition OFF:
- Proceed to: Check Full Speed Pressure Switch, section below.
If none of above symptoms occurs.
- Proceed to: Check Engine Coolant Fan Function, section below.





Check Engine Coolant Fan Function
^ Check using Diagnostic Test Mode 3 if engine coolant fan operates at low speed or full speed.

If engine coolant fan only runs at low speed:
- Proceed to: Check Signal Lead Resistance, Full Speed, section below.
If engine coolant fan only runs at full speed:
- Proceed to: Check Signal Lead Resistance, Low Speed, section below.
If engine coolant fan does not run at all:
- Proceed to: Check Main Fuse, section below.





Check Low Speed Pressure Switch
^ Ignition OFF.
^ Disconnect low speed pressure switch connector, J2 or L2 respectively.

Engine coolant fan should stop.

If engine coolant fan stops:
- Test with a new pressure switch.
If engine coolant fan does not stop:
- Proceed to: Check Engine Coolant Fan Relay, Low Speed, section below.





Check Engine Coolant Fan Relay, Low Speed
^ Ignition OFF.
^ Connect low speed pressure switch connector.
^ Disconnect engine coolant fan connector B.

Engine coolant fan should stop.

If engine coolant fan stops:
- Check lead between engine coolant fan relay contact B1 and ECM 14 for short circuit to ground.
If engine coolant fan does not stop:
- Test with a new engine coolant fan relay.





Check Full Speed Pressure Switch
^ Ignition OFF.
^ Disconnect full speed pressure switch connector, J3 or L3 respectively.

Engine coolant fan should stop.

If engine coolant fan stops:
- Test with a new pressure switch.
If engine coolant fan does not stop:
- Proceed to: Check Engine Coolant Fan Relay, Full Speed, section below.





Check Engine Coolant Fan Relay, Full Speed
^ Ignition OFF.
^ Connect full speed pressure switch connector.
^ Disconnect engine coolant fan relay connector B.

Engine coolant fan should stop.

If engine coolant fan stops:
- Check lead between engine coolant fan relay contact B2 and ECM 34 for short circuit to ground.
If engine coolant fan does not stop:
- Test with a new engine coolant fan relay.





Check Signal Lead Resistance, Full Speed
^ Ignition OFF.
^ Connect breakout box and check control points.
^ Disconnect engine coolant fan relay connector B.
^ Connect an ohmmeter between engine coolant fan relay connector B contact 2 and #34 on breakout box.

Ohmmeter should read approx. 0 ohms.

If value OK:
- Proceed to: Check Signal Lead, Full Speed, section below.
If value differs:
- Check lead between engine coolant fan relay contact B2 and ECM 34 for break.





Check Signal Lead, Full Speed
^ Engine coolant fan relay connector B disconnected.
^ Ignition ON.
^ Connect a voltmeter between engine coolant fan relay connector B contact 2 and ground.

Voltmeter should read approx. 0 Volts.

If value OK:
- Proceed to: Check Fan Motor, Full Speed, section below.
If value differs:
- Check lead between engine coolant fan relay contact B2 and ECM 34 for short circuit to live.





Check Fan Motor, Full Speed
^ Ignition OFF.
^ Disconnect engine coolant fan relay connector C.
^ Connect an ohmmeter between engine coolant fan relay connector C contact 2 and ground.

Ohmmeter should read 0 - 10 ohms.

If value OK:
- Test with a new engine coolant fan relay.
If value differs:
- Test with a new engine coolant fan.





Check Signal Lead Resistance, Low Speed
^ Ignition OFF.
^ Connect breakout box and check control points.
^ Disconnect engine coolant fan relay connector B.
^ Connect an ohmmeter between engine coolant fan connector B contact 1 and #14 on breakout box.

Ohmmeter should read approx. 0 ohms.

If value OK:
- Proceed to: Check Signal Lead, Low Speed, section below.
If value differs:
- Check lead between engine coolant fan relay contact B1 and ECM 14 for break.





Check Signal Lead, Low Speed
^ Engine coolant fan relay connector B disconnected.
^ Ignition ON.
^ Connect a voltmeter between engine coolant fan relay connector B contact 1 and ground.

Voltmeter should read 0 Volts.

If value OK:
- Proceed to: Check Fan Motor, Low Speed, section below.
If value differs:
- Check lead between engine coolant fan relay contact B1 and ECM 14 for short circuit to live.





Check Fan Motor, Low Speed
^ Ignition OFF.
^ Disconnect engine coolant fan relay connector C.
^ Connect an ohmmeter between engine coolant fan relay connector C contact 1 and ground.

Ohmmeter should read 0 - 10 ohms.

If value OK:
- Test with a new engine coolant fan relay.
If value differs:
- Test with a new engine coolant fan.





Check Main Fuse
^ Check if main fuse 7 (11A/7) in main fuse box behind battery is OK.

If fuse OK:
- Proceed to: Check Voltage to Relay, section below.
If fuse not OK:
- Check lead between main fuse 7 and engine coolant fan relay contact A1 for short circuit to ground.





Check Voltage to Relay
^ Ignition OFF.
^ Disconnect engine coolant fan relay connector A.
^ Ignition ON.
^ Connect a voltmeter between connector A and ground.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check Fan Motor, section below.
If value differs:
- Check lead between battery and engine coolant fan relay contact A1 for break.





Check Fan Motor
^ Ignition OFF.
^ Disconnect engine coolant fan relay connector C.
^ Connect an ohmmeter between engine coolant fan connector C contact 2 and ground.

Ohmmeter should read 0 - 10 ohms.

If value OK:
- Test with a new engine coolant fan relay.
If value differs:
- Check fan ground contact.
If ground contact OK:
- Test with a new engine coolant fan.