[Previous][Next]
Inspection Procedure 29: Fan Control Relay System
 
 
 
 
CIRCUIT OPERATION
  • The battery voltage is applied to the cooling fan control relay (low) coil and cooling fan control relay (high) coil from the ignition switch <Vehicles without KOS> or IG2 relay <Vehicles with KOS>.
  • The ECM connector terminal F/LO and F/HI turns on the switch of the power transistor on the unit, and then turns on the switch of the relay by applying the electrical current to the cooling fan control relay (low) coil or cooling fan control relay (high) coil.
  • When the cooling fan control relay (low) is in ON position, the battery voltage is applied to the cooling fan motor from the cooling fan control relay (low).
  • When the cooling fan control relay (low) and cooling fan control relay (high) are in ON position, the battery voltage is applied to the cooling fan motor from the cooling fan control relay (high).
 
 
COMMENT
  • When the cooling fan control relay (low) is in ON position, the fan motor rotates with the low speed.
  • When the cooling fan control relay (low) and the cooling fan control relay (high) are in ON position, the fan motor rotates with the high speed.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this case:)
  • Failed cooling fan control relay
  • Failed cooling fan motor
  • Open/short circuit in or damage to the cooling fan control relay circuit or loose connector contact
  • Failed ECM
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Check cooling fan control relay (low) and cooling fan control relay (high).
Check cooling fan control relay (Refer to GROUP 14 - On-vehicle Service - Fan Control Relay Continuity Check ).
Is the measured resistance normal?
Go to Step 2.
Replace cooling fan control relay.
 
STEP 2. Check cooling fan motor itself.
Check cooling fan motor (Refer to GROUP 14 - On-vehicle Service - Cooling Fan Motor Check ).
Is the fan motor operating properly?
Go to Step 3.
Replace fan motor.
 
STEP 3. Measure the voltage at cooling fan control relay (low) connector.
(1) Disconnect the connector and measure at relay box side.
(2) Measure the voltage between terminal battery line and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 4.
Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in power supply line between battery and cooling fan control relay (low) connector.
 
STEP 4. Perform voltage measurement at cooling fan control relay (low) connector.
(1) Disconnect the connector and measure at relay box side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal IG2 line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 5.
<Vehicles without KOS> : Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in IG2 line between ignition switch and cooling fan control relay (low) connector.
<Vehicles with KOS> : Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in IG2 line between IG2 relay and cooling fan control relay (low) connector.
 
STEP 5. Measure the voltage at cooling fan control relay (high) connector.
(1) Disconnect the connector and measure at relay box side.
(2) Measure the voltage between terminal battery line and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 6.
Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in power supply line between battery and cooling fan control relay (high) connector.
 
STEP 6. Measure the voltage at cooling fan control relay (high) connector.
(1) Disconnect the connector and measure at relay box side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal IG2 line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 7.
<Vehicles without KOS> : Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in IG2 line between ignition switch and cooling fan control relay (high) connector.
<Vehicles with KOS> : Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in IG2 line between IG2 relay and cooling fan control relay (high) connector.
 
STEP 7. Check of damage in power supply line between battery and cooling fan control relay (low) connector.
Is the harness wire in good condition?
Go to Step 8.
Repair the connector(s) or wiring harness.
 
STEP 8. Check of damage in power supply line between battery and cooling fan control relay (high) connector.
Is the harness wire in good condition?
Go to Step 9 <Vehicles without KOS>.
Go to Step 11 <Vehicles with KOS>.
Repair the connector(s) or wiring harness.
 
STEP 9. Check of damage in IG2 line between ignition switch connector and cooling fan control relay (low) connector.
Is the harness wire in good condition?
Go to Step 10.
Repair the connector(s) or wiring harness.
 
STEP 10. Check of damage in IG2 line between ignition switch connector and cooling fan control relay (high) connector
Is the harness wire in good condition?
Go to Step 11.
Repair the connector(s) or wiring harness.
 
STEP 11. Check of damage in IG2 line between IG2 relay connector and cooling fan control relay (low) connector.
Is the harness wire in good condition?
Go to Step 12.
Repair the connector(s) or wiring harness.
 
STEP 12. Check of damage in IG2 line between IG2 relay connector and cooling fan control relay (high) connector.
Is the harness wire in good condition?
Go to Step 13.
Repair the connector(s) or wiring harness.
 
STEP 13. Measure the voltage at ECM connector.
(1) Disconnect the connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal F/LO line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 14.
  • Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in F/LO line between cooling fan control relay (low) connector and ECM connector.
 
STEP 14. Perform voltage measurement at ECM connector.
(1) Disconnect the connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal F/HI line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 15.
  • Repair or replace the connector(s), or check and repair the harness of short circuit to ground, and open circuit in F/HI line between cooling fan control relay (high) connector and ECM connector.
 
STEP 15. Check of damage in F/LO line between cooling fan control relay (low) connector and ECM connector.
Is the harness wire in good condition?
Go to Step 16.
Repair the connector(s) or wiring harness.
 
STEP 16. Check of damage in F/HI line between cooling fan control relay (high) connector and ECM connector.
Is the harness wire in good condition?
Go to Step 17.
Repair the connector(s) or wiring harness.
 
STEP 17. Measure the resistance at cooling fan motor connector.
(1) Disconnect the connector and measure at the relay box side.
(2) Measure the resistance between terminal ground line and ground.
  • Continuity (2 ohms or less)
Does continuity exist?
Go to Step 18.
  • Check and repair harness between cooling fan motor connector and body ground. Repair or replace the connector, or check and repair the harness of damage in ground line between cooling fan motor connector and body ground.
 
STEP 18. Check of open circuit, short circuit, and damage in power supply line between cooling fan control relay (low) connector and cooling fan motor connector.
Is the harness wire in good condition?
Go to Step 19.
Repair the connector(s) or wiring harness.
 
STEP 19. Check of open circuit, short circuit, and damage in power supply line between cooling fan control relay (high) connector and cooling fan motor connector.
Is the harness wire in good condition?
Go to Step 20.
Repair the connector(s) or wiring harness.
 
STEP 20. Using scan tool (M.U.T.-III), check actuator test.
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Turn the ignition switch to the "ON" position.
(3) Set scan tool (M.U.T.-III) to the actuator test mode for item 12, Radiator fan relay (high).
  • Cooling fan motor rotates at high speed.
(4) Set scan tool (M.U.T.-III) to the actuator test mode for item 13, Radiator fan relay (low).
  • Cooling fan motor rotates at low speed.
(5) Turn the ignition switch to the "LOCK" (OFF) position.
Are the fan motors operating properly?
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
Replace ECM.