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DTC P1491: Radiator Fan Control Relay Circuit

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: Radiator fan control relay may also be referred to as radiator fan relay. Radiator fan control relay circuit is monitored when ignition is on, battery voltage is more than 10 volts and Powertrain Control Module (PCM) requests radiator fans to be turned on. DTC may be stored in PCM if an open or short is detected in radiator fan control relay circuit. Possible causes are: defective radiator fan control relay, defective radiator fan, defective PCM, or defective connectors or wiring.
  1. Turn ignition on with engine off. Using scan tool, actuate radiator fan control relay. If both radiator fans cycle on and off, go to next step. If both radiator fans do not cycle on and off, go to step  5 .
  2. Ensure ignition is still on and radiator fan control relay is still actuated. Wiggle wiring harness and connectors between radiator fan control relay and PCM while noting operation of radiator fans. Radiator fan control relay is located near driver's side frame rail. See Fig 1 . PCM is located between driver's side front fender and power distribution center, near battery.
    Fig 1: Locating Radiator Fan Control Relay
    G99F02006Courtesy of DAIMLERCHRYSLER CORPORATION
  3. If cycling of radiator fans was not interrupted while wiggling wiring harness and connectors, go to next step. If cycling of radiator fans was interrupted while wiggling wiring harness and connectors, repair wiring or connectors as necessary. Perform TEST VER-5A  .
  4. Turn ignition off. Inspect wiring harness and connectors between radiator fan control relay, PCM and radiator fans. If no problems exist, test is complete. If any problems exist, repair wiring or connectors as necessary. Perform TEST VER-5A  .
  5. Ensure ignition is still on and radiator fan control relay is still actuated. Using voltmeter, check voltage by backprobing terminal No. 3 (Dark Green wire) on radiator fan control relay connector. Radiator fan control relay is located near driver's side frame rail. See Fig 1 .
  6. If voltage does not cycle from less than one volt to battery voltage, go to next step. If voltage cycles from less than one volt to battery voltage, repair or replace radiator fans or wiring between radiator fan control relay and radiator fans as necessary. Perform TEST VER-5A  .
  7. Turn ignition off. Disconnect radiator fan control relay connector. Turn ignition on with engine off. Using voltmeter, check voltage at terminal No. 4 (Gray wire) on radiator fan control relay connector. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, ensure fuse No. 106 (40-amp) is okay, or repair open on Gray wire between fuse No. 106 and radiator fan control relay. Fuse No. 106 is located in power distribution center at driver's side front corner of engine compartment, near battery. Perform TEST VER-5A  .
  8. Ensure ignition is off and radiator fan control relay connector is disconnected. Using ohmmeter, check resistance between ground and terminal No. 1 (Black wire) on radiator fan control relay connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black wire between radiator fan control relay and ground connection. Ground connection is located on frame rail below battery tray at driver's side front corner of engine compartment. Perform TEST VER-5A  .
  9. Ensure ignition is off. Disconnect PCM connectors. PCM is located between driver's side front fender and power distribution center, near battery.
  10. Ensure radiator fan control relay connector is still disconnected. Using ohmmeter, check resistance between ground and terminal No. 73 (Light Green/Dark Blue wire) on Gray PCM connector C2. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground on Light Green/Dark Blue wire between PCM and radiator fan control relay. Perform TEST VER-5A  .
  11. Using ohmmeter, check resistance between terminal No. 2 (Light Green/Dark Blue wire) on radiator fan control relay connector and terminal No. 73 (Light Green/Dark Blue wire) on Gray PCM connector C2. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Light Green/Dark Blue wire between PCM and radiator fan control relay. Perform TEST VER-5A  .
  12. Ensure ignition is off. Reinstall radiator fan control relay connector. Connect jumper wire to terminal No. 73 (Light Green/Dark Blue wire) on Gray PCM connector C2. Momentarily touch other end of jumper wire to ground and note if radiator fans operate. If radiator fans operate, replace PCM. Perform TEST VER-5A  . If radiator fans do not operate, replace radiator fan control relay. Perform TEST VER-5A  .
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