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Home >> Mazda >> 1999 >> B2500 SX, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Engine Controls - Self-Diagnostics - EEC-V - 6.8L (99S E Series & 99S F350 To F550)) >> System Tests >> Test KF: Fan Control (FC) Relay >> Diagnostic Aids

Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

This system test is for Contour, Crown Victoria, Grand Marquis, Mystique, Sable, Taurus, Town Car and Windstar only. On all models, PCM determines engine cooling fan requirements and controls fan operation through Low Fan Control (LFC) and High Fan Control (HFC) circuits. HFC relay is normally open.

Perform this test only when instructed by QUICK TEST or directed by other test procedures. This test is only intended to diagnose:

Fig 1: Identifying LFC/HFC Circuits (Continental, Sable & Taurus)
G99F02676Courtesy of FORD MOTOR CO.
Fig 2: Identifying LFC/HFC Circuits (Contour & Mystique)
G99A02674Courtesy of FORD MOTOR CO.
Fig 3: Identifying Cooling Fan Relay Circuits (Crown Victoria, Grand Marquis & Town Car)
G99C02670Courtesy of FORD MOTOR CO.
Fig 4: Identifying LFC/HFC Circuits (Windstar)
G99G02672Courtesy of FORD MOTOR CO.

  1. 1) DTC P1474 & P1479: Check For VPWR To Applicable Fan Control Relay

    DTC P1474 indicates a Low Speed Fan Control (LFC) primary circuit failure. DTC P1479 indicates a High Speed Fan Control (HFC) primary circuit failure. Possible causes are:
    • Open or shorted LFC or HFC circuit.
    • Open VPWR circuit to fan control relay.
    • Faulty fan control relay (LFC or HFC).
    • Faulty PCM.

    Turn ignition off. Disconnect appropriate fan control relay. Turn ignition on. Using a voltmeter, measure voltage between VPWR terminal at appropriate fan control relay wiring harness connector and negative battery terminal. See Fig 1-Fig 4 . If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit to appropriate fan control relay.

  2. 2) Check For LFC Or HFC Circuit Cycling

    Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Connect a test light between VPWR terminal and LFC or HFC terminal at appropriate fan control relay wiring harness connector. Using scan tool, command appropriate cooling fan speed on and off. If test light turns on and off, replace appropriate fan control relay. If test light does not turn on and off, turn ignition off, remove test light and go to next step.

  3. 3) Check LFC Or HFC Circuit For Short To Power

    Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on, engine off. Measure voltage between ground and LFC or HFC terminal at appropriate fan control relay wiring harness connector. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair LFC or HFC circuit for short to power.

  4. 4) Check LFC Or HFC Circuit For Short To Ground

    Turn ignition off. Disconnect scan tool from DLC. Measure resistance between ground and LFC or HFC terminal at appropriate fan control relay wiring harness connector. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair LFC or HFC circuit short to ground.

  5. 5) Check For Open LFC Or HFC Circuit

    Measure resistance between appropriate PCM connector pin (LFC or HFC) and LFC or HFC terminal at appropriate fan control relay wiring harness connector. If resistance is less than 5 ohms, replace PCM. If resistance 5 ohms or more, repair open in LFC or HFC circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 5) to step 10). No test procedures have been omitted.

  6. 10) Continuous Memory DTC P1474

    Continuous Memory DTC P1474 indicates an LFC circuit failure occurred during vehicle operation. Possible causes are:
    • Open VPWR circuit to LFC relay.
    • Open or shorted LFC circuit.

    Turn ignition off. Ensure A/C and defroster are off. Disconnect cooling fan motor connector (both fan motor connectors on models with 2 fans). Inspect connector(s) for loose, damaged or corroded terminals. Repair as necessary. Connect a test light between ground and power-to-low fan terminal at fan motor wiring harness connector (either connector on models with 2 fans). Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Command low speed fan ON. Test light should be on. Observe test light for indication of fault (test light will turn off to indicate fault) while performing the following:

    • Shake and bend LFC circuit between PCM and LFC relay.
    • Shake and bend VPWR circuit to LFC relay.
    • Lightly tap on LFC relay to simulate road shock.

    If fault is indicated, turn ignition off. Isolate and repair open or short to power in wiring harness. If fault is not indicated, go to next step.

  7. 11) Check LFC Circuit For Short To Ground

    Turn ignition on, engine off. Ensure cooling fan motor connector(s) are disconnected and test light is still connected. Using scan tool, command low speed fan OFF. Test light should be off. Observe test light for indication of fault (test light will turn on to indicate fault) while performing the following:
    • Shake and bend LFC circuit between PCM and LFC relay.
    • Lightly tap on LFC relay to simulate road shock.

    If fault is indicated, isolate and repair short to ground in wiring harness. If fault is not indicated, problem is intermittent. Go to TEST Z .

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 20). No test procedures have been omitted.

  8. 20) Continuous Memory DTC P1479

    Continuous Memory DTC P1479 indicates an HFC circuit failure has occurred during vehicle operation. Possible causes are:
    • Open VPWR circuit to HFC relay.
    • Open or shorted HFC circuit.

    Turn ignition off. Ensure A/C and defroster are off. Disconnect cooling fan motor connector (both fan motor connectors on models with 2 fans). Inspect connector(s) for loose, damaged or corroded terminals. Repair as necessary. Connect a test light between ground and HIGH FAN PWR terminal at fan motor wiring harness connector (either connector on models with 2 fans). Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Command high speed fan ON. Test light should be on. Observe test light for indication of fault (test light will turn off to indicate fault) while performing the following:

    • Shake and bend HFC circuit between PCM and HFC relay.
    • Shake and bend VPWR circuit to HFC relay.
    • Lightly tap on HFC relay to simulate road shock.

    If fault is indicated, turn ignition off. Isolate and repair open or short to power in wiring harness. If fault is not indicated, go to next step.

  9. 21) Check HFC Circuit For Short To Ground

    Turn ignition on, engine off. Ensure cooling fan motor connector(s) are disconnected and test light is still installed. Using scan tool, command high speed fan OFF. Test light should be off. Observe test light for indication of fault (test light will turn on to indicate fault) while performing the following:
    • Shake and bend HFC circuit between PCM and HFC relay.
    • Lightly tap on HFC fan control relay to simulate road shock.

    If fault is indicated, turn ignition off. Isolate and repair short to ground in wiring harness. If fault is not indicated, problem is intermittent. Go to TEST Z .

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 21) to step 30). No test procedures have been omitted.

  10. 30) Electric Cooling Fan Problem (With No DTCs)

    Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Command cooling fan ON and check fan operation. On models with 2-speed fan, check both fan speeds. Wait 20 seconds after commanding high fan speed on. Verify fan changes speed. On all models, if fan(s) functions properly, turn ignition off. Return to test that directed you here. If fan(s) do not function properly, go to step  50) (Contour, Cougar, Mystique and Windstar) or go to next step (all other models).

  11. 31) Determine Fan Operation

    During operational check of both fan speeds, if cooling fan(s) operated at one speed only, go to step  40). If cooling fan(s) did not operate at any speed, go to next step. On Sable and Taurus, if one cooling fan did not operate properly, but other fan operated properly, go to step  70).

  12. 32) Cooling Fan Will Not Operate At Any Speed

    Ensure ignition is on, scan tool is still connected and in OUTPUT TEST MODE , and cooling fan is commanded off. Disconnect cooling fan motor connector (both fan motor connectors on Sable and Taurus). Using scan tool, command high speed cooling fan ON. Using a voltmeter, measure voltage between ground and HIGH FAN PWR terminal at fan motor wiring harness connector (either connector on Sable and Taurus). If voltage is 10 volts or less, go to next step. If voltage is more than 10 volts, go to step  37).

  13. 33) Check B+ Circuit To HFC & LFC Relays

    Turn ignition off. Ensure cooling fan motor connector(s) are disconnected. Disconnect HFC and LFC relays. Measure voltage between ground and B+ terminal at HFC and LFC relay wiring harness connectors. If both voltage readings are more than 10.5 volts, go to next step. If any voltage reading is 10.5 volts or less, check for faulty B+ circuit (open circuit or blown fuse). If a fuse is blown, check for short to ground before replacing fuse. Repair as necessary. Recheck cooling fan operation.

  14. 34) Check For Open Circuit

    Measure resistance of HIGH FAN PWR circuit between HFC relay wiring harness connector and cooling fan motor wiring harness connector(s). Also measure resistance of LOW FAN PWR circuit between LFC relay wiring harness connector and cooling fan wiring harness connector(s). If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, locate and repair open circuit. Recheck cooling fan operation.

  15. 35) Check Power To Cooling Fan Motor

    Reconnect HFC and LFC relays. Ensure cooling fan motor connector(s) are disconnected. Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE . Command low speed fan ON. Measure voltage between ground and LOW FAN PWR terminal at cooling fan motor wiring harness connector (either connector on Sable and Taurus). If voltage is more than 10 volts, replace HFC relay and go to step  37). If voltage is 10 volts or less, go to step  75) and follow procedure for low speed fan inoperative. After repair, repeat step  75) and follow procedure for high speed fan inoperative.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 35) to step 37). No test procedures have been omitted.

  16. 37) Check Cooling Fan Ground Circuit

    Turn ignition off. Disconnect scan tool. Measure resistance between ground and ground terminal at cooling fan motor wiring harness connector. If resistance is less than 5 ohms, replace cooling fan motor(s). If resistance is 5 ohms or more, locate and repair open in ground circuit. Recheck cooling fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 37) to step 40). No test procedures have been omitted.

  17. 40) Determine Which Fan Speed Is Operational (Escort, Mustang &Tracer)

    If high speed fan was inoperative in step 31)  , go to step 46)  . If low speed fan was inoperative in step 31)  , go to next step.

  18. 41) Low Speed Fan Inoperative

    Turn ignition on, engine off. Ensure scan tool is still in OUTPUT TEST MODE  with fan commanded off. Disconnect cooling fan motor connector (both connectors on Sable and Taurus). Using scan tool, command low speed fan ON. Measure voltage between ground and LOW FAN PWR terminal at cooling fan motor wiring harness connector (either connector on Sable and Taurus). If voltage is more than 10 volts, verify ground circuit to cooling fan motor. If ground is okay, replace fan motor and recheck cooling fan operation. If voltage is 10 volts or less, go to next step.

  19. 42) Check Voltage To LFC Relay

    Disconnect LFC relay. Measure voltage between ground and B+ terminal at LFC relay wiring harness connector. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check for faulty B+ circuit (open circuit or blown fuse). If a fuse is blown, check for short to ground before replacing fuse. Repair as necessary. Recheck cooling fan operation.

  20. 43) Check For Open Circuit

    Measure resistance of LOW FAN PWR circuit between LFC relay wiring harness connector and cooling fan motor wiring harness connector(s). If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, locate and repair open in LOW FAN PWR circuit. Recheck cooling fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 43) to step 46). No test procedures have been omitted.

  21. 46) High Speed Fan Inoperative

    Ensure scan tool is connected and still in OUTPUT TEST MODE with fan commanded off. Disconnect cooling fan motor connector (both connectors on Sable and Taurus). Turn ignition on, engine off. Using scan tool, command high speed fan ON. Measure voltage between ground and HIGH FAN PWR terminal at cooling fan motor wiring harness connector. If voltage is more than 10 volts, verify ground circuit to cooling fan motor. If ground is okay, replace fan motor and recheck cooling fan operation. If voltage is 10 volts or less, go to next step.

  22. 47) Check For B+ To HFC Relay

    Disconnect HFC relay. Measure voltage between ground and B+ terminal at HFC relay wiring harness connector. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, locate cause of no B+ to HFC relay (blown fuse or open circuit). If fuse is blown, check for short circuit before replacing fuse. Repair as necessary. Recheck cooling fan operation.

  23. 48) Check For Open High Fan PWR Circuit

    Turn ignition off. Measure resistance of HIGH FAN PWR circuit between HFC relay wiring harness connector and cooling fan motor wiring harness connector. If resistance is less than 5 ohms, go to step  75). If resistance is 5 ohms or more, repair open in HIGH FAN PWR circuit. Recheck cooling fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 48) to step 50). No test procedures have been omitted.

  24. 50) Low Speed &/Or High Speed Cooling Fan Inoperative (Contour, Cougar, Mystique & Windstar)

    If one cooling fan is inoperative, but other cooling fan operates normally, go to step  70). Turn ignition off. Disconnect LFC and HFC relays. Measure voltage between ground and B+ terminal at both LFC and HFC relay wiring harness connectors. If both voltage readings are more than 10.5 volts, go to next step. If any voltage reading is 10.5 volts or less, locate and repair open in B+ circuit. If fuse or fuse link was blown, check and repair cause of blown fuse or fuse link. Recheck cooling fan operation.

  25. 51) Check Fan PWR Circuit, Fan Ground & Internal Fan Circuits

    Ensure ignition is off. Measure resistance between ground and FAN PWR terminal at both LFC and HFC relay wiring harness connectors. If both resistance readings are less than 15 ohms, go to next step. If any resistance reading is 15 ohms or more, go to step  56).

  26. 52) Check For Short To Ground In Fan PWR Circuit

    Disconnect both cooling fan motors. Measure resistance between ground and FAN PWR terminal at HFC relay wiring harness connector. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, locate and repair short to ground in FAN PWR circuit. Recheck cooling fan operation.

  27. 53) Check HFC & LFC Relay Operation

    Ensure cooling fan motor connectors are disconnected. Reconnect HFC and LFC relays. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Check relays as follows:

    • HFC Relay

      Turn ignition on, engine off. Using scan tool, command high speed fan ON. Wait 15 seconds. Using a voltmeter, measure voltage between ground and FAN PWR terminal at cooling fan motor wiring harness connector (either fan motor). Voltage should be more than 10.5 volts.

    • LFC Relay

      Turn ignition on, engine off. Using scan tool, command low speed fan ON. Using a voltmeter, measure voltage between ground and FAN PWR terminal at cooling fan motor wiring harness connector (either fan motor). Voltage should be more than 10 volts.

    If both voltage readings are as specified, replace cooling fan motor(s). If any voltage reading is not as specified, note which fan speed is inoperative and go to step  75).

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 53) to step 56). No test procedures have been omitted.

  28. 56) Check Fan PWR Circuit Resistance

    Turn ignition off. Disconnect cooling fan motor (either one). Measure resistance of FAN PWR circuit between cooling fan motor wiring harness connector and both HFC and LFC relay wiring harness connectors. If both resistance readings are less than 15 ohms, go to next step. If any resistance reading is 15 ohms or more, locate and repair open in FAN PWR circuit. Recheck cooling fan operation.

  29. 57) Check Cooling Fan Ground Circuit

    Measure resistance between ground and ground terminal at cooling fan motor wiring harness connector. If resistance is less than 5 ohms, replace inoperative cooling fan motor(s). If resistance is 5 ohms or more, locate and repair open in ground circuit. Recheck cooling fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 57) to step 60). No test procedures have been omitted.

  30. 60) Low &/Or High Speed Cooling Fan Always Runs (No DTCs): Verify Fan Is Not On Because Of A/C High Pressure Switch Input To PCM

    Start engine. Using scan tool, select ACP PID from PID/DATA monitor menu. If PID value indicates CLOSED, leave engine running and go to next step. If PID value indicates OPEN, go to step  65).

  31. 61) Check A/C High Pressure Switch

    Disconnect A/C high pressure switch. Again, check ACP PID value. If PID value indicates CLOSED, turn ignition off and go to next step. If PID value indicates OPEN, turn ignition off and reconnect A/C high pressure switch. Service A/C system as necessary.

  32. 62) Check For Short To Ground In ACPSW Circuit

    Disconnect scan tool from DLC. Disconnect PCM connector. Measure resistance between PCM connector pin No. 86 and ground. If resistance is more than 10,000 ohms, replace PCM. If resistance is 10,000 ohms or less, repair short to ground in ACPSW circuit.

  33. 63) Low &/Or High Speed Cooling Fan Always Runs (No DTCs): Verify Fan Is Not On Because Of A/C High Pressure Sensor Input To PCM

    Turn A/C off. Start engine. Using scan tool, select ACP V PID from PID/DATA monitor menu. If PID voltage indicates more than 3 volts, turn ignition off. Service A/C system as necessary. If PID voltage is 3 volts or less, go to next step.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 63) to step 65). No test procedures have been omitted.

  34. 65) Low &/Or High Speed Cooling Fan Always Runs

    Turn A/C and defroster off. Turn ignition off. Disconnect LFC relay. Turn ignition on. If cooling fan continues to run, go to next step. If cooling fan stops, go to step  80).

  35. 66) Check HFC Relay

    Turn ignition off. Disconnect HFC and LFC relays. Turn ignition on. Check cooling fan operation. If cooling fan stops, go to step  80). If cooling fan remains on, turn ignition off. On Contour, Cougar, Mystique and Windstar, repair FAN PWR circuit for short to power. Recheck cooling fan operation. On all other models, go to next step.

  36. 67) Check Low Fan PWR Circuit For Short To Power

    Turn ignition off. Disconnect cooling fan motor connector (both fan motor connectors on Sable and Taurus). Turn ignition on. Measure voltage between ground and LOW FAN PWR terminal at cooling fan motor wiring harness connector. If voltage is less than one volt, repair HIGH FAN PWR circuit for short to power. Recheck cooling fan operation. If voltage is one volt or more, repair LOW FAN PWR circuit for short to power. Recheck fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 67) to step 70). No test procedures have been omitted.

  37. 70) One Cooling Fan Inoperative & Other Cooling Fan Operates Normal (No DTCs)

    Turn ignition off. Disconnect inoperative cooling fan motor connector. Measure resistance between ground and ground terminal at fan motor wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in ground circuit. Recheck cooling fan operation.

  38. 71) Check For Voltage To Fan

    Disconnect remaining cooling fan motor. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Command high speed fan ON. Measure voltage between ground and HIGH FAN PWR terminal at inoperative cooling fan motor wiring harness connector. On Sable and Taurus, also command low speed fan ON. Measure voltage between ground and LOW FAN PWR terminal at inoperative cooling fan motor wiring harness connector. On all models, if voltage is more than 10 volts (at both terminals on Sable and Taurus), replace inoperative cooling fan motor. Recheck cooling fan operation. If voltage is 10 volts or less, locate and repair open circuit between inoperative cooling fan motor and splice to other fan motor. Recheck fan operation.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 71) to step 75). No test procedures have been omitted.

  39. 75) Accessing Parameter Identification (PID)

    A inoperative high speed or low speed fan can be caused by a primary circuit fault, even though a DTC was not set. Check if scan tool being used is capable of accessing PID values while in Output Test Mode. If PID access is possible, go to next step. If PID access is not possible, go to step  78) (if low speed fan inoperative) or step  79) (if high speed fan inoperative).

  40. 76) Check Operation Of Primary Fan Circuits

    Reconnect all connectors. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Perform the appropriate test procedure as follows:

    • Low Speed Fan Inoperative

      Using scan tool, select LFCA and LFCF PIDs from PID/DATA monitor menu. With low speed fan off, LFCA PID should read OFF and LFCF PID should read NO. Command low speed fan ON. LFCA PID should read ON and LFCF PID should still be NO.

    • High Speed Fan Inoperative

      Using scan tool, select HFCA and HFCF PIDs from PID/DATA monitor menu. Command high speed fan ON. HFCA PID should read OFF and LFCF PID should read NO. Command high speed fan ON. HFCA PID should read ON and HFCF PID should still be NO.

    If LFCF PID of HFCF PID indicated YES with fan commanded on or off, a primary circuit fault is detected. Go to step  1) and perform diagnosis for DTC P1479 (if HFCF PID was yes) or perform diagnosis for DTC P1474 (if LFCF PID was yes). If LFCF PID of HFCF PID indicated NO with fan commanded on or off, primary circuits are okay. Replace LFC relay (if low speed fan is inoperative) or replace HFC relay (if high speed fan is inoperative). Verify applicable FAN PWR circuit is not shorted to ground. Recheck cooling fan operation.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 76) to step 78). No test procedures have been omitted.

  41. 78) Check Operation Of Low Speed Fan Primary Circuits

    Reconnect all connectors. Turn ignition on. Connect a test light between VPWR terminal and LFC terminal at LFC relay wiring harness connector. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. While observing scan tool, command low speed fan ON then OFF. If test light turns on then off, primary circuits are okay. Replace LFC relay. Verify FAN PWR circuit is not shorted to ground. Recheck cooling fan operation. If test light did not turn on then off, LFC primary circuit fault is detected. Go to step  1) and perform diagnosis for DTC P1474.

  42. 79) Check Operation Of High Speed Fan Primary Circuits

    Reconnect all connectors. Turn ignition on. Connect a test light between VPWR terminal and HFC terminal at HFC relay wiring harness connector. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. While observing scan tool, command high speed fan ON then OFF. If test light turns on then off, primary circuits are okay. Replace HFC relay. Verify FAN PWR circuit is not shorted to ground. Recheck cooling fan operation. If test light did not turn on then off, HFC primary circuit fault is detected. Go to step  1) and perform diagnosis for DTC P1479.

  43. 80) Check Operation Of Primary Fan Circuits

    A inoperative high speed or low speed fan can be caused by a primary circuit fault, even though a DTC was not set. Reconnect LFC or HFC relay connector. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  in ADDITIONAL SYSTEM FUNCTIONS. Perform the appropriate test procedure as follows:

    • Fan Stops Running With LFC Relay Disconnected

      Using scan tool, select LFCA and LFCF PIDs from PID/DATA monitor menu. Command low speed OFF. LFCA PID should read OFF and LFCF PID should read NO.

    • Fan Stops Running With HFC Relay Disconnected

      Using scan tool, select HFCA and HFCF PIDs from PID/DATA monitor menu. Command high speed fan OFF. HFCA PID should read OFF and HFCF PID should read NO.

    If LFCF PID of HFCF PID indicated YES with fan commanded OFF, a primary circuit fault is detected. Go to step  1) and perform diagnosis for DTC P1479 (if HFCF PID was yes) or perform diagnosis for DTC P1474 (if LFCF PID was yes). If LFCF PID of HFCF PID indicated NO with fan commanded OFF, primary circuits are okay. Replace LFC relay (if fan stopped running with LFC relay disconnected) or replace HFC relay (if fan stopped running with HFC relay disconnected). Recheck cooling fan operation.

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