Diagnostic Aids

Perform this test only when instructed during QUICK TEST or other test step. Go to QUICK TEST. See G - TESTS W/ CODES or G - TESTS W/ CODES (Town Car) article in ENGINE PERFORMANCE section. This test is only intended to diagnose the following:

• Harness circuits (VPWR, B+, FC, HFC, LFC, IGN START/RUN and Power-To-Fan(s).
• Fan Control (FC) relay.
• Low Speed Fan Control (LFC) relay.
• High Speed Fan Control (HFC) relay.
• Powertrain Control Module (PCM).
  CIRCUIT PIN IDENTIFICATION
  
  

  DTC	Circuit/Relay	Breakout Box Pin No.
  P1474	FC	45

1. 1) KOEO/KOER DTC P1474 & P1479: Check For VPWR To Applicable Fan Control Relay
   
   DTC P1474 indicates a Low Speed Fan Control (LFC) or Fan Control (FC) primary circuit failure. DTC P1479 indicates a High Speed Fan Control (HFC) primary circuit failure. Possible causes are:
   • Open or shorted FC, LFC or HFC circuit.
   • Open VPWR circuit to fan control relay.
   • Faulty fan control relay (FC, LFC or HFC).
   • Faulty PCM.

   Turn ignition off. Disconnect appropriate fan control relay. Turn ignition on. Using a voltmeter, check voltage between VPWR circuit at appropriate fan control relay harness connector and negative battery terminal. If reading is greater than 10.5 volts, go to next step. If reading is not as specified, repair open in VPWR circuit to appropriate fan control relay. Reconnect fan control relay. Repeat QUICK TEST.

2. 2) Check For FC, LFC Or HFC Circuit Cycling
   
   Install scan tool. Turn ignition on, engine off. Disconnect appropriate fan control relay. Access OUTPUT TEST MODE on scan tool. Connect a test light between VPWR circuit and FC, LFC or HFC circuit at appropriate fan control relay harness connector. Using scan tool, command appropriate cooling fan speed on, then off. If test light toggles on, then off, replace appropriate fan control relay. Repeat QUICK TEST. If operation is not as specified, turn ignition off, remove test light and go to next step.
3. 3) Check FC, LFC Or HFC Circuit For Short To Power
   
   Turn ignition off. Disconnect appropriate fan control relay. Disconnect PCM harness connectors. Check for corroded, damaged or backed-out terminal pins. Repair as necessary. Turn ignition on, engine off. Using a voltmeter, check voltage between FC, LFC or HFC circuit at appropriate fan control relay harness connector and negative battery terminal. Turn Ignition off. If reading is less than one volt with ignition on or off, go to next step. If reading is not as specified, repair FC, LFC or HFC circuit for short to power. Reconnect all components and repeat QUICK TEST. If operation is not as specified, turn ignition off, remove test light and go to next step.
4. 4) Check FC, LFC Or HFC Circuit For Short To Ground
   
   Turn ignition off. Disconnect scan tool. Disconnect appropriate fan control relay. Disconnect PCM harness connectors. Install breakout box, leaving PCM disconnected. Using an ohmmeter, check resistance between appropriate fan control circuit test pin (FC, LFC or HFC) and test pins No. 51, 91 and 103 at breakout box. If each resistance is greater than 10 k/ohms, go to next step. If resistance is not as specified, repair fan control circuit that is shorted to ground. Remove breakout box. Reconnect all components and repeat QUICK TEST.
5. 5) Check FC, LFC Or HFC Circuit Resistance
   
   Turn ignition off. Disconnect appropriate fan control relay. Install breakout box, leaving PCM disconnected. Using an ohmmeter, check resistance between appropriate fan control circuit test pin (FC, LFC or HFC) at breakout box and FC, LFC or HFC circuit at appropriate fan control relay harness connector. If resistance is less than 5 ohms, replace PCM. If resistance is not as specified, repair open in FC, LFC or HFC circuit. Remove breakout box. Reconnect all components and repeat QUICK TEST.
   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 FC or LFC circuit failure occurred during vehicle operation. Possible causes are:
   • Open VPWR circuit to FC or LFC relay.
   • Open or shorted FC or LFC circuit.

   Turn ignition off. Ensure A/C and defroster are off. Install scan tool. Disconnect cooling fan motor harness connector(s). Check for corroded, damaged or backed-out terminal pins. Repair as necessary. Connect a test light between Power-To-Fan circuit and ground circuit at fan motor harness connector. Turn ignition on, engine off. Using scan tool, access OUTPUT TEST MODE. 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 FC or LFC circuit between PCM and FC or LFC relay.
   • Shake and bend VPWR or IGN START/RUN circuit to FC or LFC relay.
   • Lightly tap on FC or LFC relay to simulate road shock.

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

7. 11) Check FC Or LFC Circuit For Short To Ground
   
   Turn ignition on, engine off. Ensure cooling fan motor harness connector(s) are disconnected and test light is still installed. 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 FC or LFC circuit between PCM and FC or LFC relay.
   • Lightly tap on FC or LFC relay to simulate road shock.

   If fault is indicated, isolate and repair short to ground in wiring harness. Repeat QUICK TEST. If fault is not indicated, problem may be intermittent. Go to CIRCUIT TEST Z. See G - TESTS W/ CODES or G - TESTS W/ CODES (Town Car) article in ENGINE PERFORMANCE section.

   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.