Diagnostic Aids

Perform this test only when instructed by QUICK TEST or directed by other test procedures. VCRM is located on left side of vehicle, behind front grille. This test is only intended to diagnose the following:

• Variable Control Relay Module (VCRM).
• Powertrain Control Module (PCM).
• Wiring harness circuits associated with VCRM.

  For illustration for VCRM connector terminal identification, see Fig 1 . To prevent replacing good components, be aware that the following unrelated components or systems may be at fault:

  • Ignition Switch, Battery Cables And Ground Straps
  • Alternator And Voltage Regulator
  Fig 1: Identifying VCRM Connector Terminals

  Courtesy of FORD MOTOR CO.

1. 1) Check Battery Supply Power
   
   With Key On Engine Off (KOEO), set DVOM on 20-volt scale. Measure voltage across battery terminals. If voltage is less than 10.5 volts, service or replace discharged battery. If voltage is 10.5 volts or more, go to next step.
2. 2) PCM Ground Fault Isolation
   
   Ensure ignition is off. Install breakout box, and connect PCM. Set DVOM on 20-volt scale. Measure voltage between positive battery terminal and SIG RTN (Gray/Red wire) terminal at Data Link Connector (DLC). See Figure . If voltage is less than 10.5 volts, go to next step. If voltage is 10.5 volts or more, go to step 10).
3. 3) Check Continuity Of SIG RTN Circuit
   
   Turn ignition off. With breakout box installed, disconnect PCM. Measure resistance between breakout box test pin No. 46 and SIG RTN (Gray/Red wire) terminal at DLC. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open SIG RTN circuit. Remove breakout box, and reconnect all components. Repeat QUICK TEST.
4. 4) Check PCM Ground Circuit
   
   Turn ignition off. With breakout box installed and PCM disconnected, measure resistance between negative battery terminal and breakout box test pins No. 40 and 60. If both readings are less than 5 ohms, go to next step. If any reading is 5 ohms or more, repair open in ground circuit. Remove breakout box, and reconnect all components. Repeat QUICK TEST.
5. 5) Check Internal PCM Ground Circuits
   
   Turn ignition off. With breakout box installed, reconnect PCM connector. Measure resistance between test pins No. 46 and 40 and between test pins No. 46 and 60 at breakout box. If resistances are less than 5 ohms, system tests okay. Remove breakout box. Reconnect PCM, and repeat QUICK TEST. If any resistance is 5 ohms or more, replace PCM. Remove breakout box, and reconnect all components. 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) Check Continuity Of VPWR Circuit
   
   Turn ignition off. With breakout box installed, disconnect PCM connector. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between terminal No. 7 (Red wire) at VCRM connector and test pins No. 37 and 57 at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in VPWR circuit between PCM and VCRM. Remove breakout box, and reconnect all components. Repeat QUICK TEST.
7. 11) Check For B+ & IGN START/RUN Power To VCRM
   
   Turn ignition off. With breakout box installed and PCM and VCRM disconnected, measure voltage between terminal No. 6 (Yellow wire) at VCRM wiring harness connector and negative battery terminal. Record voltage reading. Turn ignition on. Measure voltage between terminal No. 17 (Red/Light Green wire) at VCRM wiring harness connector and negative battery terminal. If both readings are 10.5 volts or more, go to next step. If any reading is less than 10.5 volts, turn ignition off. Repair open in B+ or IGN START/RUN circuit. Remove breakout box, and reconnect all components. Repeat QUICK TEST.
8. 12) Check VCRM Ground
   
   Turn ignition off. With breakout box installed and PCM and VCRM disconnected, measure resistance between terminal No. 16 (Black wire) at VCRM wiring harness connector and negative battery terminal. If resistance is less than 5 ohms, replace VCRM. Remove breakout box, and reconnect all components. Repeat QUICK TEST. If resistance is 5 ohms or more, repair open ground circuit. Remove breakout box, and reconnect all components. Repeat QUICK TEST.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 15). No test procedures have been omitted.
9. 15) Continuous Memory Code 584
   
   Continuous Memory Code 584 indicates VCRM PWR GND circuit is open. This could be due to a hard fault or an intermittent condition. Following are possible causes for this fault:
   • Open VCRM PWR GND Circuit
   • Damaged VCRM

   Clear continuous memory. See CLEARING CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Perform KOEO SELF-TEST  . If Code 584 is present (hard code), go to next step. If Code 584 is not present (intermittent), go to step 18).

10. 16) Check Continuity Of VCRM PWR GND Circuit
    
    Turn ignition off. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between terminal No. 1 (Black wire) at VCRM connector and negative battery terminal. If resistance is less than 5 ohms, replace VCRM. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If resistance is 5 ohms or more, repair open ground circuit (Black wire). Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 16) to step 18). No test procedures have been omitted.
11. 18) Check VCRM PWR GND Circuit
    
    Turn ignition off. Visually inspect VCRM PWR GND circuit (Black wire) between terminal No. 1 at VCRM connector and ground. VCRM circuit is grounded at a weld nut on right side of radiator support. Repair wiring as necessary. Start engine. Turn A/C on. Shake, wiggle and bend VCRM PWR GND circuit between VCRM and circuit's ground point. Also, lightly tap on VCRM to simulate road shock. An open circuit will be indicated by fan speed increasing to 100 percent (open circuit must be present for 5 seconds). If an open circuit is detected, isolate fault and repair as necessary. Clear continuous memory (Code 584 should have been set). Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If an open circuit is not detected, turn A/C and ignition off. Go to next step.
12. 19)
    
    Turn ignition off. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Connect a test light between terminal No. 1 (Black wire) and terminal No. 5 (Yellow wire) of VCRM connector. Observe test light, and shake, wiggle and bend VCRM PWR GND circuit between VCRM and circuit's ground point at right side of radiator support. Test light will go out if a fault is detected, indicating an open circuit. If an open circuit is detected, isolate fault and repair as necessary. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If open circuit is not detected, fault is intermittent and cannot be duplicated at this time. Testing is complete. Reconnect all components.
13. 20) Continuous Memory Code 581
    
    Continuous Memory Code 581 indicates that when cooling fan was activated, power to cooling fan circuit exceeded normal current draw. This could be due to a hard fault or an intermittent condition. Following are possible causes for this fault:
    • Short To Ground In Power-To-Cooling Fan Circuit
    • Faulty Cooling Fan Motor
    • Faulty VCRM

    Clear continuous memory. See CLEARING CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Perform KOEO SELF-TEST  . If Code 581 is present (hard code), go to next step. If Code 581 is not present (intermittent), go to step 24).

14. 21) Check Cooling Fan Motor
    
    Clear continuous memory. Disconnect cooling fan motor connector. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Perform KOEO SELF-TEST  . If Code 581 is present, go to next step. If Code 581 is not present, replace cooling fan motor. Reconnect all connectors. Repeat QUICK TEST.
15. 22) Check For Short To Ground In Cooling Fan Circuit
    
    Turn ignition off. Ensure cooling fan motor connector is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between Light Blue wire at cooling fan connector and negative battery terminal. If resistance is more than 10,000 ohms, replace VCRM. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If resistance is 10,000 ohms or less, repair short to ground in Light Blue wire. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 24). No test procedures have been omitted.
16. 24) Check For Intermittent Short To Ground In Cooling Fan Circuit
    
    Turn ignition off. Visually inspect power-to-cooling fan circuit between terminal No. 2 (Light Blue wire) of VCRM connector and cooling fan motor connector. Repair wiring as necessary. Start engine. Turn A/C on. Shake, wiggle and bend power-to-cooling fan circuit between VCRM and cooling fan motor connector. A short to ground will be indicated by cooling fan turning off. Turn A/C and ignition off. If a short to ground is detected, isolate fault and repair as necessary. Clear continuous memory (Code 581 should have been set). Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If a short to ground is not detected, go to next step.
17. 25) Check VCRM Connector & Cooling Fan Circuit
    
    Turn ignition off. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Connect a test light between terminals No. 2 (Light Blue wire) and No. 4 (Yellow wire) at VCRM wiring harness connector. Test light should glow, but not at full brightness. Observe test light, and shake, wiggle and bend power-to-cooling fan circuit (Light Blue wire) near cooling fan. A short to ground is present if test light gets brighter. If a short to ground is detected, isolate fault and repair as necessary. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST.

    If a short to ground is not detected, disconnect and inspect cooling fan connector. Clean or repair connector as necessary. With test light still connected between terminals No. 2 and 4 of VCRM connector, observe test light and repeat power-to-cooling fan circuit wiggle test. If a short to ground is detected (test light gets brighter), isolate fault and repair as necessary. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If a short to ground is not detected, fault is intermittent and cannot be duplicated at this time. Testing is complete. Reconnect all components.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 30). No test procedures have been omitted.
18. 30) Code 582
    
    KOEO Code 582 indicates an open or short to power in cooling fan circuit. Following are possible causes for this fault:
    • Open Or Short To Power In Cooling Fan Circuit
    • Open Cooling Fan Motor Ground Circuit
    • Open Circuit In Cooling Fan
    • Faulty VCRM

    If KOEO Code 587 is also present, repair fault causing KOEO Code 587 to set prior to continuing this test. See the TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section. Ensure cooling fan was not turning during KOEO self-test. If fan was turning, feedback voltage could be sent to VCRM through power-to-cooling fan circuit, resulting in an invalid KOEO Code 582. Ensure engine is cooled down (cooling fan off). Ensure defroster and A/C are off. Turn ignition off. Check cooling fan. If cooling fan is on, go to step 35). If cooling fan is off, go to next step.

19. 31) Check Power-To-Cooling Fan Circuit
    
    Turn ignition off. Disconnect cooling fan connector. Start engine. Turn A/C on. Measure voltage between ground and power-to-cooling fan circuit (Light Blue wire) at cooling fan connector. If voltage is 6 volts or more, turn ignition off. Replace cooling fan. Repeat QUICK TEST. If voltage is less than 6 volts, go to next step.
20. 32) Check Continuity Of Cooling Fan Circuit
    
    Turn ignition off. Ensure cooling fan is disconnected. Measure resistance between ground circuit (Black wire) at cooling fan motor connector and negative battery terminal. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Black wire between cooling fan motor connector and ground. Reconnect cooling fan connector. Repeat QUICK TEST.
21. 33)
    
    Turn ignition off. Ensure cooling fan is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between Light Blue wire at cooling fan motor connector and terminals No. 2 and 3 of VCRM wiring harness connector. If resistance is less than 5 ohms, replace VCRM. Reconnect all components. Repeat QUICK TEST. If resistance is 5 ohms or more, repair open in power-to-cooling fan circuit (Light Blue wire). Reconnect all components. Repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 33) to step 35). No test procedures have been omitted.
22. 35) Check Power To Cooling Fan Circuit For Short To Power
    
    Turn ignition off. Disconnect cooling fan motor connector. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Turn ignition on. Measure voltage between Light Blue wire at cooling fan connector and negative battery terminal. If voltage is less than one volt, replace VCRM. Reconnect all components. Repeat QUICK TEST. If voltage is more than one volt, repair short to power in Light Blue wire. Reconnect all components. Repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 35) to step 40). No test procedures have been omitted.
23. 40) Continuous Memory Code 578
    
    Continuous Memory Code 578 indicates A/C Pressure (ACP) sensor VREF circuit is shorted to ground. This could be due to a hard fault or an intermittent condition. Following are possible causes for this fault:
    • ACP Sensor VREF Circuit Is Shorted To Ground
    • Faulty ACP Sensor
    • Faulty VCRM

    Clear continuous memory. Start engine. Wait 15 seconds. Turn ignition off. Perform KOEO SELF-TEST  . If Code 578 is present (hard code), go to next step. If Code 578 is not present (intermittent), go to step 44).

24. 41) Check ACP Sensor
    
    Clear continuous memory. Turn ignition off. Disconnect ACP sensor connector. Start engine and wait 15 seconds. Turn ignition off. Perform KOEO SELF-TEST  . If Code 578 is present, go to next step. If Code 578 is not present, replace ACP sensor. Clear continuous memory. Start engine and wait 15 seconds. Turn ignition off. Repeat QUICK TEST.
25. 42) Check ACP VREF Circuit For Short To Ground
    
    Ensure ACP sensor is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between ACP VREF circuit (Orange/Light Blue wire) at ACP sensor connector and negative battery terminal. If resistance is more than 10,000 ohms, replace VCRM. Reconnect all components. Clear continuous memory. Start engine and wait 15 seconds. Turn ignition off. Repeat QUICK TEST. If resistance is 10,000 ohms or less, repair short to ground in ACP VREF circuit (Orange/Light Blue wire).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 42) to step 44). No test procedures have been omitted.
26. 44) Check For Intermittent Short To Ground In ACP VREF Circuit
    
    Turn ignition off. Visually inspect ACP VREF circuit between terminal No. 20 (Orange/Light Blue wire) at VCRM connector and ACP sensor connector. Repair wiring as necessary. Disconnect and inspect ACP sensor connector. Clean or repair connector as necessary. Disconnect and inspect VCRM connector. Clean and repair connector as necessary.

    Connect test light between terminals No. 6 (Yellow wire) and No. 20 (Orange/Light Blue wire) at VCRM connector. Observe test light, and shake, wiggle and bend ACP VREF circuit between ACP sensor connector and VCRM connector. If a fault is detected, test light will turn on, indicating a short to ground. If a short to ground is detected, isolate fault and repair wiring as necessary. Reconnect all components. Start engine and wait 15 seconds. Turn ignition off. Repeat QUICK TEST. If a short to ground is not detected, fault is intermittent and cannot be duplicated. Testing is complete. Reconnect all components.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 44) to step 50). No test procedures have been omitted.
27. 50) Continuous Memory Code 579: Check ACP, VREF and ACP SIG RTN Circuits
    
    Continuous Memory Code 579 indicates A/C Pressure (ACP) sensor did not detect a sufficient change in A/C system pressure when A/C system was turned on. This could be due to a problem in ACP sensor circuit or A/C system, and can be a hard fault or an intermittent condition. Following are possible causes for this fault:
    • Open or shorted ACP sensor circuit.
    • Faulty ACP sensor.
    • Faulty VCRM.
    • Power to A/C compressor clutch circuit open. Continuous Memory Code 586 may also be present.

    Turn ignition off. Disconnect ACP sensor. Turn ignition on. Measure voltage between ACP VREF terminal (Orange/Light Blue wire) and ACP SIG RTN terminal (Light Blue/Red wire) at ACP sensor connector. See Fig 2 . If voltage is more than 6 volts, go to step 62). If voltage is less than 4 volts, go to step 63). If voltage is 4-6 volts, go to next step.

    Fig 2: Identifying ACP Sensor Connector Terminals

    Courtesy of FORD MOTOR CO.
28. 51) Check If A/C Compressor Clutch Engages
    
    Turn ignition off. Reconnect ACP sensor. Start engine. Turn A/C on and wait 30 seconds. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step 57).
29. 52) Clear & Attempt To Reset Code 579
    
    Clear continuous memory. Start engine. Turn A/C on and wait until clutch engages. Turn A/C off and wait 5 seconds. Repeat turning A/C on and off 4 more times with each engagement lasting about 20 seconds. Turn A/C and engine off. Repeat KOEO SELF-TEST  . If Code 579 is present, go to next step. If Code 579 is not present, ACP is now functioning. ACP is intermittent or marginal mechanical condition exists in A/C system. Go to step 66).
30. 53) Check A/C System Pressure & Pressure Change
    
    Turn ignition off. Ensure ACP sensor is disconnected. Install A/C system manifold gauge set. With A/C off, start engine. Observe A/C high pressure gauge reading, and turn A/C on. After 10 seconds, note pressure reading. High pressure should increase. If A/C high pressure gauge reading changes by more than 20 psi within 10 seconds of A/C compressor clutch engagement, turn A/C and ignition off and go to next step. If A/C high pressure gauge reading does not change by more than 20 psi within 10 seconds of turning A/C on, check A/C system for mechanical fault. Service A/C system as necessary. Clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only). Repeat QUICK TEST.
31. 54) Check ACP Sensor Output
    
    Turn ignition off. Ensure ACP sensor is disconnected. Connect jumper wires and DVOM between ACP sensor connector halves as shown. See Fig 3 . Start engine and observe voltage reading on DVOM. Turn A/C on and observe voltage reading for 10 seconds after clutch engages. If ACP sensor voltage changes by more than .2 volt within 10 seconds of clutch engagement, sensor is operational. Remove jumper wires and go to step 55).

    If ACP sensor voltage does not change by more than .2 volt within 10 seconds of turning A/C on, replace ACP sensor. Remove A/C system manifold gauge set. Remove jumper wires, and reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST.

    NOTE: Listen to A/C compressor clutch to ensure clutch does not disengage during 10 seconds of testing. If clutch disengages, retest.
    Fig 3: Testing ACP Sensor

    Courtesy of FORD MOTOR CO.
32. 55) Check ACP Circuit For Short To Ground
    
    Turn ignition off. Ensure ACP sensor is disconnected. Disconnect VCRM connector. Measure resistance between ACP circuit terminal (Dark Green/White wire) at ACP sensor wiring harness connector and negative battery terminal. Record resistance reading. Measure resistance between ACP circuit terminal (Dark Green/White) and ACP SIG RTN circuit (Light Blue/Red wire) on ACP sensor wiring harness connector.

    If both readings are more than 10,000 ohms, replace VCRM. Reconnect all components, clear continuous memory, attempt to reset Code 579 (see step 52 for procedure only) and repeat QUICK TEST. If any reading is 10,000 ohms or less, ACP or ACP SIG RTN circuit is shorted to ground. Repair shorted circuit, reconnect all components and clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only) and repeat QUICK TEST.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 55) to step 57). No test procedures have been omitted.
33. 57) Check Voltage To A/C Compressor Clutch
    
    Turn ignition off. Disconnect A/C cyclic pressure switch. Connect a jumper wire between A/C cyclic pressure switch connector terminals. Disconnect A/C compressor clutch connector. Connect a test light between ground and power-to-A/C clutch circuit at A/C clutch wiring harness connector. Start engine. Turn A/C on and wait 10 seconds. If test light is off, go to next step. If test light is on, circuit is okay. Check A/C system for mechanical problems. Reconnect all components and clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only) and repeat QUICK TEST.
34. 58) Check Continuity Of ACP Circuit
    
    Turn ignition off. Ensure ACP sensor is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between ACP signal terminal at ACP connector and terminal No. 19 (Dark Green/White wire) at VCRM wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in ACP circuit (Dark Green/White wire). Remove A/C system manifold gauge set. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST.
35. 59) Check ACP Circuit For Short To ACP VREF
    
    Turn ignition off. Ensure ACP sensor and VCRM are disconnected. Measure resistance between ACP signal terminal (Dark Green/White wire) and ACP VREF terminal (Orange/Light Blue wire) at ACP sensor wiring harness connector. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, ACP signal circuit is shorted to ACP VREF circuit. Repair as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST.
36. 60) Check ACP Circuit For Short To Power
    
    Turn ignition off. Ensure ACP sensor and VCRM are disconnected. Turn ignition on. Measure voltage between ACP signal terminal (Dark Green/White wire) at ACP sensor wiring harness connector and negative battery terminal. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to power in ACP circuit. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST.
37. 61) Check If Test Light Will Glow With ACP Circuit Grounded
    
    Turn ignition off. Ensure ACP sensor is disconnected. Reconnect VCRM. Disconnect A/C cyclic pressure switch. Connect a jumper wire between A/C cyclic pressure switch connector terminals. Disconnect A/C compressor clutch connector. Connect a test light between wiring harness side of A/C compressor clutch connector terminals. Connect a jumper wire between ACP circuit (Dark Green/White wire) and negative battery terminal. Start engine. Turn A/C on and wait 10 seconds. Observe test light.

    If test light is on, replace ACP sensor. Turn A/C off. Reconnect all components. Clear continuous memory. Start engine and turn A/C on for 20 seconds then turn ignition off. Repeat QUICK TEST. If test light is off, replace VCRM. Reconnect all components. Clear continuous memory. Start engine and turn A/C on for 20 seconds then turn ignition off. Repeat QUICK TEST.

38. 62) Check For Short To Power In ACP VREF Circuit
    
    Turn ignition off. Ensure ACP sensor is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Turn ignition on. Measure voltage between ACP VREF terminal (Orange/Light Blue wire) at ACP sensor connector and negative battery terminal. If voltage is less than one volt, replace VCRM. Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for procedure only) and repeat QUICK TEST. If voltage is more than one volt, repair short to power in ACP VREF circuit (Orange/Light Blue wire). Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for procedure only) and repeat QUICK TEST.
39. 63) Check Continuity Of ACP SIG RTN & VREF Circuits
    
    Turn ignition off. Ensure ACP sensor is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Measure resistance between ACP SIG RTN terminal (Light Blue/Red wire) at ACP sensor connector and terminal No. 12 (Light Blue/Red wire) at VCRM wiring harness connector. Record resistance reading. Measure resistance between ACP VREF terminal (Orange/Light Blue wire) at ACP sensor connector and terminal No. 20 (Orange/Light Blue wire) at VCRM wiring harness connector. Record resistance reading. If both readings are less than 5 ohms, go to next step. If any reading is 5 ohms or more, repair open in ACP VREF circuit (Orange/Light Blue wire) or ACP SIG RTN circuit (Light Blue/Red wire). Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only). Repeat QUICK TEST.
40. 64) Check ACP SIG RTN Circuit For Short To VREF
    
    Turn ignition off. Ensure ACP sensor and VCRM connectors are disconnected. Measure resistance between ACP SIG RTN terminal (Light Blue/Red wire) and ACP VREF terminal (Orange/Light Blue wire) at ACP connector. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, ACP SIG RTN circuit is shorted to ACP VREF circuit. Repair wiring as necessary. Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only). Repeat QUICK TEST.
41. 65) Check For Short To Power In ACP SIG RTN Circuit
    
    Turn ignition off. Ensure ACP sensor and VCRM connectors are disconnected. Turn ignition on. Measure voltage between ACP SIG RTN terminal (Light Blue/Red wire) at ACP sensor connector and negative battery terminal. If voltage is less than one volt, replace VCRM. Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for procedure only). Repeat QUICK TEST. If voltage is one volt or more, repair short to power in ACP SIG RTN circuit (Light Blue/Red wire). Reconnect all components. Clear continuous memory. Attempt to reset Code 579 (see step 52 for reset procedure only). Repeat QUICK TEST.
42. 66) Check A/C Cooling Performance
    
    Check A/C system performance. If A/C system cools properly, go to next step. If A/C system does not cool properly, check mechanical condition of A/C system. If mechanical condition is okay, go to next step.
43. 67) Check For Intermittent Open In ACP VREF & ACP SIG RTN Circuits
    
    Turn A/C and ignition off. Disconnect and inspect ACP sensor connector. Clean or repair connector as necessary. Turn ignition on. Connect test light between ACP VREF terminal (Orange/Light Blue wire) and ACP SIG RTN terminal (Light Blue/Red wire) at ACP sensor connector. Test light should turn on.

    If test light does not glow sufficiently, a DVOM may be used instead of test light to monitor 5-volt reference signal. Observe test light/DVOM, and shake, wiggle and bend ACP VREF and ACP SIG RTN circuits between ACP sensor connector and VCRM connector. If a fault is detected, test light will turn off or DVOM voltage will drop, indicating an open circuit. If an open circuit is detected, isolate fault and repair wiring as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If open circuit is not detected, go to next step.

44. 68) Check ACP Signal Circuit For Intermittent Short
    
    Turn ignition off. Ensure ACP sensor is disconnected. Connect test light or DVOM between ACP VREF terminal (Orange/Light Blue wire) and ACP signal terminal (Dark Green/White wire) at ACP sensor connector. Test light should be off or DVOM reading should be zero volts. Observe test light/DVOM, and shake, wiggle and bend ACP signal circuit (Dark Green/White wire) between ACP sensor connector and VCRM connector. Lightly tap on VCRM to simulate road shock. If a fault is detected, test light will turn on or DVOM reading will show 5 volts, indicating a short to ground. If a short to ground is detected, isolate fault and repair wiring as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST.

    If a short to ground is not detected, remove test light/DVOM. Reconnect test light/DVOM between ACP SIG RTN terminal (Light Blue/Red wire) and ACP signal terminal (Dark Green/White wire) at ACP sensor connector. Observe test light/DVOM, and repeat wiggle test of ACP signal circuit. If a fault is detected, test light will turn on or DVOM reading will show 5 volts, indicating a short to power. If short to power is not detected, go to next step. If a short to power is detected, isolate fault and repair wiring as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST.

45. 69) Check ACP Signal Circuit For Intermittent Open
    
    Turn ignition off. Ensure ACP sensor is disconnected. Disconnect and inspect VCRM connector. Clean or repair connector as necessary. Using a DVOM, measure resistance of Dark Green/White wire between terminal No. 19 at VCRM connector and ACP signal terminal at ACP sensor connector. If resistance is 5 ohms or more, isolate fault and repair wiring as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST.

    If resistance is less than 5 ohms, observe DVOM, and shake, wiggle and bend ACP signal circuit (Dark Green/White wire) between ACP sensor connector and VCRM connector. If a fault is detected, DVOM reading will show 5 ohms or more, indicating an open circuit. If an open circuit is detected, isolate fault and repair wiring as necessary. Reconnect all components. Clear continuous memory. Start engine. Turn A/C on and wait 20 seconds. Turn A/C and ignition off. Repeat QUICK TEST. If an open circuit is not detected, fault is intermittent and cannot be duplicated at this time. Reconnect all components.