Diagnostic Aids

Perform this test only when instructed to. VLCM is located on lower front center of engine compartment. This test is only intended to diagnose the following:

• Variable Load Control Module (VLCM).
• Wiring harness circuits associated with VLCM.
• Powertrain Control Module (PCM).

Fig 1: Identifying VLCM Connector Terminals

Fig 2: VLCM Schematic & Test Circuits

1. 1) DTC P1484: Attempt To Regenerate DTC
   
   DTC P1484 indicates an open VLCM PWR GND circuit (terminal No. 1). Possible causes are an open VLCM PWR GND circuit or faulty VLCM. Clear DTCs. Start engine, turn A/C on and wait 15 seconds. Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1484 is present (hard code), go to next step. If Continuous Memory DTC P1484 is not present (intermittent), go to step 4).
2. 2) Check VLCM PWR GND Circuit
   
   Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance terminal No. 1 (Black wire) at VLCM wiring harness connector negative battery terminal. If resistance is less than 5 ohms, replace VLCM. Reconnect all components. Clear DTCs. 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, locate and repair open in VLCM PWR GND 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.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 2) to step 4). No test procedures have been omitted.
3. 4) Check VLCM PWR GND For Intermittents
   
   Visually check VLCM PWR GND circuit between VLCM terminal No. 1 and ground junction. Ground junction is located in right front corner of engine compartment, on front fender apron. Connect a non-powered test light between terminals No. 1 (Black wire) and No. 15 (Red wire) at VCRM wiring harness connector. 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 VLCM PWR GND circuit (Black wire) between VLCM and ground junction.

   If fault is indicated, isolate and repair open in PWR GND circuit. Reconnect all components. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST . If fault is not indicated, problem is intermittent and cannot be duplicated at this time. Go to CIRCUIT TEST Z .

   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 10). No test procedures have been omitted.
4. 10) DTC P1483: Attempt To Regenerate DTC
   
   DTC P1483 indicates that when cooling fan was activated, the Fan PWR circuit exceeded normal current draw. This could be due to a hard fault or an intermittent condition. Possible causes for this fault are:
   • Short to ground in Fan PWR circuit.
   • Faulty cooling fan motor.
   • Faulty VLCM.

   Clear DTCs. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1483 is present, go to next step. If Continuous Memory DTC P1483 is not present (intermittent), go to step 14).

5. 11) Check Cooling Fan Motor
   
   Clear continuous memory. Disconnect cooling fan motor connector. Start engine. Turn A/C on and wait 15 seconds (but no longer than 20 seconds). Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1483 is present, go to next step. Ignore any other DTCs at this time. If Continuous Memory DTC P1483 is not present, replace cooling fan motor.
6. 12) Check For Short To Ground In Fan PWR Circuit
   
   Turn ignition off. Ensure cooling fan motor connector is disconnected. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between Fan PWR circuit at cooling fan wiring harness connector and negative battery terminal. If resistance is more than 10,000 ohms, replace VLCM. Reconnect all components. Clear DTCs. 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, locate and repair short to ground in Light Blue wire. Clear DTCs. 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 12) to step 14). No test procedures have been omitted.
7. 14) Check For Intermittent Short To Ground In Cooling Fan Circuit
   
   Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Visually inspect Fan PWR circuit between terminal No. 2 (Light Blue wire) at VLCM connector and cooling fan motor connector. Repair wiring as necessary. Connect a non-powered test light between terminals No. 2 (Light Blue wire) and No. 4 (Dark Blue wire). Test light should be on, but not at full brightness. Observe test light for indication of fault (test light will get brighter to indicate fault) while performing the following:
   • Shake, wiggle and bend Fan PWR circuit (Light Blue wire) near cooling fan motor.

   Disconnect cooling fan motor connector. Test light should now be off. Again, observe test light for indication of fault (test light will turn on to indicate fault) while performing the following:

   • Shake, wiggle and bend Fan PWR circuit (Light Blue wire) between VLCM and cooling fan motor connector.

   If a fault is indicated, isolate fault and repair as necessary. Reconnect all components. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST . If no fault is indicated, problem is intermittent and cannot be duplicated at this time. Go to CIRCUIT TEST Z .

   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 14) to step 20). No test procedures have been omitted.
8. 20) DTC P1473: Verify Cooling Fan Is Not Always On
   
   Key On Engine Off (KOEO) DTC P1473 indicates an open or short to power in Fan PWR circuit. Possible causes for this fault are:
   • Open or short to power in Fan PWR circuit.
   • Open cooling fan motor ground circuit.
   • Open circuit in cooling fan.
   • Faulty VLCM.
   NOTE: Ensure cooling fan was not turning during KOEO ON-DEMAND SELF-TEST. If fan was turning, feedback voltage could be sent to VLCM through Fan PWR circuit, resulting in an invalid KOEO DTC P1473.

   Ensure engine is cooled off (cooling fan off). Turn A/C and defroster off. Turn ignition on. If cooling fan is on, go to step 25). If cooling fan is off, go to next step.

9. 21) Check Cooling Fan Ground Circuit
   
   Turn ignition off. Disconnect cooling fan motor connector. Measure resistance between chassis ground and cooling fan ground circuit (Black wire) at cooling fan wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, locate and repair open in cooling fan ground circuit.
10. 22) Check Fan PWR Circuit
    
    Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance of Fan PWR circuit (Light Blue wire) between cooling fan wiring harness connector and terminals No. 2 and 3 at VLCM wiring harness connector. 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 in Fan PWR circuit between VLCM and cooling fan connector.
11. 23) Check For Open Circuit In Cooling Fan Motor
    
    Measure resistance between ground circuit and Fan PWR circuit at cooling fan motor connector. If resistance is less than 10 ohms, replace VLCM. If resistance is 10 ohms or more, replace cooling fan motor.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 23) to step 25). No test procedures have been omitted.
12. 25) Check For Short To Power
    
    Turn ignition on. Measure voltage between ground and Fan PWR circuit (Light Blue wire) at cooling fan motor wiring harness connector. If voltage is less than one volt, replace VLCM. If voltage is one volt or more, locate and repair short to power in Fan PWR circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 40). No test procedures have been omitted.
13. 40) DTC P1539: Attempt To Regenerate DTC
    
    DTC P1539 indicates that when A/C was activated, the A/C Clutch PWR circuit exceeded normal current draw. This could be due to a hard fault or an intermittent condition. Possible causes for this fault are:
    • Short to ground in A/C Clutch PWR circuit.
    • Faulty A/C clutch.
    • Faulty VLCM.

    Clear DTCs. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1539 is present, go to next step. If Continuous Memory DTC P1539 is not present (intermittent), go to step 44).

14. 41) Check A/C Clutch
    
    Clear DTCs. Disconnect A/C clutch connector. Start engine. Turn A/C on and wait about 15 seconds. Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1539 is present, go to next step. Ignore any other DTCs at this time. If Continuous Memory DTC P1539 is not present, check A/C clutch external wiring for short to ground. Repair as necessary and retest. If A/C clutch wiring is okay, replace A/C clutch.
15. 42) Check For Short To Ground In A/C Clutch PWR Circuit
    
    Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance of A/C Clutch PWR circuit (Purple wire) between A/C clutch wiring harness connector and negative battery terminal. If resistance is more than 10,000 ohms, replace VLCM. Reconnect all components. Clear DTCs. 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, locate and repair short to ground in A/C Clutch PWR circuit. Clear DTCs. 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 42) to step 44). No test procedures have been omitted.
16. 44) Check For Intermittent Short To Ground In POWER-TO-A/C CLUTCH Circuit
    
    Turn ignition off. Disconnect A/C clutch connector. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Visually inspect A/C Clutch PWR circuit between terminal No. 18 at VLCM connector and A/C clutch connector. Repair wiring as necessary. Connect a non-powered test light between terminals No. 4 and 18 at VLCM wiring harness connector. Test light will turn on if fault is located, indicating a short to ground. Observe test light for indication of fault while performing the following:
    • Shake, wiggle and bend A/C Clutch PWR circuit between VLCM wiring harness connector and A/C clutch.

    If a fault is indicated, isolate fault and repair as necessary. Reconnect all components. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Repeat QUICK TEST . If no fault is indicated, problem is intermittent and cannot be duplicated at this time. Go to CIRCUIT TEST Z .

    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.
17. 50) DTC P1530: Attempt To Regenerate DTC
    
    DTC P1530 indicates an open or short to power in A/C Clutch PWR circuit. Possible causes for this fault are:
    • Open or short to power in A/C Clutch PWR circuit.
    • Open A/C clutch ground circuit.
    • Open circuit in A/C clutch.
    • Faulty VLCM.

    Clear DTCs. Start engine. Turn A/C on and wait 15 seconds. Turn A/C and ignition off. Check for continuous memory DTCs. If Continuous Memory DTC P1530 is present, go to next step. If Continuous Memory DTC P1530 is not present (intermittent), go to step 55).

18. 51) Check For Short To Power
    
    Turn ignition off. Disconnect A/C clutch connector. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. Measure voltage between chassis ground and A/C Clutch PWR circuit (Purple wire) at A/C clutch wiring harness connector. If voltage is less than one volt, go to next step. If voltage is one volt or more, locate and repair short to power in A/C Clutch PWR circuit. Reconnect all components. Clear DTCs. Turn A/C off. Start engine and wait 15 seconds. Turn ignition off. Repeat QUICK TEST .
19. 52) Check For Open Circuit
    
    Turn ignition off. Measure resistance between A/C Clutch PWR circuit at A/C clutch wiring harness connector and terminal No. 18 at VLCM wiring harness connector. Also, measure resistance between chassis ground and A/C clutch ground circuit (Black wire) at A/C clutch wiring harness connector. 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. Clear DTCs memory. Turn A/C off. Start engine and wait 15 seconds. Turn ignition off. Reconnect all components and repeat QUICK TEST .
20. 53) Check Resistance Of A/C Clutch
    
    Measure resistance between A/C clutch terminals. If resistance is less than 10 ohms, replace VLCM. Clear DTCs. Turn A/C off. Start engine and wait 15 seconds. Turn ignition off. Reconnect all components and repeat QUICK TEST . If resistance is 10 ohms or more, replace A/C clutch. Clear DTCs. Turn A/C off. Start engine and wait 15 seconds. Turn ignition off. Reconnect all components and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 53) to step 55). No test procedures have been omitted.
21. 55) Check For Intermittent Short To B+ In A/C Clutch PWR Circuit
    
    Turn ignition off. Turn A/C off. Visually inspect A/C Clutch PWR circuit between VLCM connector and A/C clutch connector. Also, check A/C clutch ground circuit. Repair wiring as necessary. If wiring is okay, turn ignition on. Observe A/C clutch for indication of fault while performing the following:
    • Shake, wiggle and bend A/C Clutch PWR circuit between VLCM connector and A/C clutch connector.

    If a fault is indicated, A/C clutch will engage indicating a short to power exists. If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, go to next step.

22. 56) Check For Intermittent Open Circuit
    
    Turn ignition off. Disconnect A/C clutch connector. Disconnect and inspect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Connect a non-powered test light between A/C clutch terminals. Connect a jumper wire between battery positive terminal and terminal No. 18 at VLCM wiring harness connector. Ensure jumper wire does not contact any other VLCM terminals. Test light should be on. Observe test light for indication of fault (test light will turn off) while performing the following:
    • Shake, wiggle and bend A/C Clutch PWR circuit and ground circuit.

    If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, problem is due to an intermittent condition and cannot be duplicated at this time. Go to CIRCUIT TEST Z .

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 56) to step 60). No test procedures have been omitted.
23. 60) KOEO/KOER DTC P1625 &/Or DTC P1626
    
    DTC P1625 indicates that B+ to VLCM fan circuit is not detected. DTC P1626 indicates that B+ to VLCM A/C circuit is not detected. Testing for both DTCs is the same. Possible causes for this fault are:
    • Open B+ circuit to VLCM terminals No. 4 and 5.
    • Faulty VLCM.

    Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure voltage between terminals No. 4 and No. 5 at VLCM wiring harness connector and negative battery terminal. If both voltage readings are more than 10.5 volts, replace VLCM. If any voltage reading is 10.5 volts or less, check A/C clutch related fuses. If fuses are okay, locate and repair open in B+ circuit. If fuses are blown, check for short to ground in B+ circuit. Repair as necessary.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 60) to step 65). No test procedures have been omitted.
24. 65) Continuous Memory DTC P1625 &/Or DTC P1626
    
    Continuous Memory DTC P1625 indicates that an open B (+) supply to VLCM fan circuit has been detected. Continuous Memory DTC P1626 indicates that an open B+ supply to VLCM A/C circuit has been detected. Testing for both DTCs is the same. Possible cause for this fault is:
    • Intermittent open B+ circuit to VLCM terminals No. 4 and 5.

    Turn ignition off. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Connect a non-powered test light between ground and terminal No. 5 at VLCM wiring harness connector. 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, wiggle and bend B+ circuit (Dark Blue wire) to terminals No. 4 and 5 at VLCM connector.
    • Lightly tap on cooling fan related fuses.

    Remove cooling fan related fuses and check for corrosion and damaged pins. Reinstall fuses. If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, problem is intermittent and cannot be duplicated at this time.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 65) to step 75). No test procedures have been omitted.
25. 75) DTC 1464: Check ACCS PID
    
    Turn ignition off. Ensure A/C and defroster are off. Turn ignition on. Using scan tool, select ACCS PID from PID/DATA monitor menu. If PID value indicates ON, PCM is receiving a request from Electronic Automatic Temperature Control (EATC) module, to turn A/C on. This request is coming from BUS+ and BUS- circuits. Diagnose A/C system. See A/C-HEATER SYSTEM article. If PID value indicates OFF, no problem is indicated at this time. DTC may have set because A/C and defrost switch were on during self-test. Repeat QUICK TEST  with A/C, defrost switch and all accessories off.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 77) to step 80). No test procedures have been omitted.
26. 80) DTC U1021 Or U1073
    
    These DTCs indicate a failure in BUS communications circuits between PCM and VLCM. If any other DTCs are present, service DTCs before continuing with this test. If no other DTCs are present, go to next step.
27. 81) DTC Identification
    
    If DTC U1021 Or U1073 is present in KOEO ON-DEMAND SELF-TEST  or KOER ON-DEMAND SELF-TEST, a fault is not present but PCM is able to communicate with scan tool. BUS circuits to Data Link Connector (DLC) are okay. Go to next step. If DTC U1021 Or U1073 is present in Continuous Memory, go to step 87).
28. 82) Check BUS+ & BUS- Circuit Resistance
    
    Turn ignition off. Disconnect scan tool from DLC. Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 15 at breakout box and terminal No. 23 (BUS-) at VLCM wiring harness connector. Also, measure resistance between test pin No. 16 at breakout box and terminal No. 21 (BUS+) at VLCM wiring harness connector. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open in appropriate BUS circuit.
29. 83) Check BUS+ & BUS- Circuit For Short To Power
    
    Turn ignition on. Measure voltage between negative battery terminal and test pin No. 15 (BUS-) at breakout box. Also, measure voltage between negative battery terminal and test pin No. 16 (BUS+) at breakout box. If both voltage readings are less than 8 volts, go to next step. If any voltage reading is 8 volts or more, repair short to power in appropriate BUS circuit.
30. 84) Check BUS+ & BUS- Circuit Integrity
    
    Turn ignition off. Measure resistance between negative battery terminal and test pins No. 15(BUS-) and 16 (BUS+) at breakout box. Also, measure resistance between test pins No. 15 and 16 at breakout box. If any resistance reading is 500 ohms or less, repair short to ground in appropriate BUS circuit. If all resistance readings are more than 500 ohms, ensure battery is fully charged and BUS circuit wiring harness is not misrouted by any high current/voltage circuits (secondary ignition wires, cellular phone or C.B. radio antennas). Repair as necessary and repeat KOEO ON-DEMAND SELF-TEST  and KOER ON-DEMAND SELF-TEST. If no faults are found, replace VLCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 84) to step 87). No test procedures have been omitted.
31. 87) System Inspection
    
    Check BUS+ and BUS- wiring harness for proper routing away from other high current circuits (secondary ignition wires, cellular phone or C.B. radio antennas). Repair as necessary. If vehicle is operated or attempted to be started with a low or dead battery, "U" DTCs can be set. Check if this has occurred (if possible). If an off-board diagnostic tool, such as Service Bay Diagnostic System (SBDS) was being used to control PCM, and the function was suddenly stopped (example; tool unplugged) without a normal exit, "U" DTCs can be set. Check if this has occurred (if possible). If no faults are found, go to next step.
32. 88) Check BUS+ & BUS- Circuit For Intermittent Short To Power
    
    Turn ignition off. Disconnect scan tool from Data Link Connector (DLC). Disconnect VLCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Connect a jumper wire between terminals No. 21 (BUS+) and 23 (BUS-) at VLCM wiring harness connector. Set DVOM on DC voltage scale. Connect DVOM between test pins No. 15 (BUS-) and No. 77 (PWR GND) at breakout box. Turn ignition on. Observe DVOM for indication of fault (voltage will suddenly increase to indicate fault) while performing the following:
    • Shake, wiggle and bend BUS+ and BUS- circuits between PCM and VLCM wiring harness connectors.

    If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, go to next step.

33. 89) Check BUS+ & BUS- Circuit For Intermittent Open Circuit
    
    Turn ignition off. Leave jumper wire connected between terminals No. 21 and 23 at VLCM wiring harness connector. Connect ohmmeter between test pins No. 15 and No. 16 at breakout box. Resistance should be 5 ohms or less. Observe ohmmeter for indication of fault (resistance will suddenly increase to indicate fault) while performing the following:
    • Shake, wiggle and bend BUS+ and BUS- circuits between PCM and VLCM harness connectors.

    If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, go to next step.

34. 90) Check BUS+ & BUS- Circuits For Intermittent Short To Power
    
    Leave jumper wire connected between terminals No. 21 and 23 at VLCM wiring harness connector. Connect ohmmeter between test pins No. 15 (BUS-) and No. 77 (PWR GND) at breakout box. Ohmmeter should indicate a stable resistance. Observe ohmmeter for indication of fault (resistance will suddenly drop to indicate short circuit) while performing the following:
    • Shake, wiggle and bend BUS+ and BUS- circuits between DLC, PCM and VLCM connectors.

    Remove jumper wire from VLCM wiring harness connector. Connect ohmmeter between test pins No. 15 and No. 16 at breakout box. Ohmmeter should indicate a stable resistance. Observe ohmmeter for indication of fault while performing the following:

    • Shake, wiggle and bend BUS+ and BUS- circuits between DLC, PCM and VLCM connectors.

    If a fault is indicated, isolate fault and repair as necessary. If no fault is indicated, problem is intermittent and cannot be duplicated at this time. Testing is complete.