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Electrical/Accessory Load Idle-Up Circuit Diagnosis: Notes

  1. If powertrain diagnostic system check has been performed, go to next step. If powertrain diagnostic system check has been performed, perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
    2. NOTE: If headlights, HVAC blower motor, or rear defogger do not operate properly, diagnose those components first.
  2. Start and warm engine to normal operating temperature. Turn off all accessories. Using scan tool, monitor engine RPM and IAC duty cycle while turning each of the following accessories on and off:
    • Headlights
    • HVAC blower motor
    • Rear window defogger
    If scan tool indicates increase in IAC duty cycle when each accessory is turned on, go to next step. If scan tool does not indicate increase in IAC duty cycle when each accessory is turned on, go to step  20.
  3. Turn all accessories off. Turn A/C switch to ON position and blower speed selector switch to any position except OFF. Using scan tool, monitor engine RPM and the IAC duty cycle while operating A/C system. If IAC duty cycle increases when A/C compressor in operating, go to next step. If IAC duty cycle does not increase when A/C compressor in operating, go to step 10.
  4. Turn all accessories off. Using scan tool, monitor engine RPM and IAC duty cycle while turning steering wheel fully right and left. If IAC duty cycle increases when turning steering wheel fully right and left, see appropriate TROUBLE SHOOTING - NO CODES article. If IAC duty cycle does not increase, go to next step.
  5. Turn all accessories off. Using scan tool, monitor power steering switch. Turn steering wheel fully right and left. If scan tool indicates high pressure when steering wheel was turned fully in either direction, see IDLE AIR CONTROL SYSTEM DIAGNOSIS . If high pressure is not indicated when steering wheel was turned fully in either direction, go to next step.
  6. Turn ignition on, engine off. Disconnect Power Steering Pump (PSP) switch connector. Using DVOM, measure voltage from PSP switch connector (harness side) to ground. See WIRING DIAGRAMS article. If about battery voltage exists, go to next step. If about battery voltage does not exist, go to step  8.
  7. Connect a test light to battery voltage. Probe PSP switch connector (switch side) with test light. Start engine. Observe test light while turning steering wheel fully to right and left. If test light illuminates when steering wheel was turned fully in either direction, go to DIAGNOSTIC AIDS . If test light does not illuminate when steering wheel was turned fully in either direction, go to step  9.
  8. Check for open or short to ground in PSP circuit between PCM connector C2 terminal No. 7 (Blue/Orange wire) on 2.0L or PCM connector C1 terminal No. 26 (Blue/Orange wire) on 2.5L and PSP switch. Repair as necessary. After repairs, go to step  30. If circuit is okay, go to step  29.
  9. Check for poor ground connection at power steering pump. Repair as necessary. After repairs, go to step  30. If circuit is okay, go to step  28.
  10. Using scan tool, monitor A/C relay command. Turn A/C switch to ON position and blower speed selector switch to any position except OFF. If scan tool indicates ON when A/C compressor is operating, see IDLE AIR CONTROL SYSTEM DIAGNOSIS . If scan tool does not indicate ON when A/C compressor is operating, go to next step.
  11. Start engine. Turn A/C on. Using DVOM connected to ground, backprobe A/C ON circuit at PCM connector C1 terminal No. 17 (Yellow/Black wire) on 2.0L or PCM connector C2 terminal No. 27 (Yellow/Black wire) on 2.5L. If voltage is zero, go to next step. If voltage is not zero, go to step  14.
  12. Start engine. Turn A/C off. Using DVOM connected to ground, backprobe A/C idle-up circuit at PCM connector C1 terminal No. 17 (Yellow/Black wire) on 2.0L or PCM connector C2 terminal No. 27 (Yellow/Black wire) on 2.5L. If battery voltage exists on 2.0L or 4.5-5.0 volts exists on 2.5L, go to step  15. If voltage is not as specified, go to next step.
  13. Turn ignition off. Disconnect PCM connector C1. Back out terminal No. 17 (Yellow/Black wire) on 2.0L or terminal No. 27 (Yellow/Black wire) on 2.5L (A/C idle-up signal wire) from PCM connector. Reconnect PCM connector C1. Turn ignition on, engine off. Using DVOM connected to ground, backprobe through PCM connector slot to PCM terminal to ground. Measure voltage. If battery voltage exists on 2.0L or 4.5-5.0 volts exists on 2.5L, go to next step. If voltage is not as specified, go to step  29.
  14. Check for open or a short in A/C idle up circuit between PCM and A/C compressor control module. Repair as necessary. After repairs, go to step  30. If circuit is okay, go to step  19.
  15. Start engine. Turn A/C off. Using DVOM connected to ground, backprobe A/C cut-out circuit at PCM connector C1 terminal No. 8 (Gray/White wire) on 2.0L or PCM connector C1 terminal No. 28 (Gray/White wire) on 2.5L. If voltage does not exist, go to next step. If voltage exists, go to step  29.
  16. Start engine. Turn A/C on (A/C operating). Using DVOM connected to ground, backprobe A/C cut-out circuit at PCM connector C1 terminal No. 8 (Gray/White wire) on 2.0L or PCM connector C1 terminal No. 28 (Gray/White wire) on 2.5L. If battery voltage exists, go to DIAGNOSTIC AIDS . If battery voltage does not exist, go to next step.
  17. Check for open or short to ground in A/C cut-out circuit between PCM and A/C compressor control module. Repair as necessary. After repairs, go to step  30. If circuit is okay, go to next step.
  18. Disconnect A/C compressor control module connector. Turn ignition on, engine off. Using DVOM, measure voltage at A/C compressor control module connector terminal No. 5 and ground. If battery voltage exists, go to step  29. If battery voltage does not exist, go to next step.
  19. A/C compressor control module is malfunctioning. Inspect A/C compressor control module and circuits for a fault. See appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. Repair as necessary. After repairs, go to step  30.
  20. If scan tool indicated an increase in IAC duty cycle when HVAC blower motor was turned on, go to step  22. If scan tool did not indicate an increase in IAC Motor Command when HVAC blower motor was turned on, go to next step.
  21. Turn ignition off. Disconnect PCM connectors. Turn ignition on, engine off. Using test light connected to battery voltage, probe harness side of HVAC Blower Idle-Up circuit PCM connector C1 terminal No. 16 (Pink/White wire) on 2.0L or PCM connector C1 terminal No. 13 (Pink/White wire) on 2.5L. Observe test light while operating HVAC blower motor switch. If test light illuminates when HVAC blower motor switch is turned to ON position, go to step  29. If test light does not illuminate when HVAC blower motor switch is turned to ON position, go to step  25.
  22. If scan tool indicated an increase in IAC duty cycle when rear window defogger switch was turned to ON position, go to next step. If scan tool did not indicate an increase in IAC duty cycle when rear window defogger switch was turned to ON position, go to step  24.
  23. Using test light connected to ground, backprobe taillight idle-up circuit at PCM connector C1 terminal No. 32 (Red/Yellow wire) on 2.0L or PCM connector C1 terminal No. 29 (Red/Yellow wire) on 2.5L. Observe test light while operating headlight switch. If test light illuminates when headlight switch is turned to ON position, go to step  29. If test light does not illuminate when headlight switch is turned to ON position, go to step  26.
  24. Using test light connected to ground, backprobe rear defogger idle-up circuit at PCM connector C1 terminal No. 15. Observe test light while operating rear defogger switch. If test light illuminates when rear defogger switch is turned to ON position, go to step  29. If test light does not illuminate when rear defogger switch is turned to ON position, go to step  27.
  25. Check for correct operation of HVAC blower circuit. See appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. Check HVAC blower idle-up signal circuit for open or short. Repair as necessary. After repairs, go to step  30. If all HVAC circuits are okay, go to step  29.
  26. Check for correct operation of exterior lighting. See EXTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT. Check for open or short in taillight idle-up circuit. Repair as necessary. After repairs, go to step  30. If all exterior light circuits are okay, go to step  29.
  27. Check for correct operation of rear defogger. Check for open or short rear defogger idle-up circuit. See appropriate REAR WINDOW DEFOGGERS article in ACCESSORIES & EQUIPMENT. Repair as necessary. After repairs, go to step  30. If all rear window defogger circuits are okay, go to step  29.
  28. Replace PSP switch. After repairs, go to step  30.
  29. Replace PCM. After repairs, go to next step.
  30. Operate vehicle within conditions under which original symptom was observed. System should operate properly. If system does not operate properly, see DIAGNOSTIC AIDS .
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