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A/C Idle Circuit Diagnosis

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
  2. Start and warm engine to normal operating temperature. Turn off all accessories. Using scan tool, monitor A/C parameter. Turn A/C switch on and blower speed selector switch to any position except off. If scan tool indicates ON with A/C operating, A/C idle-up system is operating properly. If scan tool does not indicate ON with A/C operating, go to next step.
  3. Using DVOM connected to ground, probe A/C idle-up signal circuit (Yellow/Black wire) at PCM harness connector C1, terminal No. 17. See appropriate wiring diagram in WIRING DIAGRAMS article. If voltage is present, go to step  6 . If voltage is not present, go to next step.
  4. Turn A/C off. Using DVOM connected to ground, probe A/C idle-up signal circuit (Yellow/Black wire) at PCM harness connector C1, terminal No. 17. See appropriate wiring diagram in WIRING DIAGRAMS article. If battery voltage exists, go to step  7 . If battery voltage does not exist, go to next step.
  5. Turn ignition off. Disconnect PCM connector C1. Back out A/C idle-up signal circuit (Yellow/Black wire) from PCM connector. Reconnect PCM harness connector. Turn ignition on, engine off. Using DVOM connected to ground, backprobe through PCM connector slot to PCM terminal. If battery voltage exists, go to next step. If battery voltage does not exist, go to step  12 .
  6. Check for open or short in A/C idle-up signal circuit between PCM and A/C compressor control module. If problem exists, repair as necessary and go to step  13 . If problem does not exist, go to step  11 .
  7. Start engine. Turn A/C off. Using DVOM connected to ground, backprobe A/C cut-out control circuit (Gray/White wire) at PCM connector C1, terminal No. 8. See appropriate wiring diagram in WIRING DIAGRAMS article. If voltage exists, go to step  12 . If voltage does not exist, go to next step.
  8. Turn A/C on. Using DVOM connected to ground, backprobe A/C cut-out control circuit (Gray/White wire) at PCM connector C1, terminal No. 8. See appropriate wiring diagram in WIRING DIAGRAMS article. If battery voltage does not exist, go to next step. If battery voltage exists, check for a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect PCM harness connector for backed-out terminals, improper mating, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
  9. Check for open or short to ground in A/C cut-out control circuit between PCM and A/C compressor control module. If problem exists, repair as necessary and go to step  13 . If problem does not exist, go to next step.
  10. Disconnect A/C compressor control module connector. Turn ignition on, engine off. Using DVOM, measure voltage of A/C cut-out signal circuit (Green/Yellow wire) at A/C compressor control module connector. If battery voltage exists, go to step  12 . If battery voltage does not exist, go to next step.
  11. A/C compressor control module is malfunctioning. Check for faulty A/C compressor control module and/or circuitry. Repair as necessary. After repairs, go to step  13 .
  12. Replace PCM. After repairs, go to next step.
  13. Operate vehicle within conditions under which original symptom was observed. System should operate properly. If system does not operate properly, check for a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect PCM harness connector for backed-out terminals, improper mating, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
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