2004 Honda Pilot EXFACTORY OEM SERVICE PROCEDURE

A/C Signal Circuit Troubleshooting

  1. Turn the ignition switch OFF.
  2. Disconnect the A/C pressure switch 2P connector.
  3. Turn the ignition switch ON (II).
  4. Measure voltage between PCM connector terminals A27 and B20.
    Fig 1: Measuring Voltage Between PCM Connector Terminals A27 & B20
    G01464132Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V or battery voltage? 

    1. YES  -Go to step 5.
    2. NO  -Go to step  12.
  5. Turn the ignition switch OFF.
  6. Reconnect the A/C pressure switch 2P connector.
  7. Turn the ignition switch ON (II).
  8. Momentarily connect PCM connector terminals A17 and B20 with a jumper wire several times.
    Fig 2: Connecting PCM Connector Terminals A17 & B20 With A Jumper Wire
    G01464133Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there a clicking noise from the A/C compressor clutch? 

    1. YES  -Go to step 9.
    2. NO  -Go to step  15.
  9. Start the engine.
  10. Turn the blower switch ON.
  11. Turn the A/C switch ON.

    Does the A/C operate? 

    1. YES  -The air conditioning signal is OK.
    2. NO  -Go to step 16.
  12. Turn the ignition switch OFF.
  13. Disconnect PCM connector A (32P).
  14. Check for continuity between body ground and PCM connector terminal A27.
    Fig 3: Checking For Continuity Between Body Ground & PCM Connector Terminal A27
    G01464134Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Repair short in the wire between the PCM (A27) and the A/C pressure switch.
    2. NO  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If prescribed voltage is now available, replace the original PCM. If not, check the A/C system for other symptoms.
  15. Momentarily connect under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.
    Fig 4: Connecting Under-Hood Fuse/Relay Box 16P Connector Terminal No. 11 To Body Ground With A Jumper Wire
    G01464135Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there a clicking noise from the A/C compressor clutch? 

    1. YES  -Repair open in the wire between the PCM (A17) and the A/C clutch relay.
    2. NO  -Check the A/C system for other symptoms.
  16. Measure voltage between PCM connector terminals A27 and B20.
    Fig 5: Measuring Voltage Between PCM Connector Terminals A27 & B20
    G01464136Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there less than 1.0 V? 

    1. YES  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If the symptom/indication goes away, replace the original PCM. If not, inspect the air conditioning system.
    2. NO  -Repair open in the wire between the PCM (A27) and the A/C pressure switch.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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