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A/C Signal Circuit Troubleshooting

  1. Turn the ignition switch OFF.
  2. Disconnect the A/C pressure switch connector.
  3. Turn the ignition switch ON (II).
  4. Measure voltage between ECM/PCM connector terminals A27 and B20.
    Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals A27 & B20
    G02557370Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there approx. 5V? 

    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 connector.
  7. Turn the ignition switch ON (II).
  8. Momentarily connect ECM/PCM connector terminals A17 and B20 with a jumper wire several times.
    Fig 2: Connecting ECM/PCM Connector Terminals A17 & B20 With Jumper Wire
    G02557371Courtesy 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 ECM/PCM connector A (32P)
  14. Check for continuity between body ground and ECM/PCM connector terminal A27.
    Fig 3: Checking Continuity Between Body Ground & ECM/PCM Connector Terminal A27
    G02557372Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  - Repair short in the wire between the ECM/PCM (A27) and the A/C pressure switch.
    2. NO  - Substitute a known-good ECM/PCM and recheck (see HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES ). If the prescribed voltage is now available, replace the original ECM/PCM. If not, check the A/C system for other symptoms.
    15. NOTE: The under-hood fuse/relay box 16P connector is on the bottom of the fuse box. When you unbolt and invert the fuse box, leave the upper cover on to prevent short circuits.
    Fig 4: Connecting Under-Hood Fuse/Relay Box 16P Connector Terminal No. 11 To Body Ground With Jumper Wire
    G02557373Courtesy of AMERICAN HONDA MOTOR CO., INC.
  15. Momentarily connect under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.

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

    1. YES  - Repair open in the wire between the ECM/PCM (A17) and the A/C clutch relay.
    2. NO  - Check the A/C system for other symptoms.
  16. Measure voltage between ECM/PCM connector terminals A27 and B20.
    Fig 5: Measuring Voltage Between ECM/PCM Connector Terminals A27 & B20
    G02557374Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there less than 1.0 V? 

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