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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 connector terminals A27 and B20.
    Fig 1: Measuring Voltage Between ECM Connector Terminals A27 And B20
    G03680970Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V? 

    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 connector terminals A17 and B20 with a jumper wire several times.
    Fig 2: Connecting ECM Connector Terminals A17 And B20 With Jumper Wire
    G03680971Courtesy 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, and wait for 10 seconds.
  13. Disconnect ECM connector A (32P).
  14. Check for continuity between body ground and ECM connector terminal A27.
    Fig 3: Checking Continuity Between Body Ground And ECM Connector Terminal A27
    G03680972Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Repair short in the wire between the ECM (A27) and the A/C pressure switch.
    2. NO  -Update the ECM if it does not have the latest software, or substitute a known-good ECM; 2000-2001 M/T models (see HOW TO TROUBLESHOOT CIRCUITS AT THE ECM ), 2002-2006 M/T models and CVT models (see ECM UPDATING AND SUBSTITUTION FOR TESTING-2002-2006 M/T MODELS AND CVT MODEL ), then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM (see ECM REPLACEMENT ).
  15. Momentarily connect under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.
    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 11 To Body Ground With Jumper Wire
    G03680973Courtesy 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 ECM (A17) and the A/C clutch relay.
    2. NO  -Check the A/C system for other symptoms.
  16. Measure voltage between ECM connector terminals A27 and B20.
    Fig 5: Measuring Voltage Between ECM Connector Terminals A27 And B20
    G03680974Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there less than 1.0 V ? 

    1. YES  -Update the ECM if it does not have the latest software, or substitute a known-good ECM; 2000-2001 M/T models (see HOW TO TROUBLESHOOT CIRCUITS AT THE ECM ), 2002-2006 M/T models and CVT model (see ECM UPDATING AND SUBSTITUTION FOR TESTING-2002-2006 M/T MODELS AND CVT MODEL ), then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM (see ECM REPLACEMENT ).
    2. NO  -Repair open in the wire between the ECM (A27) and the A/C pressure switch, or between the A/C pressure switch and the heater control panel.
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