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Home >> Honda >> 2004 >> Civic Hybrid, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Idle Control System (Hybrid) >> A/C Signal Circuit Troubleshooting
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

A/C Signal Circuit Troubleshooting

  1. Turn the ignition switch OFF.
  2. Disconnect the A/C compressor 3P connector.
  3. Turn the ignition switch ON (II).
  4. Measure voltage between ECM connector terminals A24 and E28.
    Fig 1: Measuring Voltage Between ECM Connector Terminals A24 & E28
    G01460332Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V? 

    • YES  - Go to step 5.
    • NO  - Go to step 13.

  5. Turn the ignition switch OFF.
  6. Reconnect the A/C compressor 3P connector.
  7. Turn the ignition switch ON (II).
  8. Momentarily connect ECM connector terminals A5 and E18 with a jumper wire several times.
    Fig 2: Connecting ECM Connector Terminals A5 & E18 With Jumper Wire
    G01460333Courtesy 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 17.

  9. Remove the jumper wire from the ECM connectors.
  10. Start the engine.
  11. Turn the blower switch ON.
  12. Turn the A/C switch ON.

    Does the A/C operate? 

    1. YES  - The A/C switch signal is OK.
    2. NO  - Check the A/C system.

  13. Turn the ignition switch OFF.
  14. Wait for 1 minute. If the radiator fan is running, wait for 1 minute after the radiator fan stops.
  15. Disconnect ECM connector E (31P).
  16. Check for continuity between ECM connector terminal E28 and body ground.
    Fig 3: Checking Continuity Between ECM Connector Terminal E28 & Body Ground
    G01460334Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  - Repair short in the wire between the ECM (E28) and the A/C compressor.
    2. NO  - Update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck (see ECM UPDATING AND SUBSTITUTION FOR TESTING ). If the symptom/indication goes away with a known-good ECM, replace the original ECM (see HOW TO SUBSTITUTE OR REPLACE THE ECM ).

  17. Momentarily connect under-hood fuse/relay box 14P connector terminal No. 10 to body ground with a jumper wire several times.
NOTE: The under-hood fuse/relay box 14P connector is on the bottom of the fuse box. When you unbolt and invert the fuse box, leave the upper cover on it to prevent a short circuit.
Fig 4: Connecting Under-Hood Fuse/Relay Box 14P Connector Terminal No. 10 To Body Ground With Jumper Wire
G01460335Courtesy 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 (E18) and the A/C compressor clutch relay.
  2. NO  - Check the A/C system for other symptoms.

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