Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
A/C Signal Circuit Troubleshooting
- Start the engine, and let it idle.
- Turn the blower switch on.
- Turn the A/C switch on.
- Check the A/C CLUTCH in the DATA LIST with the HDS.
Does it indicate ON?
YES - Go to step 5.
NO - Go to step 14.
- Check the A/C system.
Does the A/C system operate?
YES - The air conditioning system circuit is OK.
NO - Go to step 6.
- Turn the ignition switch OFF.
- Turn the ignition switch ON (II).
- Activate the A/C CLUTCH in the INSPECTION MENU with the HDS.
Is there a clicking noise from the A/C compressor clutch?
YES - Do the A/C system test (see A/C SYSTEM TEST ).
NO - Go to step 9.
- Turn the ignition switch OFF.
- Jump the SCS line with the HDS.
- Disconnect ECM/PCM connector E (31P).
- Turn the ignition switch ON (II).
- Momentarily connect ECM/PCM connector terminal E18 to body ground with a jumper wire several times.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there a clicking noise from the A/C compressor clutch?
YES - Update the ECM/PCM if it does not have the latest software (see UPDATING THE ECM/PCM ), or substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ), then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM (see ECM/PCM REPLACEMENT ).
NO - Check for poor connections or loose terminals at the A/C clutch relay and the ECM/PCM. If the connections and terminals are OK, check the A/C clutch relay (see POWER RELAY TEST ), also repair open in the wire between the ECM/PCM (E18) and the A/C clutch relay and the other A/C systems.
- Turn the ignition switch OFF.
- Disconnect the A/C pressure switch 2P connector.
- Turn the ignition switch ON (II).
- Measure voltage between ECM/PCM connector terminals A9 and E28.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there about 5 V?
YES -
- Repair open in the wire between the ECM/PCM (E28) and the A/C pressure switch.
- Go to the A/C pressure switch circuit troubleshooting (see A/C PRESSURE SWITCH CIRCUIT TROUBLESHOOTING ).
NO - Go to step 18.
- Turn the ignition switch OFF.
- Jump the SCS line with the HDS.
- Disconnect ECM/PCM connector E (31P).
- Check for continuity between ECM/PCM connector terminal E28 and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES - Repair short in the wire between the ECM/PCM (E28) and the A/C pressure switch.
NO - Update the ECM/PCM if it does not have the latest software (see UPDATING THE ECM/PCM ), or substitute a known-good ECM/PCM, then recheck (see SUBSTITUTING THE ECM/PCM ). If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM (see ECM/PCM REPLACEMENT ).
Use the Manual With the Right Hardware
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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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