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 A24 and E28.

 


Is there approx. 5 V?


YES - Go to 5.


NO - Go to 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 A24 and E18 with a jumper wire several times.

 

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


YES - Go to 9.


NO - Go to 15.


9.Start the engine.

10.Turn the blower switch ON.

11.Turn the A/C switch ON.

Does the A/C operate?


YES - The air conditioning signal is OK.n


NO - Go to 16.


12.Turn the ignition switch OFF.

13.Disconnect ECM/PCM connector E (31P).

14.Check for continuity between body ground and ECM/PCM connector terminal E28.

 

Is there continuity?


YES - Repair short in the wire between the ECM/PCM (E28) and the A/C pressure switch.n


NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.n


15.Momentarily connect the A/C compressor clutch relay 4P connector (into the under-hood fuse/relay box) terminal No. 3 to body ground with a jumper wire several times.

 

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


YES - Repair open in the wire between the ECM/PCM (E18) and the A/C clutch relay.n


NO - Check the A/C system for other symptoms.n

16.Measure voltage between ECM/PCM connector terminals A24 and E28.

 

Is there less than 1.0 V?


YES - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.n


NO - Repair open in the wire between the ECM/PCM (E28) and the A/C pressure switch.n