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. 5V?


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 16.


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 17.


12.Turn the ignition switch OFF.

13.Disconnect the negative cable from the battery.

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

15.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 - Substitute a known-good ECM/PCM and recheck. If prescribed voltage is now available, replace the original  ECM/ PCM. If not, check the A/C system for other symptoms.n


16.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

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

 

Is there less than 1.0 V?


YES - Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original  ECM/ PCM. If not, inspect the air conditioning system.n


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