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.
Is there about 5 V?
YES - Go to step 5.
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.
Is there a clicking noise from the A/C compressor clutch?
YES - Go to step 9.
NO - Go to step 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.
NO - Go to step 16.
12. Turn the ignition switch OFF.
13. Disconnect ECM connector A (32P)
14. Check for continuity between body ground and ECM connector terminal A27.
Is there continuity?
YES - Repair short in the wire between ECM (A27) and the A/C pressure switch.
NO - Substitute a known-good ECM and recheck. If voltage is now normal, replace the original ECM. If not, check the A/C system for other symptoms.
15. Momentarily connect main under-hood fuse/relay box 16P connector terminal No.11 to body ground with a jumper wire several times.
NOTE: The main 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 short circuits.
Is there a clicking noise from the A/C compressor clutch?
YES - Repair open in the wire between the ECM (A17) and the A/C clutch relay.
NO - Check the A/C system for other symptoms.
16. Measure voltage between ECM connector terminals A27 and B20.
Is there less than 1.0 V?
YES - Substitute a known-good ECM and recheck. If the symptom/indication goes away, replace the original ECM. If not, inspect the A/C system.
NO - Repair open in the wire between the ECM (A 27) and the A/C pressure switch, or between the A/C pressure switch and the heater control panel.