A/C Signal Circuit Troubleshooting
A/C Signal Circuit Troubleshooting1. 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 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.
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 the ECM (A27) and the A/C pressure switch.
NO - Update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM.
15. Momentarily connect under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.
NOTE: The under-hood fuse/relay box 16P connector is on the bottom of the fuse box. When you unbolt and invert the fuse box, leave the upper cover on 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 terminal A27 and B20.
Is there less than 1.0 V?
YES - Update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM.
NO - Repair open in the wire between the ECM (A 27) and the A/C pressure switch, or an open between the A/C pressure switch and the heater control panel.