ECT Sensor Circuit Troubleshooting

Check the malfunction indicator lamp (MIL).
Does the malfunction indicator lamp come on?
1. YES - Refer to the powertrain DTCs (see GENERAL TROUBLESHOOTING INFORMATION ).
2. NO - Go to step 2.
Turn the ignition switch OFF.
Disconnect the ECT sensor 2P connector.
Disconnect the climate control unit 30P connector.
Turn the ignition switch ON (II).
Measure the voltage between the No. 18 terminal of the climate control unit 30P connector and body ground.

Fig 1: Measuring Voltage Between Terminal Of Climate Control Unit 30P Connector And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V?
1. YES - Check for loose wires or poor connections at the climate control unit 30P connector and at the ECT sensor 2P connector. If the connections are good, substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit.
2. NO - Repair open in the wire between the climate control unit and the ECT sensor.