Diagnostic Aids

Perform this test when directed by QUICK TEST. This CIRCUIT TEST is intended to diagnose:

• Wiring harness circuits (ECT and SIGRTN).

Fig 1: ECT Circuit & Connector Terminal ID (ECT1)

1) Check PCM Input Signal  A scan tester with ECT output signal reading capability is required for step 1). If scan tester is not available, go to next step. Turn ignition off. Connect scan tester. Start engine. Observe signal as engine warms to operating temperature. If ECT output signal value gradually increases to 158°F (70°C), system is operating correctly. If ECT related driveability problems are still present, replace PCM. If ECT output signal value does not gradually increase to 158°F (70°C), go to next step.

2) Check ECT Voltage  Turn ignition off. Disconnect ECT sensor wiring harness connector. Turn ignition on. Measure voltage between sensor wiring harness connector ECT terminal and ground. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 4).

3) Check ECT Sensor Resistance  Allow engine to cool. Start engine. Use a thermometer to monitor engine coolant temperature. Warm engine to temperature specifications shown in ECT SENSOR RESISTANCE SPECIFICATIONS table. Turn ignition off. Disconnect ECT sensor wiring harness connector. Measure resistance between connector terminals. If resistance is correct, replace PCM. If resistance is not correct, replace ECT sensor.

4) Check SIGRTN Circuit  Turn ignition off. Install Breakout Box(007-00033), leaving PCM disconnected. Disconnect ECT sensor wiring harness connector. Measure resistance between breakout box test pin No. 46 and SIGRTN terminal of ECT sensor wiring harness connector. If resistance is 5 ohms or less, repair SIGRTN circuit between ECT sensor and PCM. If resistance is more than 5 ohms, repair ECT circuit between ECT sensor and PCM.