Sensor/System Checks
- Check the Engine Coolant Temperature (ECT) sensor for being shifted in value. Install the scan tool and compare the displayed engine coolant temperature with the intake air temperature on a cold engine. Check the resistance of the ECT sensor if the engine coolant temperature is not within 5°F of Intake Air Temperature (IAT). See TEMPERATURE VS RESISTANCE table. If the ECT sensor resistance is not within specification, see DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT LOW VOLTAGE OR DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT HIGH VOLTAGE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 4.0L AURORA article.
- Check the Mass Airflow (MAF) sensor and connections.
- Check the operation of the Idle Air Control (IAC) valve. See IDLE AIR CONTROL SYSTEM DIAGNOSIS under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.0L AURORA article.
- Using the scan tool, monitor the Throttle Position (TP) sensor voltage. The TP sensor voltage should be less than 0.9 volt with a closed throttle. If the TP sensor voltage is more than 0.9 volt, inspect the throttle body and accelerator cables for binding.
- Check for the proper operation of the Exhaust Gas Recirculation (EGR) system. See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 4.0L AURORA article.