Sensor Checks
- Check the Engine Coolant Temperature (ECT) sensor using a scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 9°F (5°C) more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit or in the sensor. See TEMPERATURE VS. RESISTANCE
table.TEMPERATURE VS. RESISTANCE
°F °C Resistance - Ohms 176 80 315 158 70 435 140 60 480 122 50 810 113 45 940 104 40 1150 95 35 1360 86 30 1600 77 25 2000 68 20 2400 59 15 3000 50 10 3600 41 5 4600 32 0 5700 23 -5 7400 14 -10 9800 5 -15 12700 -4 -20 16000 - Check the Throttle Position (TP) sensor. A sticking throttle shaft or a binding throttle linkage will causes a high TP sensor voltage. Under these conditions, PCM may not control the idle. Monitor the TP sensor angle with the scan tool. The indicated angle should be approximately 9-11 percent with throttle closed.
- Inspect the Mass Air Flow (MAF) sensor operation. Run engine to normal operating temperature. Turn OFF all accessories and observe the MAF sensor at idle with a scan tool. If the MAF sensor reading is more than 3.5 g/s, see DTC P0101: MAF SENSOR PERFORMANCE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 1.8L VIBE article.
- Check the Crankshaft Position (CKP) sensor engine reference signal with a scan tool. Observe ENGINE SPEED parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed are displayed, the engine reference signal is not stable enough for the engine to start and run properly.