State emissions tests need to be done, but when a vehicle does not pass the test the first time, where do you look? This Real Fix provides multiple diagnostic procedures that could lead you to the fault. Kiss that ugly engine coolant temperature sensor wiring harness damage goodbye and ensure that the Saturn passes the emissions test with flying colors.
Vehicle
2001 Saturn SC2, 1.9L
Complaint
The customer states the vehicle fails emissions tests.
Cause
Connected a five gas analyzer probe to the tail pipe, ran the engine and found the hydrocarbon and carbon monoxide readings were excessive. Performed a visual inspection of the ignition system and found no obvious faults. Connected a fuel pressure gauge to the fuel pressure test port and found the measured fuel pressure was within the specified range of 40-55 psi. Used a scan tool to monitor live data and found the fuel trim parameter read -20%, which indicated the engine was running rich. At idle, used the scan tool to monitor live data and found the engine coolant temperature sensor signal parameter read 10 degrees Fahrenheit. Used an infrared thermometer to measure the engine coolant temperature at the engine coolant thermostat housing and found the actual engine temperature was 195 degrees Fahrenheit. The cold temperature reading caused the engine to run rich. Visually inspected the engine coolant temperature sensor wiring harness and found the harness was damaged.
Correction
Repaired the engine coolant temperature sensor wiring harness and verified the vehicle operated properly. The customer’s concern did not return.
Courtesy of Mitchell1 SureTrack Real Fix