P0116 Engine Coolant Temperature Sensor 1 Circuit Range/Performance
The engine coolant temperature sensor 1 is an NTC thermistor: the control module feeds 5 V through a resistor, and as the coolant warms the resistance and signal voltage fall. Its value drives cold-start enrichment, idle speed, ignition timing, the radiator fan and the release of closed-loop mixture control. Some Ford engines measure cylinder head temperature instead and calculate a coolant value from it. P0116 is a plausibility fault: the signal is electrically valid but not believable. Most often it checks for a sensor stuck too warm. After a long soak (GM 8 h, Ford 6 h) coolant must be close to intake air temperature; GM fails it above about 19 °C difference without a detected block heater, Ford if it reads over 110 °C or sits at 79–110 °C. Ford diesels instead check whether coolant warms fast enough in frost. A sensor stuck warm suppresses cold-start enrichment and can defeat the thermostat monitor, which is why CARB requires this test. GM uses one or two trips depending on the engine.
Likely causes
Symptoms
- Check engine light on
- Poor cold start (too little enrichment)
- Higher consumption or idle problems
- Often no noticeable symptoms
Repair estimate
Typical range across vehicles; the real cost depends on what the testing finds.
What to check first
- Watch warm-up curve on a scan tool
- Check thermostat operation
- Check coolant level
Parts involved
Related codes
References: law.cornell.edu, gsi.ext.gm.com, fordservicecontent.com, fordservicecontent.com.