P0116 Code: Engine Coolant Temp Sensor 1 Circuit Range/Performance
The coolant temperature signal is electrically fine but doesn't behave the way the PCM expects.
At a glance
Severity: Low
- Meaning
- Engine Coolant Temp Sensor 1 Circuit Range/Performance
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $15–$400
- DIY difficulty
- Moderate
P0116 is a plausibility code, not a wiring code. The coolant temperature sensor is a thermistor, and its voltage stays inside the normal window, but the value it reports doesn't make physical sense. The PCM runs a few sanity checks: after the car has sat overnight, coolant and intake air temperature should match; after a cold start the temperature should climb at a believable rate; and it should never jump by tens of degrees in a second. When one of those checks fails, P0116 sets. In practice the sensor has usually drifted out of calibration, a thermostat stuck open keeps the temperature from rising as modeled, or an air pocket around the sensor makes the reading erratic.
Can I keep driving? Safe to drive for now, but fueling, ignition timing and fan control all depend on this reading, so expect worse gas mileage and possibly hard cold starts until it is fixed. Don't leave it for months.
How to read P0116
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 16 Specific fault
Symptoms
- Check engine light on, often after a cold start
- Coolant temperature in live data jumps around or reads far from outside temperature after sitting overnight
- Engine takes unusually long to warm up or the heater stays lukewarm
- Radiator fans run on a cold engine, or don't come on when they should
- Rough or hard starts on cold mornings
- Gas mileage noticeably worse than usual
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Coolant temperature sensor drifted out of calibration with age (reads consistently too high or too low)
- Thermostat stuck open, so the temperature never rises the way the PCM's warm-up model predicts
- Low coolant or an air pocket around the sensor tip, giving an erratic or lagging reading
- Corroded or loose terminals adding resistance in the signal or ground wire, which makes the sensor read colder
- Coolant loss on a hot engine: the PCM sees a big temperature drop between shutdown and a restart minutes later
- Wrong replacement sensor or thermostat rating, or a PCM fault
Diagnosis step by step
Compare coolant and intake air temperature after a cold soak
After the car has sat for at least eight hours, read both values with the key on before starting. They should be within about 5°F of each other and close to the outside air temperature. A coolant reading that is 20°F or more off while intake air looks right points to a skewed sensor or its wiring.
Tools: OBD-II scanner
Log the warm-up and look at the shape of the curve
Start the engine and record coolant temperature during a normal drive. A good sensor climbs smoothly to somewhere between 190 and 220°F. Sudden steps or spikes mean an intermittent sensor or connector; a smooth climb that stalls around 150 to 170°F means the thermostat isn't closing.
Tools: OBD-II scanner
Measure sensor resistance against a real temperature
Unplug the sensor and measure across its two pins while checking the actual coolant temperature with a thermometer at the thermostat housing. Typical two-wire sensors read roughly 2,000 to 3,000 ohms at 68°F, about 300 ohms at 176°F and under 200 ohms at 212°F. Compare with the table in your service data; a sensor that is consistently off by a wide margin has drifted.
Tools: Multimeter, Gloves
Check for resistance in the wiring
With the sensor plugged in and the key on, back-probe the ground wire: it should show less than 0.1 volt to battery negative. Then wiggle the harness while watching live data. Coolant that has seeped into the connector over the years corrodes the terminals and adds resistance, which shifts the reading colder.
Tools: Multimeter, OBD-II scanner
Check coolant level and bleed the system
With the engine cold, confirm the level in the reservoir and radiator. If the sensor sits high in the head or housing, even a small air pocket leaves it reading air instead of coolant. Bleed the system per the manufacturer's procedure and recheck the warm-up curve.
Tools: Flashlight
Test the thermostat if the sensor checks out
If the sensor matches the thermometer but the engine never reaches its normal temperature, the thermostat is the problem. Feel the upper radiator hose during warm-up: it should stay cool until the thermostat opens, then get hot quickly. Gradual warming from the start means the thermostat leaks.
Tools: Gloves
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace coolant temperature sensor | Yes | $60–$200 |
| Clean or replace corroded sensor connector | Yes | $20–$120 |
| Replace thermostat | Yes | $150–$400 |
| Top off coolant and bleed the system | Yes | $15–$60 |
| Repair wiring harness | No | $100–$300 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
The check engine light means an automatic fail on an OBD-II emissions test in states that use one. Coolant temperature gates most readiness monitors, so after the repair drive several full warm-up cycles before you retest or the monitors may still show not ready.
Frequently asked questions
How is P0116 different from P0117 and P0118?
P0117 and P0118 mean the signal went outside the electrical limits, which is almost always a short or an open wire. P0116 means the signal stayed inside the limits but the temperature it represents is implausible. That points to a drifted sensor, a thermostat or an air pocket rather than a broken wire.
Can a stuck thermostat set P0116 instead of P0128?
Yes. Both codes can come from the same slow warm-up; it depends on which test in that particular PCM trips first. If the sensor matches a thermometer reading, treat P0116 exactly like P0128 and test the thermostat.
The sensor measures fine on the bench. Why do I still get the code?
Because the fault may only appear hot, under vibration or with coolant in the connector. Check the resistance at operating temperature, wiggle the harness while watching live data, and confirm the coolant level. Some PCMs also flag P0116 when the temperature at a hot restart is far lower than at shutdown, which is a sign of coolant loss.
Should I just replace the sensor?
It is inexpensive and often the answer, but confirm it first by comparing the reading with a thermometer. If the sensor is accurate and the engine simply runs cold, a new sensor changes nothing and the thermostat is the real fix.