OBD-II Code P0116 — What It Means & How to Fix It

What Does This Error Mean?

P0116 means the coolant temperature sensor is giving readings that don't make sense for current conditions. The sensor is working — it just isn't reading correctly. For example, the sensor might show a cold reading even after the engine has been running for 20 minutes. Common causes are a failing coolant temperature sensor, air pockets in the cooling system, or a stuck-open thermostat. Symptoms may include rough idle, poor fuel economy, or the engine running too long before the heater blows warm air.

Affected Models

All vehicles 1996+
Common in GM vehicles (3.8L, 3.6L)
Common in Ford Focus
Common in Toyota 4Runner
Common in Nissan Sentra

Common Causes

Failing engine coolant temperature (ECT) sensor with a drifting or lazy resistance curve
Air pockets in the cooling system causing inconsistent coolant flow past the sensor
Stuck-open thermostat preventing the engine from reaching normal operating temperature
Corroded or damaged sensor connector causing intermittent resistance readings
Coolant leak that has lowered the coolant level, leaving the sensor partially exposed to air

How to Fix It

Check the coolant level in the overflow reservoir. A low coolant level can leave the ECT sensor surrounded by air instead of liquid, causing erratic temperature readings. Top off with the correct coolant type if low.

Check for coolant leaks if the level is significantly low. Look under the car for puddles, check hose connections, and inspect the radiator for staining. A leaking system should be pressure-tested.
Check your temperature gauge behavior. After a cold start, the gauge should rise smoothly and settle in the middle within 5-10 minutes of driving. If it stays low or never moves, the thermostat is likely stuck open.

A stuck-open thermostat is a very common cause of P0116. It is inexpensive to replace — usually $15-$40 for the part — and should be done as part of a cooling system service.
Locate the coolant temperature sensor. It is typically threaded into the engine block or cylinder head near where the upper radiator hose connects. It has one or two wires. Unplug it and inspect the connector for green corrosion or bent terminals.

Clean corroded contacts with fine sandpaper or electrical contact cleaner. Reconnect firmly and clear the code to see if it returns before replacing the sensor.
Test the sensor resistance with a multimeter. On a cold engine, the sensor should read high resistance (1,500-3,000 ohms on many vehicles). As the engine warms, resistance should drop smoothly. Erratic or wrong readings confirm a bad sensor.

You can find the exact resistance chart for your vehicle in a service manual or on AllDataDIY. The resistance curve must be smooth and consistent — jumpy readings mean the sensor is failing.
Replace the sensor if it fails the resistance test. Drain a small amount of coolant first to prevent a spill. Install the new sensor, refill coolant if needed, and bleed any air from the cooling system. Clear the code and verify the repair.

Bleeding air from the cooling system is important. Air pockets cause erratic temperature readings. Many vehicles have a bleeder screw on the thermostat housing — consult your owner's manual.

When to Call a Professional

P0116 is usually a DIY-friendly repair. A coolant temperature sensor costs $15-$50 and is simple to replace on most engines. A stuck thermostat replacement runs $100-$300 at a shop. If the code is caused by a coolant leak, have the cooling system pressure-tested by a mechanic. Do not ignore cooling system issues — an overheating engine can cause severe and costly damage.

Frequently Asked Questions

What does range/performance mean for a sensor code?

Range/performance codes (like P0116) are different from circuit fault codes. A circuit fault means the sensor is electrically dead or has a broken wire. A range/performance code means the sensor is electrically alive but giving irrational readings. For example, the temperature never changes even as the engine warms up. Or it reads hotter than is physically possible for the current conditions.

How does P0116 affect fuel economy?

The ECM uses coolant temperature to control fuel enrichment. On a cold engine, it adds extra fuel to keep the engine running smoothly. If the sensor reports the engine is always cold, the ECM keeps adding extra fuel — wasting gas. You might notice 10-20% worse fuel economy while this code is active. Fixing the sensor usually restores normal fuel consumption right away.

Can I drive with P0116?

Yes, usually for short periods. The engine will still run, but it may use more fuel than normal. Watch the temperature gauge closely while driving. If the gauge climbs into the red or shows unusual behavior, pull over immediately. A cooling system problem that leads to overheating can destroy an engine quickly.