P0115: Engine coolant temperature circuit malfunction
The engine computer gets no usable signal from the coolant temperature sensor, or the signal drops out, so it uses a substitute value. On many cars the cooling fan then runs all the time; on others the gauge or the fan may not follow the real temperature.
Updated
What P0115 means
The coolant temperature sensor tells the engine computer how warm the engine is. It uses this for the fuel mixture and idle speed when cold, and on many cars to switch the cooling fan and drive the temperature gauge. Some engines have a separate sensor for the gauge.
The sensor’s resistance changes with temperature, and the engine computer reads it as a voltage. P0115 means it has found a fault in that circuit; it then uses a substitute value.
Read My Car shows the coolant temperature under Live data. On a cold engine that has stood for hours, it should be close to the outside temperature.
P0116 to P0119: implausible, low, high or intermittent
P0117 (low) reads as an implausibly hot engine and usually means a short circuit. P0118 (high) reads as an implausibly cold engine and usually means a broken connection or an unplugged sensor. P0116 means the reading is there but doesn’t fit, for example it rises too slowly as the engine warms up, and P0119 means it drops out. The urgency is the same for all of them.
P0116: Engine coolant temperature circuit range/performance
The coolant temperature sensor’s reading doesn’t fit what the engine computer expects: for example it rises too slowly as the engine warms up, or jumps. The engine computer may use a substitute value.
Common causes: faulty coolant temperature sensor, thermostat stuck open, low coolant level or air in the cooling system, wiring or connector fault.
P0117: Engine coolant temperature circuit low input
The coolant temperature sensor’s signal is at the bottom of its range, so the engine computer reads an implausibly hot engine. This usually points to a short circuit. The engine computer uses a substitute value, and on many cars runs the cooling fan all the time.
Common causes: faulty coolant temperature sensor, signal wire shorted to earth, or a damaged connector, fault in the engine computer (rare).
P0118: Engine coolant temperature circuit high input
The coolant temperature sensor’s signal is at the top of its range, so the engine computer reads an implausibly cold engine. This usually points to a broken connection. The engine computer uses a substitute value, and the gauge may stay at cold.
Common causes: sensor unplugged, or a loose or corroded connector, broken wire in the sensor circuit, faulty coolant temperature sensor.
P0119: Engine Coolant Temperature Sensor 1 Circuit Intermittent/Erratic
Can I keep driving?
Drive gently
Drive gently and only as far as you need to, and have it checked soon. With a wrong coolant temperature reading, the temperature gauge and warning light may not show overheating, and the cooling fan may not switch on when it’s needed, so the engine can overheat without warning. Check the coolant level when the engine is cold. If you see steam, smell hot coolant, the heater suddenly blows cold or a temperature warning comes on, stop when it’s safe to do so and switch the engine off.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
What the car does with a substitute value differs. Many cars run the cooling fan all the time, but on others the gauge or the fan may not follow the real temperature. Until it’s fixed, don’t rely on the temperature gauge alone.
Don’t count on an overheating code (P0217) or the temperature warning to tell you: on most cars they rely on this same sensor. Watch for steam, a smell of hot coolant or the heater suddenly blowing cold, and if you notice any of them, stop when it’s safe to do so and switch the engine off.
Symptoms
- The cooling fan running all the time, even on a cold engine.
- The temperature gauge reading wrong, or not moving.
- Hard starting, a rough idle or higher fuel use, mostly when cold.
- On some cars, the air conditioning not working.
Common causes
- Wiring or connector fault. The connector sits on the hot engine: check it for corrosion, coolant in the plug and damaged wires.
- Faulty coolant temperature sensor. Replace it only after the plug and wiring check out, and only with the engine cold.
- Low coolant level. A sensor that isn’t surrounded by coolant reads wrong. Check the level with the engine cold, and look for leaks if it’s low.
Typical fixes
- With the engine cold, check the coolant level, and top up with the coolant specified for your car if it’s low.
- Check the sensor’s plug and wiring.
- Compare the coolant temperature in live data with the outside temperature on a cold engine, and watch it rise smoothly as the engine warms up.
- Replace the sensor if the wiring is fine, bleed the air out of the cooling system as the service information for your car describes, and clear the code.
Questions
Can I drive with P0115?
Gently, and only as far as you need to. The gauge and the temperature warning may not show overheating, and the cooling fan may not switch on, so the engine can overheat without warning. Check the coolant level when it’s cold. If you see steam, smell hot coolant or the heater suddenly blows cold, stop when it’s safe to do so and switch the engine off.
Why does my cooling fan run all the time?
On many cars, the engine computer runs the fan all the time when it can’t trust the coolant temperature, to be on the safe side. It should stop once the fault is fixed.
What is the difference between P0115 and P0128?
P0115 means the sensor’s signal is faulty. P0128 means the signal is fine but the engine takes too long to warm up, which usually points to the thermostat.