A coolant temperature sensor is a pretty simple electrical device which has a resistor built in that is sensitive to temperature. It has a plug on one end and a probe on the other end that extends into the coolant. It is either screwed or pressed into position and usually fairly easy to replace. Usually it is located on an engine’s cylinder head near the thermostat housing.
Sensor diagnosis is generally done by taking a measurement of the coolant temperature, reading the resistance of the sensor with a multimeter, and comparing the results to a chart to verify accuracy. In many cases it would begin with a trouble code, as the PCM monitors the coolant temperature sensor. There are many possible codes, but common generic sensor codes would be P0115, P0116, and P0117.
Cost of Coolant Temperature Sensor Replacement
To illustrate, here are estimates of the coolant temperature sensor price on some common vehicles using a labor rate of $150 per hour:
- 2010 Ford Fusion 3.0-liter engine – it usually takes half an hour of labor to replace the sensors. A GDP replacement sensor costs about $36 which would make the replacement cost about $110.
- 2013 Journey 3.6-liter engine – the labor time for sensor replacement is 0.6 of an hour. An OE Mopar sensor costs about $54 and a Standard replacement sensor costs about $28. This would make the job about $144 using factory parts, and about $118 using aftermarket parts.
- 2006 Volkswagen Jetta 2.5-liter engine – the estimated labor time for sensor replacement for this vehicle is 0.6 of an hour. A factory replacement costs around $60 while an NTK replacement sensor is about $40. That would make the job about $150 using OE parts, or about $130 using aftermarket parts.
- 2010 Toyota Camry with a 2.5-liter engine – the labor time for sensor replacement is 1.6 hours. An OE Denso sensor costs about $76 and an ACDelco replacement sensor is about $50. That would make the job about $316 using OE parts, or about $290 using aftermarket parts.
Other Cost Considerations
When the sensor is removed, the coolant is lost. Sometimes, the coolant can be drained into a clean container and re-used, but this isn’t always practical and the draining process itself can introduce contaminants. It’s normal for a charge to be added for replacing coolant as necessary. Depending on how the sensor is placed, the quantity might be a small amount or it might be as much as a gallon. Coolant costs vary from about $7 a gallon to as much as $50 a gallon for some factory brands.
Before a sensor is replaced, it ordinarily must be diagnosed and most shops have a flat one-hour diagnostic charge for that. Sometimes, a sensor can trigger a trouble code and turn on the engine light. In the event of a failed or inaccurate coolant temperature sensor, a generic OBDII code such as P0116 could be triggered. This would have a diagnostic procedure to verify the failure and it is generally most economical to go through the diagnostic procedure to rule out other possible causes and verify the failure before replacing parts.
What is the Coolant Temperature Sensor For?
The coolant temperature sensor is usually located near the top of the engine; either in a cylinder head coolant passage or at the thermostat housing. Its role is to inform the engine management system of the engine temperature which uses that information to adjust fuel mixtures and timing, as well as to know when to turn on the cooling fans.
The temperature information from the sensor is also displayed on a dash gauge, or sometimes just used to trigger a warning light in the event of an overheating condition.
There are a couple of other coolant sensors that this shouldn’t be confused with. Many vehicles have a coolant level sensor (usually on the coolant reservoir) which can trigger a dash light or warning if the coolant level gets below a certain point. Some older vehicles also use a coolant switch – most often in the radiator housing – to directly control the cooling fans.
What Happens When the Coolant Temperature Sensor Fails?
Most engines have a thermostat that is designed to maintain the engine temperature at about 200 degrees once the vehicle is warmed up. If there is a gauge on the dash, typically, that would be right at the halfway mark.
If the thermostat is operating normally but the coolant temperature sensor isn’t, that should show up as a problem on the dash gauge reading.
Once the engine has reached operating temperature, the cooling fans will cycle on and off to maintain that temperature. They rely on information from the coolant temperature sensor to do that. If the fans don’t come on as they should or if they stay on excessively, that can indicate a faulty sensor.
One of the more important jobs of the coolant temperature sensor is to inform the engine management system of the engine temperature. When the engine is cold, the fuel mixture must be richer to allow smooth firing and power output. When the engine is hot, the mixture must be made leaner to prevent detonation and plug fouling. These require accurate coolant temperature data. Rough running when cold is one possible symptom. Poor performance and loss of power when warm is another, as is generally poor fuel mileage.
Frequently Asked Questions
They don’t have any moving or wearing parts, so they can last indefinitely. There is no maintenance or expected replacement time.
Yes, as long as it is accessible. If you can find it on the engine, you can probably replace it. Be careful of hot coolant, of course. And take care to refill and purge the air from the cooling system afterward.
In most cases it takes about a half hour. Some engines (such as the Chrysler 3.6) take longer, due to the work needed to do to access the sensor.
As long as the failure doesn’t result in overheating, then it should be safe. Though the fuel mixtures might be affected, which would reduce mileage and long-term could harm the engine.