Skip the auto shop - Our mechanics make house calls

Symptoms of a Bad or Failing Coolant Temperature Switch (Sensor)

Coolant Temperature switch

Bad or Failing Coolant Temperature Switch (Sensor) Inspection

by a top-rated mechanic at your home or office

The coolant temperature sensor, also known as the coolant temperature switch, is an engine management system sensor that is used to monitor the temperature of the engine’s coolant. Most coolant temperature sensors operate using electrical resistance to measure the temperature of the coolant. This signal is then sent to the computer so that changes can be made to the engine’s timing and fuel calculations for optimal performance, as engines require more fuel when they are cold, and less fuel when they are fully warmed up. The computer will also scale back engine performance settings if it detects that the engine temperature is too high, in order to protect the engine from possible damage due to overheating.

Because temperature plays such a vital role in engine performance calculations, any problem with the coolant temperature sensor can quickly translate into an engine performance issues. Usually a problem with the coolant temperature sensor will cause a few symptoms that alert the driver of a potential problem that should be thoroughly inspected.

HAVE SYMPTOMS OF CAR TROUBLE?
Get an $80 diagnostic
by a top-rated mechanic at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

1. Poor fuel economy

One of the first symptoms associated with a problem with the coolant temperature sensor is poor fuel economy. If the coolant temperature sensor goes bad it can send a false signal to the computer and throw off the fuel and timing calculations. It is not uncommon for the coolant temperature sensor to fail and send a permanently cold signal to the computer. This will cause the computer to think the engine is cold, even when it is not, and as a result will use more fuel than necessary. This will reduce fuel economy, and may hinder engine performance.

2. Black smoke from engine

Another symptom of a possible problem with the coolant temperature sensor is black smoke from the vehicle’s exhaust. If the coolant temperature sensor fails and sends a cold signal to the computer, this can confuse the computer and cause it to unnecessarily enrich the fuel mixture. If the fuel mixture becomes excessively rich to the point where the fuel cannot be adequately burned in the combustion chamber, it will burn up in the exhaust pipes and cause black smoke. In severe cases, the black smoke may be considerable enough to warrant not driving the vehicle.

HAVE SYMPTOMS OF CAR TROUBLE?
Get your car fixed at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

3. Overheating engine

Another symptom of a problem with the coolant temperature sensor is an overheating engine. The coolant temperature sensor can also fail in a manner that causes it to send a permanently hot signal. This can cause the computer to incorrectly compensate for a lean signal, which can result in overheating, and even misfires or engine ping.

4. Check Engine Light comes on

An illuminated Check Engine Light is another symptom of a potential problem with the coolant temperature sensor. For some vehicles the computer will set off a Check Engine Light if it detects a problem with the sensor’s signal or circuit. The Check Engine Light will remain on until the issue is addressed.

The coolant temperature sensor is one of the most important engine management sensors, as its reading plays a key role in calculations which affect engine performance. For this reason, if you suspect that your coolant temperature sensor is having an issue, have the vehicle inspected by a professional technician from YourMechanic. They will be able to diagnose your vehicle and determine if you need a coolant temperature switch replacement.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP)...


Related questions

Q: Blue smoke after starting the car

Blue smoke usually indicates oil getting into the combustion process - not a good thing. If you had your oil changed the day before, check the oil level to make sure it wasn't over-filled. If you car is accumulating some...

Q: Car runs hot when idling

Hello! If a vehicle only overheats when sitting, it usually indicates that there is an issue with the radiator fans. It cools back down due to the rushing air that is created by moving, which momentarily acts as a fan...

Q: Why Won't My Car Start?

There are many reasons why your car may not start. Some common causes include a dead battery, faulty starter or starter relay, fuel pump issues, clogged fuel filter, and computer or sensor issues depending on the year of your vehicle....