Today’s vehicles rely on complex network of sensors which monitor engine efficiency. But when just one sensor fails, an array of concerning symptoms can emerge.
The engine coolant temperature sensor is especially vulnerable. Its failure can lead to severe issues. Let’s look at the common symptoms of a faulty coolant temp sensor, why it fails, and its typical replacement cost.
Bad Coolant Temperature Sensor Symptoms
With time, coolant temperature sensors in many vehicles have a tendency to fail. In most cases, this comes as a result of continuity loss within the sensor itself.
When this occurs, a false temperature value is sent to the vehicle’s ECM, which leads to improper system response. As a result several symptoms often present themselves in short order.
The following are 7 of the most common symptoms associated with a failing engine coolant temp sensor.
#1 – Check Engine Light
One of the most common symptoms associated with engine coolant temperature sensor failure is the sudden appearance of a check engine light. By its nature, a vehicle’s on-board diagnostics system stores trouble codes associated with many component failures and electrical circuit related problems.
If a vehicle’s ECM detects the delivery of irrational data from one of its sensors, a check engine light is illuminated. This light will remain on until the offending code is cleared, or the corresponding malfunction is remedied.
#2 – Poor Fuel Economy
Another symptom commonly associated with the failure of a coolant temperature sensor is poor fuel economy.
This stems from the fact that coolant temperature sensor feedback plays a vital role in the calculation of fuel delivery and timing. More often than not, a faulty engine coolant temperature sensor will incorrectly reflect a cool temperature reading.
When a permanently cool signal is sent by a coolant temperature sensor, a vehicle’s ECM attempts to compensate for this condition by dosing more fuel than is needed. In the end, this is reflected by more frequent trips to the pump.
#3 – Dark Colored Exhaust
As previously mentioned, a faulty coolant temperature sensor that has defaulted to a permanently cold reading will typically cause an engine to over-fuel (aka: run rich). As a result, excess unburnt fuel is passed downstream, where it often ends up entering the exhaust system.
When this excess fuel burns within a vehicle’s exhaust system, dark grey or black colored smoke is produced as a byproduct. In severe cases, this smoke can become very dense, and quite noticeable to anyone nearby.
#4 – Engine Overheating
One of the most severe symptoms of coolant temperature sensor failure is engine overheating. While some vehicles utilize an auxiliary temperature sensor to regulate fan operation, the vast majority of makes and models rely upon the engine coolant temperature sensor to sustain this function.
If an engine coolant temperature sensor of this type fails, it is common for the vehicle’s radiator fan to be inoperable. As a result, engine temperatures begin to spike, risking damage to other components.
#5 – Fluctuating Temperature Gauge
If the coolant temp sensor isn’t working correctly, it can provide inaccurate readings, affecting your temperature gauge and making it fluctuate. This might lead you to think your engine is overheating when it’s not, or vice versa.
Stay aware, as these wrong readings can cause unnecessary panic or even lead to potential engine damage if an actual overheating issue goes unnoticed.
#6 – Rough Idling
Due to incorrect temperature readings, your vehicle’s computer may adjust the air-fuel mixture improperly, causing an uneven and rough idle. It’s essential to keep an eye on this, as it could make your driving experience less comfortable and may lead to more significant issues.
#7 – Hard Start at Certain Temperatures
Though not as common as other symptoms, a hard start condition is occasionally presented by a faulty coolant temperature sensor. In most cases, this condition will present itself only when a vehicle’s engine is at one particular temperature, whether hot or cold.
On most occasions, this is the result of a sensor which is providing a continually hot reading, even when an engine is actually cool. As a result, this typically renders a lean condition, which exponentially increases crank times.
Engine Coolant Temperature Sensor Replacement Cost
The cost associated with coolant temperature sensor replacement can vary significantly from one model of vehicle to the next.
While the coolant temperature sensors found on many vehicles are relatively simple to replace, others can be quite difficult to access. The actual cost associated with the purchase of a coolant temperature sensor can also vary by vehicle.
On average, the cost of a coolant temperature sensor ranges from $20-$80, while the cost of labor ranges from $50-$250. In total, one could expect to pay $70-$330 to have their engine coolant temperature sensor replaced.
How an Engine Coolant Temperature Sensor Works
Internal combustion engines rely upon the use of a type of coolant to regulate operational engine temperatures. Coolant cycles through an engine’s cylinder heads and block, where it picks up heat that is produced as a byproduct of the combustion process.
Coolant is then directed to the radiator, where incoming airflow dissipates heat stored within the coolant. As its name would suggest, a vehicle’s coolant temperature sensor monitors the temperature of the coolant flowing throughout an engine.
This information is then relayed to the vehicle’s ECM (Engine Control Module), where it is used as an input when determining how best to regulate various engine functions. These functions include fuel metering, EGR operation, and fan engagement. This data is also displayed to the driver via a temperature gauge in the dashboard.
For a more technical explanation of how the sensor works, check out this video:
Where is the Engine Coolant Temperature Sensor Located?
In most vehicles, the coolant temperature sensor can be found near the engine thermostat. On many late-model vehicles, this sensor is often threaded into the thermostat housing itself.
Now, the thermostat housing is usually located on the cylinder head, close to the intake manifold. This part of the engine is designed to help regulate the circulation of coolant within your vehicle’s cooling system. So, it makes sense that the coolant temperature sensor would be placed close by. It’s the best spot for capturing accurate temperature readings from your coolant.
Keep in mind that some vehicles might have more than one coolant temperature sensor. In these cases, you’ll typically find one sensor near the thermostat housing, like already mentioned, and another one elsewhere, such as near the radiator or in the lower engine block.
This is to ensure that the engine control module (ECM) receives precise, real-time data on the whole system’s temperature fluctuations.
Causes of Sensor Failure
#1 – Low Coolant Level
One of the common reasons for a faulty coolant temperature sensor is a low coolant level. Suppose your coolant level is too low; it can cause air pockets to form in the cooling system, which leads to incorrect readings from the sensor.
In turn, this can affect the engine management system, resulting in issues like wrong fuel injection, poor fuel economy, and an overheating engine.
#2 – Air Pockets
As mentioned above, air pockets can lead to fluctuations in coolant temperature, which could cause erratic readings from the sensor. A cooling system flush might help eliminate the air pockets and improve sensor performance.
If you notice your cooling fans cycling erratically, one potential reason could be air in the system causing the sensor to send faulty signals.
#3 – Corrosion and Bad Connections
Over time, corrosion can build up on the engine coolant temperature sensor connections, causing a poor connection between the sensor and the engine management system. This weak connection can lead to incorrect readings and may trigger a trouble code.
#4 – Damaged Wiring and Connectors
Damage to wiring and connectors can also lead to a malfunctioning coolant temperature sensor. The coolant temperature sensor is connected to the engine management system using wiring and plastic hoses. If the wiring or connectors are damaged, this can cause incorrect readings from the sensor, and potentially even total failure of the sensor.
In these situations, it’s necessary to inspect all related wiring and connectors for damage and replace any damaged components.
Can You Drive With a Faulty Coolant Temp Sensor?
While a vehicle with a faulty coolant temperature sensor can often be driven from one location to the next, doing so is not advised. With time, many of the individual symptoms of a failing coolant temperature sensor can become problematic themselves.
An inoperable fan caused by a faulty coolant temperature sensor will quickly result in engine overheating. As a result, additional problems, such as head gasket leaks, can arise.
Likewise, abnormally high fuel rates caused by skewed data from a faulty sensor, can lead to the superheating and failure of a vehicle’s catalytic converter.
How to Diagnose a Bad Coolant Temperature Sensor
So, you’ve been noticing some weird stuff going on with your car’s engine temperature? Maybe it’s time to check out that coolant temp sensor. Don’t worry, diagnosing a bad coolant temperature sensor is something you can do. Let’s walk through it step by step.
#1 – Check Coolant Level
First things first, make sure your coolant level is good. You don’t want to misdiagnose a simple low coolant issue as a faulty sensor. Just pop the hood, locate the coolant reservoir, and check the level. If it’s low, top it off and see if your engine temperature issues persist.
#2 – Inspect Cooling Fans
Now, if your coolant level is fine, it’s time to check out the electrical cooling fans. These bad boys help keep your engine cool, and if they’re not coming on at the proper time, your engine temperature can skyrocket.
Start your engine and watch the cooling fans. They should kick on when the engine reaches a certain temperature or when the AC is turned on. If they don’t come on as expected, it might be the coolant temperature switch causing the problem.
#3 – Scan for Trouble Codes
Grab your trusty scan tool and connect it to your car’s OBD-II port. This little gadget will let you know if there are any stored trouble codes related to the coolant temperature sensor. If you see one or more codes, take note of them and do some research on what they mean. These codes can help you pinpoint the issue.
At this point, if you suspect the coolant temperature sensor is the issue, you should consider having a mechanic take a closer look if you don’t feel confident in replacing the sensor yourself. The pros will have the proper tools and expertise to accurately diagnose and replace the faulty sensor if needed.
Can a Bad Coolant Temp Sensor Affect the Thermostat?
Yes, a malfunctioning coolant temperature sensor can affect the thermostat in your vehicle. The coolant sensor is responsible for sending temperature information to the engine control unit (ECU).
If it’s not functioning correctly, it can send incorrect temperature readings, causing the thermostat to open or close at the wrong time. This can lead to your engine overheating or running inefficiently, affecting the overall performance and fuel economy of your vehicle.
How Many Coolant Temperature Sensors Does a Car Have?
In most vehicles, there is usually only one coolant temperature sensor responsible for monitoring the engine’s temperature. However, some vehicles may have multiple sensors in different locations to monitor the temperature of specific parts in the cooling system, such as the radiator or the heater core.
Having multiple sensors helps the ECU to regulate the various functions related to the cooling system more effectively, such as controlling the cooling fans, thermostat operation, and even the heating and air conditioning systems.
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