Is there more than one coolant temperature sensor on my car?

Many cars have two: one that feeds the ECU and controls fuelling, and a separate sensor for the dashboard gauge or electric fan thermostat. They are not always interchangeable — match by part number.

Can a faulty coolant temperature sensor cause overheating?

If the sensor reads high permanently, the ECU may lean out the mixture and reduce idle speed as if the engine is fully warm, leading to running problems. If it controls the cooling fan and fails, the fan may not run, causing overheating in traffic.

How do I test a coolant temperature sensor?

Measure resistance across the sensor terminals at known temperatures — a known-good NTC sensor will show high resistance when cold (several thousand ohms) and low resistance when hot (around 50 to 300 ohms). Compare to the manufacturer's specification chart.

Should I change the coolant when I replace the sensor?

If the coolant is discoloured, acidic, or due for renewal, yes — old coolant degrades sensor accuracy over time by attacking the sensing element with corrosion.

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Coolant Temperature Sensor buying guide — what to know before you buy

The coolant temperature sensor — also called the water temperature sensor, engine temperature sensor, or CTS — measures the temperature of the engine coolant and feeds this data to the ECU to control fuelling, ignition timing, idle speed, and the cooling fan. A failed or drifting sensor causes cold-start richness, overheating without a warning light, or a permanently illuminated temperature gauge. Sensor, coolant temperature failures are common on high-mileage engines where the sensing element corrodes from prolonged contact with acidic coolant. CarParts247 stocks OEM and aftermarket coolant temperature sensors from Bosch, Continental, Hella, and NTK for virtually every petrol and diesel engine.

Symptoms of a faulty coolant temperature sensor

The ECU relies heavily on coolant temperature to determine fuel enrichment during warm-up. A faulty CTS disrupts this and has knock-on effects across multiple engine systems.

Engine runs rich and drinks fuel — sensor reads artificially cold
Temperature gauge reads incorrectly or is erratic
Engine overheats without triggering the warning light — sensor reads artificially hot
Electric cooling fan runs continuously or not at all
DTC codes P0115 to P0119 (coolant temperature sensor range and circuit fault)

Replacing the sensor

The CTS is typically threaded into the thermostat housing, coolant outlet, or a tapping in the cylinder head. Drain enough coolant to drop the level below the sensor before removing it to avoid a large spill. Use a crow-foot spanner or deep sensor socket and tighten the new sensor to the specified torque — overtightening cracks the plastic housing.

Apply a small amount of PTFE tape or thread sealant to the thread if the sensor uses a tapered pipe thread. If it uses a straight thread with a sealing washer, do not use additional sealant.

Fit a new sealing washer or O-ring if supplied
Top up coolant and bleed the system before starting
Clear fault codes and perform a full warm-up cycle to verify the gauge and fan operation
Check that the new sensor has the correct number of terminals — single and dual-pin types exist