P0117 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Safe to drive for a short time, but the engine may run rich and burn extra fuel, and the cooling fan may run constantly.

What P0117 means on a Mercedes-Benz

On a Mercedes-Benz, P0117 means the engine coolant temperature sensor is reporting full hot because its voltage is too low. A failed sensor or a wiring short is the usual cause. The computer may run the engine rich and keep the cooling fan on.

Is P0117 common on Mercedes-Benzs?

C-Class, E-Class, and GLK models can see P0117 with age, usually from a failing sensor or connector corrosion. Mercedes coolant sensors are reasonably priced, and the repair is quick once the fault is confirmed.

Commonly reported on: C-Class, E-Class, GLK-Class, ML-Class.

Symptoms

Check engine light on
Cooling fan runs constantly
Poor fuel economy from rich running
Hard starting when the engine is cold

Common causes

most common: Faulty coolant temperature sensor
common: Sensor wiring shorted to ground
common: Corroded or loose connector terminals
less common: Damaged wiring near the sensor

How to fix it

Fix	DIY?	Typical cost
Replace the coolant temperature sensor	Yes	$30–80
Repair the wiring or connector	Mechanic	$80–200
Have a shop replace the sensor and verify the circuit	Mechanic	$160–300