P0117 on BMW: Causes, Symptoms and Fix Cost

P0117 means the engine coolant temperature (ECT) sensor circuit voltage is too low, which the ECU reads as an implausibly high temperature. Because the sensor is a thermistor whose resistance falls as it heats, a short to ground or a shorted sensor produces a low voltage that mimics extreme heat. The ECU often responds by running the cooling fan at full speed. Repair typically costs 40 to 180 EUR for a sensor or wiring fix.

Beyond the generic causes listed on the main P0117 page, these are the BMW-specific patterns we see most often:

Follow these steps to pinpoint the root cause of P0117:

1. Read the code and watch the live coolant temperature PID with Skanyx. P0117 typically shows the maximum value (often around 120 C or higher) even on a cold engine, which is a clear sign of a low-voltage short rather than a real overheat
2. Compare the live coolant reading against actual engine temperature by touching the upper radiator hose; if the engine is cold but the PID reads hot, the circuit is shorted
3. Unplug the sensor connector and check whether the reading drops to the open-circuit default; if it does, the sensor itself is likely shorted internally
4. Inspect the connector and harness for corrosion, moisture, or a chafe point shorting the signal wire to ground or to the sensor body
5. Measure the sensor resistance with a multimeter and compare to the manufacturer table; an abnormally low resistance confirms a failed sensor
6. If the sensor and connector are good, test the signal wire for a short to ground back toward the ECU

Estimated repair costs on a BMW (BMW parts and labour typically run 30% above the average for this code).

These codes commonly cluster with P0117 on BMW vehicles: