Faulty coolant temperature sensor (NTC thermistor) with a skewed resistance curve; Corroded, loose, or damaged wiring and connector pins at the sensor or DME; Air pockets or low coolant level causing the sensor to read air instead of coolant; Thermostat stuck open or closed, preventing the DME from seeing expected warm-up; Contamination or scale build-up on the sensor tip insulating it from coolant; DME software or adaptation values that need updating or resetting; Rare internal DME fault in the temperature input circuit

DTC codes / BMW codes / P1115

P1115 · BMWCoolant Temperature Sensor Plausibility

Q: What does code P1115 mean?

Coolant Temperature Sensor Plausibility. P1115 on BMW vehicles means the engine control module (DME) has detected an implausible coolant temperature signal during its rationality checks. The DME compares the coolant temperature sensor reading against other temperature inputs and expected warm-up behaviour, and flags the code when the signal does not make physical sense.

P1115 on BMW vehicles means the engine control module (DME) has detected an implausible coolant temperature signal during its rationality checks. The DME compares the coolant temperature sensor reading against other temperature inputs and expected warm-up behaviour, and flags the code when the signal does not make physical sense.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Erratic or inaccurate temperature gauge readings on the instrument cluster
Poor fuel economy or rough running during cold start and warm-up
Cooling fan running constantly or not engaging when it should
Incorrect cold-start enrichment causing a rich or lean condition
Occasional stalling or hesitation when the engine is warming up

Common causes, most likely first

Faulty coolant temperature sensor (NTC thermistor) with a skewed resistance curve
Corroded, loose, or damaged wiring and connector pins at the sensor or DME
Air pockets or low coolant level causing the sensor to read air instead of coolant
Thermostat stuck open or closed, preventing the DME from seeing expected warm-up
Contamination or scale build-up on the sensor tip insulating it from coolant
DME software or adaptation values that need updating or resetting
Rare internal DME fault in the temperature input circuit

How to diagnose and fix it

Check coolant level and bleed the cooling system to rule out air pockets
Inspect the sensor connector and wiring for corrosion, chafing, or loose pins
Measure the coolant temperature sensor resistance cold and hot, comparing to BMW specifications
Use a scan tool to compare the coolant temperature reading with intake air and oil temperature during a cold start
Test the thermostat operation by monitoring warm-up time and upper hose temperature
Replace the coolant temperature sensor if resistance testing is out of specification
Clear adaptations and the fault memory, then road test to confirm the code does not return

Plausibility checks catch what resistance tests miss

A sensor can pass a simple resistance test at two temperatures yet still fail the DME plausibility check because its response curve is non-linear or slow to react.
Air trapped in the cooling system after a repair is one of the most common causes of P1115 on BMW engines, and it often sets without any sensor fault at all.
A thermostat that is stuck open can trigger P1115 because the DME never sees the expected warm-up rate, even though the coolant sensor itself is healthy.
Comparing the coolant temperature PID with intake air and oil temperature on a cold start is the fastest way to spot a skewed sensor before replacing parts.
On some BMW models, a low or weak battery can cause implausible temperature readings at cold start, so check battery condition before condemning the sensor.

Can I keep driving with P1115?

You can usually drive the car to a workshop, but avoid hard acceleration and long trips until the fault is diagnosed. If the temperature gauge behaves erratically or the engine overheats, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.