Code Definition

P1255 — Engine coolant temperature sensor short to ground

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Audi

About P1255

P1255 is a manufacturer-specific powertrain diagnostic trouble code recorded for Audi vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1255 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1255 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The engine coolant temperature sensor is a negative temperature coefficient thermistor screwed into the coolant flange, and its resistance falls as coolant temperature rises. The Engine Control Module supplies the sensor with a 5V reference through an internal pull up resistor and reads the resulting voltage on the signal wire, so a cold engine produces a high signal voltage and a hot engine a low one. DTC P1255 is stored when the module sees the coolant temperature signal pulled to or very near zero volts, a value lower than the sensor could ever produce even at extreme temperature, which it ...

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