Code Definition

P0118 — Engine Coolant Temperature Circuit High Input

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0118

P0118 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0118 is stored, the module has detected a signal or supply voltage higher than the expected operating range.

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.

Because P0118 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The engine coolant temperature sensor is a negative temperature coefficient thermistor whose resistance falls as coolant temperature rises, with the ECM measuring the resulting voltage across a pull up resistor. P0118 sets when signal voltage exceeds the upper threshold for a calibrated period, corresponding to very high circuit resistance and therefore an implausibly cold indicated coolant temperature, typically pinned at the bottom of the scale near minus 40 degrees Celsius. The usual causes are an open circuit in the signal or ground wiring, a high resistance connection, a sensor with an in...

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