Code Definition

P1118 — Engine Coolant Temperature Above Maximum Voltage/-40 F

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

About P1118

P1118 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

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.

P1118 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

This DTC is set when the Engine Control Module (ECM) detects that the Engine Coolant Temperature (ECT) sensor voltage is above a calibrated maximum threshold, corresponding to an extremely low and implausible coolant temperature, typically around minus 40 degrees F. The ECT sensor is a negative temperature coefficient (NTC) thermistor, and a high voltage condition indicates an open circuit or sensor failure causing the ECM to interpret the engine as excessively cold. With the engine reading falsely cold, the ECM commands an over rich mixture, which can cause hard hot starting, rough running, f...

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