P0117 indicates that the voltage signal from the engine coolant temperature (ECT) sensor 1 is lower than the expected range, suggesting a short to ground or an open circuit in the sensor circuit. The powertrain control module (PCM) sets this code when it detects a voltage below the calibrated minimum for the sensor.
The sensor element may develop an internal short, pulling the signal voltage low regardless of coolant temperature.
Damaged insulation or a pinched wire can create a direct path to ground, lowering the sensor voltage.
Corrosion or a poor connection at the sensor plug can cause a low‑voltage reading.
A broken ground wire or high resistance in the ground path can prevent the sensor from reaching its normal voltage range.
An internal driver or ADC failure in the PCM can misinterpret the sensor signal, but this is uncommon compared to sensor or wiring issues.
No. The code indicates a low voltage signal from the coolant temperature sensor circuit, not an actual high coolant temperature.
The vehicle may run, but fuel management and emissions control can be impaired; repair is recommended to avoid further drivability issues.
PCM replacement is rarely needed; the majority of cases are resolved by repairing the sensor, wiring, or connector.
Use a multimeter to measure the sensor’s resistance at several known temperatures (e.g., ice water, room temperature, boiling water) and compare the readings to the service manual specifications.