Engine Coolant Temperature Sensor Circuit Low Input
The P0117 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the engine coolant temperature (ECT) sensor that is lower than the expected range (typically below 0.2 volts). This usually means the sensor is reading an extremely cold temperature or there is a short to ground in the sensor circuit. The ECT sensor is a thermistor that changes resistance with temperature; low voltage suggests low resistance, often due to a short circuit or a failed sensor.
1. Most Common Causes
- Faulty engine coolant temperature sensor
- Short to ground in the ECT sensor signal circuit
- Open or shorted wiring in the ECT sensor harness
- Poor electrical connection at the ECT sensor connector
- Corroded or damaged sensor terminals
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Hard starting, especially when cold
- Poor fuel economy
- Engine running rich or black smoke from exhaust
- Engine overheating or running too cool
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the ECT sensor connector and wiring for damage, corrosion, or loose connections.
Step 3: Disconnect the ECT sensor and measure its resistance with a multimeter; compare to manufacturer specifications (e.g., 2-3 kΩ at 68°F).
Step 4: Check for voltage at the sensor connector with the ignition on; should be around 5V reference. If low, check for shorts to ground in the wiring.
Step 5: If sensor and wiring are good, test the ECM by backprobing the signal wire and monitoring voltage while varying sensor temperature.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with P0117 for extended periods. The engine may run poorly, overheat, or cause damage to the catalytic converter due to a rich fuel mixture.
How much does it cost to fix?▼
The typical repair cost ranges from $50 to $150, including parts and labor. The sensor itself is usually $20-$50, and labor is about $30-$100 depending on accessibility.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.