Engine Coolant Temperature Sensor Circuit High Input
The P0118 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the Engine Coolant Temperature (ECT) sensor that is higher than the expected range, typically above 4.9 volts. This usually means the sensor circuit has an open or high resistance, often due to a faulty sensor, damaged wiring, or a poor connection. The ECT sensor is a thermistor that changes resistance with temperature; a high voltage reading corresponds to a very cold engine reading, which can cause the ECM to enrich the fuel mixture and potentially trigger other issues.
01. Most Common Causes
- Faulty Engine Coolant Temperature (ECT) sensor
- Open or shorted wiring in the ECT sensor circuit
- Poor electrical connection at the ECT sensor connector
- Corroded or damaged terminals
- Faulty Engine Control Module (ECM) (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Hard starting, especially when cold
- Poor fuel economy
- Engine running rich (black smoke from exhaust)
- Engine overheating or running too cool
- Rough idle or stalling
03. Step-by-Step Diagnosis
Step 1: Connect an OBD2 scanner and confirm the P0118 code. Check for any additional codes.
Step 2: Visually inspect the ECT sensor connector and wiring for damage, corrosion, or loose connections.
Step 3: Using a multimeter, measure the resistance of the ECT sensor at the connector. Compare to manufacturer specifications (typically 2000-3000 ohms cold, 200-300 ohms hot).
Step 4: Check the voltage signal at the ECM connector with the sensor disconnected; should be around 5V reference. If not, check for open or short in wiring.
Step 5: If sensor and wiring are good, suspect a faulty ECM (rare). Perform a continuity test between sensor and ECM.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with P0118. The incorrect coolant temperature reading can cause the engine to run rich, leading to poor fuel economy, catalytic converter damage, and potential overheating. You may be able to drive to a repair shop, but monitor the temperature gauge closely.
How much does it cost to fix?▼
The cost to fix P0118 typically ranges from $50 to $150. This includes the part cost for a new ECT sensor (usually $20-$50) and labor (0.5-1 hour). If wiring repairs are needed, costs may be higher.