Engine Coolant Temperature Sensor Circuit 1 High Input
The PCM detected an abnormally high voltage signal from the engine coolant temperature (ECT) sensor circuit, indicating the sensor is reading colder than actual engine temperature or the circuit has an electrical fault. This causes the engine to run rich and cold, leading to poor fuel economy, rough idle, and black smoke from the exhaust.
What You Might Notice
- Check Engine Light (MIL) illuminated
- Very poor fuel economy
- Black smoke from exhaust
- Rough idle and misfiring
- Cold start difficulty or no-start condition
Most Common Causes
- 1
Bad ECT sensor
The coolant temperature sensor has failed internally or developed a short, causing it to send a high voltage signal to the PCM indicating cold temperatures.
- 2
Loose or corroded sensor connector
A poor electrical connection at the ECT sensor connector creates high resistance, causing the PCM to read an abnormally high voltage signal.
- 3
Open ground circuit
A break or corrosion in the ground wire between the ECT sensor and PCM prevents proper voltage return, causing the circuit to read high.
- 4
Shorted voltage supply wire
The positive voltage feed wire to the sensor is shorted internally or to another circuit, affecting the signal voltage the PCM receives.
How to Diagnose It
- 1
Check Bad ECT sensor — The coolant temperature sensor has failed internally or developed a short, causing it to send a high voltage signal to the PCM indicating cold temperatures.
- 2
Check Loose or corroded sensor connector — A poor electrical connection at the ECT sensor connector creates high resistance, causing the PCM to read an abnormally high voltage signal.
- 3
Check Open ground circuit — A break or corrosion in the ground wire between the ECT sensor and PCM prevents proper voltage return, causing the circuit to read high.
- 4
Check Shorted voltage supply wire — The positive voltage feed wire to the sensor is shorted internally or to another circuit, affecting the signal voltage the PCM receives.
How to Fix It
- 1
Inspect and clean ECT sensor connector
Remove the ECT sensor connector and inspect for corrosion, bent pins, or loose terminals. Clean with electrical contact cleaner and reassemble securely, then clear the code and test.
- 2
Replace engine coolant temperature sensor
Drain the coolant, remove the old ECT sensor from the engine block or intake manifold, and install a new sensor with the correct temperature range specification for your vehicle.
- 3
Check and repair wiring harness
Using a multimeter, test the ground and voltage supply wires connected to the ECT sensor circuit for continuity and shorts. Repair any damaged insulation or replace sections of the harness as needed.
- 4
Test PCM and verify sensor operation
After repairs, use a scan tool to monitor live ECT sensor data while the engine warms up. If readings remain incorrect, the PCM may need diagnosis or replacement.
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