Technical Definition:

Engine Coolant Temperature (ECT) (Sensor 1) Circuit Low

Technical Description:

The ECT (Engine coolant temperature) sensor is a thermistor located in the engine block or other coolant passage. It changes resistance with changes in temperature of the coolant that it’s in contact with. It’s usually a two wire sensor. One wire is a 5 volt reference from PCM (Powertrain Control Module) and the other is a ground supplied from PCM.

Possible Causes:

• Bad ECT sensor
• Short to ground on ECT signal circuit
• Faulty or damaged connectors
• Wiring harness damaged
• Loose terminals at ECT or PCM
• POSSIBLY an overheated engine
• Bad PCM

Possible Symptoms:

• MIL (Malfunction Indicator Lamp) illumination
• Poor fuel economy
• Poor drivability
• Engine may run rough or blow black smoke out the tailpipe
• May not idle
• May start and then die

Engine Coolant Temperature Circuit Low Input

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Low engine coolant level
– Faulty Engine Coolant Temperature (ECT) sensor
– Faulty engine coolant thermostat
– Engine Coolant Temperature (ECT) sensor harness is open or shorted
– Engine Coolant Temperature (ECT) sensor circuit poor electrical connection

Specific Makes: