Common Symptoms
- Check Engine Light illuminated
- Poor fuel economy
- Hard starting when engine is cold
- Engine runs rough or hesitates during warm-up
- Cooling fans run continuously or not at all
- Inaccurate temperature gauge readings
Most Likely Root Causes
- Faulty engine coolant temperature sensor
- Damaged or corroded wiring harness to ECT sensor
- Poor electrical connection at ECT sensor connector
- Shorted or open circuit in ECT sensor wiring
- Failed engine control module
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Component Location
The engine coolant temperature sensor is typically threaded into the engine block, cylinder head, or intake manifold near the thermostat housing.
Manufacturer Notes
Some manufacturers use different ECT sensor locations or dual sensors for redundancy which may affect diagnostic approach.
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Heavy-duty trucks often throw both OBD-II and J1939 faults simultaneously. AI Diesel Tech handles both protocols in a single guided session.
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