What it means
The ECM detects a generic fault on the engine coolant temperature 4 sensor circuit. Reading cannot be used reliably for control.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Engine coolant temperature sensor 4 reports coolant temperature to the engine control module through its own circuit. The module sets this circuit fault when the sensor signal or its wiring cannot provide a reliable reading, which can disrupt temperature-based engine and fan control.
Common causes
Most likely first.
- Sensor failed
- Wiring or connector fault
Symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Cabin heater weak or excessively hot
- Possible long warm-up time or hard cold start
How to diagnose it
- Save freeze-frame data and compare sensor 4's reading with the other coolant-temperature readings and ambient temperature after the engine has cooled.
- Locate coolant temperature sensor 4 using the vehicle wiring diagram and inspect its connector and harness for damage, coolant intrusion, loose pins, or corrosion.
- Check the sensor 4 signal and reference or return circuits for continuity, shorts, and poor connections using the manufacturer's wiring information.
- Measure sensor 4's response as the engine warms and compare it with the manufacturer's specification and related temperature readings.
- If the wiring checks out but sensor 4 remains implausible or unresponsive, test or replace the sensor and verify fan and temperature readings afterward.
Common fixes
- Reconnect or clean the sensor 4 connector and secure the harness.
- Repair damaged or corroded wiring in the sensor 4 circuit.
- Replace coolant temperature sensor 4 if its signal fails the specified checks.
- Correct a poor sensor mounting or sealing condition if it prevents sensor 4 from sensing coolant properly.
Can I keep driving?
Check the temperature gauge and warning lights closely; stop if the engine overheats or coolant is lost, since an unreliable sensor reading can impair temperature control. Avoid extended driving until the cooling fan and sensor 4 readings are confirmed to work.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.