What it means
Voltage on the engine coolant temperature 4 sensor signal line is below the expected window. Wire shorted to ground or sensor short.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Coolant temperature sensor 4 sends a temperature-dependent signal to the engine control module. This circuit-low code means the signal voltage is below the expected range, commonly because the signal is shorted to ground or the sensor itself is shorted.
Common causes
Most likely first.
- Signal wire shorted to ground
- Internal sensor short
- Connector pins corroded - high contact resistance
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 check whether sensor 4 live data is implausibly hot or otherwise inconsistent with a cold engine and the other temperature readings.
- Identify sensor 4 from the wiring diagram and inspect its connector and harness for crushed insulation, grounding, corrosion, or coolant contamination.
- Check the sensor 4 signal wire for a short to ground and inspect connector pins for unintended contact, using the manufacturer's circuit information.
- With the circuit isolated as specified by the manufacturer, test sensor 4 for an internal short and check the signal circuit for continuity.
- If the sensor and wiring pass their checks, verify the module input circuit using the manufacturer's diagnostic procedure.
Common fixes
- Clean and correctly seat the sensor 4 connector.
- Repair a sensor 4 signal wire that is shorted to ground or has damaged insulation.
- Repair corroded or loose connector pins in the sensor 4 circuit.
- Replace coolant temperature sensor 4 if it is internally shorted.
Can I keep driving?
Watch for overheating and stop driving if the temperature warning appears, coolant is lost, or the engine behaves abnormally. A false sensor 4 reading can interfere with fan control, so avoid extended trips until the circuit is repaired.
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.