What it means
Voltage on the engine coolant temperature 4 sensor signal line is above the expected window. Wire shorted to B+ or sensor open.
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-high code means the signal voltage is above the expected range, often because the signal wire is shorted to power or the sensor circuit is open.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- 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 compare sensor 4 live data with the actual cold-engine condition and other coolant-temperature readings.
- Locate sensor 4 from the wiring diagram and inspect its connector and harness for an unplugged connection, broken wire, corrosion, or contact with a power feed.
- Check the sensor 4 signal wire for a short to power and verify connector pin contact using the manufacturer's wiring information.
- Test for an open sensor element or open circuit in the sensor 4 wiring, following the manufacturer's specified isolation procedure.
- If the sensor and harness are sound, check the module input circuit using the manufacturer's diagnostic procedure.
Common fixes
- Reconnect and secure a loose sensor 4 connector.
- Repair an open or damaged wire in the sensor 4 circuit.
- Repair a sensor 4 signal wire that is shorted to a power feed.
- Replace coolant temperature sensor 4 if its element is open.
Can I keep driving?
Monitor the temperature gauge and warning lights, and stop if the engine overheats or coolant is lost. Because an implausible sensor 4 signal may affect cooling fan operation, avoid long drives until the fault is fixed.
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.