What it means
The fourth coolant bypass valve responds to commands but the resulting coolant temperature behaviour is not as expected.
At a glance
- Usually lights the check-engine light
How it works
Coolant bypass valve D routes coolant through a particular part of the cooling system, and the control module commands it as engine conditions change. This code sets when valve D responds but its operation or the resulting coolant-temperature behavior falls outside the expected range, such as when it moves sluggishly or fails to close fully.
Common causes
Most likely first.
- Valve partially stuck by sediment
- Weak return spring fails to close fully
- Sensor element aged beyond calibration window
Symptoms
- Check-engine light may be on
- Engine warms up slowly or coolant temperature fluctuates
- Cabin heat may be reduced or inconsistent
How to diagnose it
- Review freeze-frame data and live coolant temperature during warm-up to see whether the fault coincides with slow warming, temperature swings, or inconsistent cabin heat.
- With the engine cool, inspect valve D, its connector, and nearby coolant passages for sediment, leaks, or damage that could restrict movement.
- Use a scan tool, if supported, to command valve D through its available positions and compare its response with the manufacturer's expected behavior.
- Check relevant coolant-temperature sensor readings for plausibility and compare them with the manufacturer's specification before attributing the fault to valve D.
- If wiring and sensor readings are sound, test valve D for sticking or weak return action according to the manufacturer's procedure.
Common fixes
- Repair loose or damaged valve D wiring or connector contacts found during inspection.
- Clean sediment from valve D or its passage if permitted by the manufacturer's service procedure.
- Replace valve D if it sticks or its return action is weak.
- Replace a temperature sensor only if testing confirms it is outside its calibration specification.
Can I keep driving?
If temperature remains stable, brief local driving may be possible, but monitor the gauge and avoid heavy loads until the valve fault is resolved. Stop if the engine overheats; poor coolant routing can also reduce or disrupt cabin heat.
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.