What it means
The second 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 B controls coolant flow through a bypass path, and the control module compares its commanded operation with the resulting temperature behaviour. This code means valve B responds, but coolant temperatures do not change as expected, which can happen if the valve only moves partway or its temperature feedback is inaccurate.
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
- Engine temperature may fluctuate
- Heating or warm-up may be affected
How to diagnose it
- Review freeze-frame data and live coolant-temperature readings to identify whether the unexpected response occurs during warm-up or at operating temperature.
- Inspect valve B, its linkage, connectors, and nearby wiring for sediment, damage, or restricted movement.
- Command valve B through its available positions with a scan tool and compare the temperature response with the manufacturer's expected behaviour.
- Check for sediment that could make valve B stick partway or keep it from fully closing.
- Test valve B's return spring and temperature-sensor readings against the manufacturer's specification.
Common fixes
- Remove deposits that are restricting valve B's movement.
- Repair damaged wiring or connector contacts at valve B or its temperature sensor.
- Replace a weak return spring if it is separately serviceable.
- Replace a temperature sensor that is outside the manufacturer's calibration specification.
- Replace valve B if it cannot travel through its full range.
Can I keep driving?
If the temperature gauge remains normal, limit driving to short trips and monitor it closely. Avoid heavy loads, and stop if the engine overheats or cabin heat suddenly changes, since the valve's incorrect response can disrupt temperature control.
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.