What it means
The ECM has not learned the end-stop calibration for exhaust flow control valve B. Position cannot be commanded with full precision until adaptation completes.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Exhaust flow control valve B adjusts exhaust routing, for example to manage back-pressure or sound. The engine control module has not learned valve B’s end positions, so it may not be able to command the valve accurately until the required adaptation is completed.
Common causes
Most likely first.
- Adaptation lost after battery disconnect or ECM reset
- Valve replaced without learn procedure
Symptoms
- Check-engine light
- Reduced engine performance
- Exhaust sound or emissions may change
How to diagnose it
- Read freeze-frame data and valve B position or adaptation status to confirm that the learned-position data is missing.
- Check whether the code appeared after a battery disconnect, control-module reset, or exhaust valve B replacement.
- Inspect valve B’s actuator, linkage, connector, and wiring for binding, damage, or a loose connection.
- Use a scan tool to run the manufacturer’s valve B position-learn procedure and check whether adaptation completes.
- If learning fails, test valve B movement and its position feedback using the manufacturer’s diagnostic procedure.
Common fixes
- Complete the manufacturer’s position-learn procedure for exhaust flow control valve B.
- Free a sticking valve B linkage or clear an obstruction affecting its travel.
- Repair damaged wiring or reconnect a loose valve B connector.
- Replace valve B or its actuator if it cannot move or provide reliable position feedback during learning.
Can I keep driving?
If the vehicle runs normally, short, light-load driving is generally reasonable, but avoid demanding acceleration if performance or exhaust behaviour has changed. Arrange diagnosis if the warning persists or drivability worsens.
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.