What it means
Voltage on the engine coolant bypass valve B position sensor signal line is above the expected window. Wire shorted to B+ or sensor open.
At a glance
- Usually lights the check-engine light
How it works
Coolant bypass valve B redirects coolant between engine passages to help control warm-up and temperature. The module compares valve B's position signal with the range expected for its commanded position; this code sets when the signal is consistently too high, such as from a short to power, an open circuit, or a failed sensor.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open or high-resistance signal/ground circuit
- Sensor fault
Symptoms
- Check-engine light on
- Coolant temperature fluctuations
- Longer warm-up or reduced cabin heat
How to diagnose it
- Record freeze-frame data and compare valve B's commanded and reported positions with coolant temperature to see when the high reading occurs.
- With the engine cool, inspect valve B's connector and the signal, power, and ground wiring for corrosion, damage, or contact with a power feed.
- Use live data while gently moving the harness to check whether valve B's position signal stays high or changes with connector movement.
- Following the wiring diagram, check the signal circuit for a short to power and check for an open or excessive resistance in the signal and ground paths.
- If wiring and connections pass, test valve B's position sensor and actuator against the manufacturer's specification and replace the faulty component.
Common fixes
- Repair a loose, corroded, or damaged valve B connector or wire.
- Restore an open or high-resistance sensor ground or signal connection.
- Repair a signal wire shorted to a power feed.
- Replace the faulty coolant bypass valve B position sensor or valve assembly if the sensor is not separately serviceable.
Can I keep driving?
A short, gentle drive may be possible if coolant temperature remains stable and there are no signs of overheating, but avoid long trips or heavy loads. Stop if the temperature rises abnormally; faulty bypass control can disrupt warm-up and 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.