What it means
The engine coolant bypass valve B position sensor signal drops out or jumps intermittently. Loose connector or noisy ground.
At a glance
- Usually lights the check-engine light
How it works
Coolant bypass valve B redirects coolant to help manage engine warm-up and temperature, and its position sensor reports how far the valve has moved. This code sets when that signal repeatedly drops out or jumps instead of changing smoothly, pointing to an intermittent sensor, connector, wiring, or ground problem.
Common causes
Most likely first.
- Intermittent wiring or connector fault
- Intermittent sensor fault
- Poor ground connection
Symptoms
- Check-engine light on
- Intermittent coolant temperature fluctuations
- Intermittent changes in cabin heat
How to diagnose it
- Save freeze-frame data and review live valve B command, reported position, and coolant temperature to identify when the signal becomes erratic.
- Inspect valve B's connector, harness, and ground for looseness, corrosion, chafing, or strain, especially where movement or heat could disturb the connection.
- With live data displayed, gently flex the harness and connector to see whether the reported position glitches when the fault is reproduced.
- Check the sensor ground and signal connections for intermittent continuity or excessive resistance, following the wiring diagram and manufacturer's specification.
- If the wiring remains stable, test valve B's position sensor and valve movement for intermittent faults before replacing the failed part.
Common fixes
- Secure the valve B connector and repair damaged or chafed wiring.
- Clean and restore a poor sensor ground or corroded terminal.
- Replace a position sensor that drops out intermittently.
- Replace or repair the bypass valve B assembly if its sensor or linkage is not serviceable separately.
Can I keep driving?
Driving may be reasonable for a short distance if coolant temperature stays normal, but monitor the gauge and avoid a long trip until the intermittent fault is found. Stop if the engine overheats or cabin heat changes alongside an abnormal temperature reading.
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.