What it means
The control module monitors whether coolant bypass valve B remains closed when its operating conditions require it. It sets this code when the valve is detected as stuck closed, restricting coolant flow through the bypass path.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Coolant bypass valve B controls coolant flow through the bypass path under commands from the engine control module. This code means valve B is detected as stuck closed when operating conditions call for bypass flow, which can slow warm-up and reduce cabin heat.
Common causes
Most likely first.
- Valve seized closed by debris
- Actuator linkage jammed in closed position
- Carbon or debris buildup preventing free movement
Symptoms
- Check-engine light
- Engine may take longer to warm up
- Cabin heat may be reduced
How to diagnose it
- Check freeze-frame data and live coolant-temperature readings to see whether the engine is taking too long to warm up.
- With the engine cool, inspect bypass valve B and its linkage for debris or a jammed closed position.
- Inspect valve B's connector and wiring for looseness, corrosion, or damage.
- Command valve B through its available positions with a scan tool and check for movement and a corresponding temperature response.
- Check for debris or carbon buildup restricting valve B, then test its actuator and control circuit to the manufacturer's specification.
Common fixes
- Remove debris restricting bypass valve B.
- Repair damaged wiring or connector contacts at valve B.
- Free or repair valve B's linkage if it is jammed closed.
- Replace valve B if it remains stuck closed after cleaning or linkage repair.
Can I keep driving?
Gentle driving may be possible if the temperature gauge stays normal, but allow extra warm-up time and monitor temperature closely. Stop if the engine overheats; restricted bypass flow can worsen temperature control and leave the cabin with reduced 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.