What it means
During cold-start monitoring, the control module detects that boost control B is not performing as expected.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Boost control B regulates a separate boost-control channel or component during the monitored cold-start period; its exact hardware depends on the vehicle. The engine control module compares the commanded and measured response for B and sets this code when that channel does not perform as expected while cold.
Common causes
Most likely first.
- Turbocharger or supercharger boost actuator sticking when cold
- Boost control valve or solenoid fault
- Vacuum hose leak or restriction, if fitted
- Wiring or connector fault affecting boost control
Symptoms
- Check-engine light may come on
- Reduced power or poor acceleration, especially during cold start
How to diagnose it
- Read freeze-frame data and note coolant temperature, load, and boost readings to establish whether the fault occurred during cold-start monitoring.
- Use a scan tool on a cold engine to compare commanded and actual boost-control B operation under the manufacturer's test conditions.
- Inspect the B actuator, valve or solenoid, connector, and harness specifically for sticking, damage, or corrosion.
- If vacuum-operated, inspect the hoses serving boost control B for leaks, kinks, disconnection, or restriction.
- Test the B circuit, actuator movement, and boost response against the manufacturer's specification before suspecting the turbocharger or supercharger itself.
Common fixes
- Reconnect a loose boost-control B connector or secure a disconnected hose.
- Repair a leaking, kinked, or restricted vacuum hose if fitted.
- Repair damaged wiring or corroded terminals in the B control circuit.
- Replace a faulty boost-control B solenoid or valve.
- Repair or replace a sticking B actuator or other confirmed mechanical boost-control fault.
Can I keep driving?
If power is reduced, avoid hard acceleration, towing, and situations that require rapid merging until the cold-start boost fault is diagnosed. Stop driving if the engine develops severe power loss, unusual turbo noise, or other signs of a serious mechanical problem.
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.