P004B
Turbocharger/Supercharger Boost Control B Circuit Range/Performance
Turbo / boost control
Generic OBD-II
High
What it means
P004B means the ECM sees the "B" boost-control circuit performing outside its expected range — actual boost doesn't match what's commanded. It usually points to a sticking wastegate or actuator, a boost-control solenoid or sensor problem, or a boost leak in the intercooler plumbing. The engine keeps running but often loses power and may enter limp mode.
High
Can I keep driving? Drivable but often in reduced-power mode; avoid hard acceleration until the boost-control fault is fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Noticeable loss of power and weak acceleration
- Boost higher or lower than commanded (over/underboost)
- Possible reduced-power (limp) mode
Common causes
Most likely first
- Sticking wastegate or boost-control actuatorLikely
- Faulty boost-control solenoid or its wiring/connectorCommon
- Boost-pressure sensor out of range or driftingCommon
- Boost leaks — loose intercooler piping, split hoses, or a leaking intake connectionLess often
- Restricted air filter or intakeLess often
- Turbocharger wear (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and compare commanded vs. actual boost on a scan tool.
- Inspect intercooler piping, hoses, and clamps for boost leaks; check the air filter.
- Check the wastegate/actuator for free movement and correct operation.
- Test the boost-control solenoid and boost-pressure sensor wiring and resistance against spec.
- Repair or replace the failed component, clear the code, and road-test under boost.
FAQ
Quick answers
Is it safe to drive with P004B?+
You can drive gently, but overboost or a stuck wastegate can damage the turbo and engine over time, so don't put it off.
Can I just clear P004B?+
It will return once the ECM sees boost out of range again. Fix the underlying boost-control or leak problem first.
Related codes
Often seen with P004B
Read & clear P004B yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX