P004C
Turbocharger/Supercharger Boost Control B Circuit Low
Turbo / boost control
Generic OBD-II
High
What it means
P004C is an electrical fault: the ECM sees low voltage (a short to ground or open) in the "B" turbocharger/supercharger boost-control circuit — the solenoid or actuator that regulates boost. It's a wiring or actuator problem rather than a mechanical turbo failure. The car usually still runs but often falls into reduced-power mode with weak boost until the circuit is fixed.
High
Can I keep driving? Drivable but sluggish — a boost-control circuit fault often drops the engine into reduced-power or limp mode; expect weak acceleration until it's fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Noticeable loss of power / weak boost
- Reduced-power or limp mode
- Hesitation under acceleration
Common causes
Most likely first
- Short to ground or open in the boost-control 'B' actuator/solenoid circuitLikely
- Failed boost-control solenoid or electronic wastegate actuatorCommon
- Corroded, loose, or damaged connector at the actuatorCommon
- Chafed or pinched wiring in the control circuitLess often
- Faulty ECM output driver (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the code names the 'B' boost-control circuit.
- Inspect the boost-control solenoid/actuator connector and wiring for damage, heat, or corrosion.
- Measure the solenoid/actuator resistance and compare to spec.
- Check the control wire for a short to ground or an open back to the ECM, and verify its supply voltage.
- Replace the boost-control solenoid or actuator if it fails testing.
- Clear the code, road-test, and confirm boost returns to normal.
FAQ
Quick answers
Is it safe to drive with P004C?+
You can limp home, but the car will likely be in reduced-power mode and boost is unreliable. Avoid hard acceleration and get it diagnosed soon.
Can I just clear P004C?+
It comes back as soon as the ECM commands boost and re-tests the circuit unless the wiring or actuator is repaired.
Related codes
Often seen with P004C
Read & clear P004C 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