P004A
Turbocharger/Supercharger Boost Control B Circuit/Open
Turbocharger / boost control
Generic OBD-II
High
What it means
P004A means the ECM has detected an open (broken) electrical connection in the "B" turbocharger/supercharger boost-control circuit. With the circuit open the ECM can't command the boost-control solenoid, so it defaults to minimum boost or limp mode to protect the engine. The usual causes are a broken wire, a bad connector, or a failed solenoid coil — so you'll notice reduced power rather than a no-start.
High
Can I keep driving? Reduced — with the boost-control circuit open the ECM usually forces minimum boost or limp mode; you can limp home but power will be well down.
Common symptoms
What you'll notice
- Check-engine light on
- Noticeable loss of power / limp mode
- Little or no boost from the turbo/supercharger
- No boost response when you press the pedal
Common causes
Most likely first
- Open (broken) wire in the 'B' boost-control circuitLikely
- Disconnected, corroded, or damaged boost-control solenoid connectorCommon
- Failed boost-control solenoid with an open coil windingCommon
- Chafed or cut harness between the solenoid and the ECMLess often
- Faulty ECM boost-control driver (rare — rule out wiring first)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data to confirm when the open is detected (usually as soon as boost is commanded).
- Inspect the boost-control solenoid connector for backed-out pins, corrosion, or a loose fit.
- Measure the solenoid coil resistance — an open (infinite) reading means the solenoid is bad.
- Check continuity of the control and feed wires back to the ECM; repair any open or chafed section.
- If wiring and solenoid are good, suspect the ECM driver; clear the code and re-test after any repair.
FAQ
Quick answers
Is it safe to drive with P004A?+
Briefly and gently. The engine will limit boost, so it's down on power — get the boost-control circuit repaired before driving normally.
Can I just clear P004A?+
It comes straight back while the circuit is open. The broken wire, connector, or solenoid has to be fixed first.
Related codes
Often seen with P004A
Read & clear P004A 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