What Does P004A Mean?
The PCM has detected an open circuit or malfunction in the turbocharger/supercharger boost control 'B' circuit. On vehicles with twin turbos or a two-stage boost control system, 'B' refers to the secondary boost control solenoid. This solenoid may control the secondary turbo wastegate, a variable geometry turbine, or a secondary boost bypass. The driver will notice reduced power and possibly limp mode.
Common Causes
35%
Failed boost control solenoid 'B' with open internal coil winding
30%
Broken, disconnected, or corroded wiring/connector to boost solenoid 'B'
20%
Cracked or disconnected vacuum/pressure lines to the secondary wastegate or VGT actuator
15%
PCM driver circuit failure for the boost solenoid 'B' output
Diagnostic Steps
1
Identify the boost control solenoid 'B' location — on twin-turbo systems it controls the secondary turbo wastegate; on variable geometry turbos it may control the VGT actuator.
2
Disconnect the solenoid 'B' connector and measure coil resistance — expect 10–30 ohms. Infinite resistance confirms an open coil.
3
With the solenoid disconnected and KOEO, verify battery voltage on the power supply pin and check continuity on the control wire back to the PCM (less than 1 ohm expected).
4
Inspect the connector and wiring for corrosion, heat damage, or broken pins, paying special attention to areas near exhaust components.
5
If electrical tests pass, use a bi-directional scan tool to command the solenoid on/off while monitoring its operation — listen for clicks and verify the associated actuator moves.
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
The PCM has detected an open circuit or malfunction in the turbocharger/supercharger boost control 'B' circuit. On vehicles with twin turbos or a two-stage boost control system, 'B' refers to the secondary boost control solenoid. This solenoid may control the secondary turbo wastegate, a variable ge...
The most common cause of P004A (Turbocharger/Supercharger Boost Control "B" Circuit/Open) is: Failed boost control solenoid 'B' with open internal coil winding
Typical repair costs for P004A range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution and avoid heavy loads. Loss of the secondary boost control may result in reduced power or the vehicle defaulting to a single-turbo mode. The vehicle should still be driveable but with reduced performance. Avoid sustained high-boost driving until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P004A to identify the root cause.
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Quick Info
Category
Powertrain
System
Forced Induction / Turbocharger
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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