P004A Code- Turbocharger/Supercharger Boost Control 'B' Circuit/Open

What Does Code P004A Mean

The P004A code is a generic OBD-II trouble code that notes a problem with the boost control in the “A” circuit for the turbocharger or the supercharger. In this case the “A” stands for a specific chamber in the turbocharger or supercharger, as opposed to an individual component. The turbocharger or supercharger sends boost level information to the powertrain control module (PCM) via sensor input voltage signals. When these signals tell the PCM that the boost level is notably lower or higher than the manufacturer’s suggested settings, then the PCM cannot properly command the boost levels, and the P004A code will be triggered. In general, this will occur when the boost level is less than nine pounds, or more than 14 pounds.

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Possible symptoms

• Engine Light ON (or Service Engine Soon Warning Light)

Possible causes

• Faulty boost pressure/ turbocharger position sensor
• Boost pressure/ turbocharger position sensor harness is open or shorted
• Boost pressure/ turbocharger position sensor circuit poor electrical connection
• Faulty turbocharger/supercharger

Diagnostic and Repair Procedures

Begin by visually inspecting the turbo and turbo control system. Look for loose connections, damaged wiring, vacuum leaks etc. Next, check for technical service bulletins (TSBs) regarding the issue. If nothing is found, you will need to move forward to step by step diagnosis of the system.

The following is a generalized procedure, as testing for this code varies between vehicles. To accurately test the system, you'll want referred to the manufacturer's diagnostic flow chart.

Check system function by commanding the control solenoid to change position using a bidirectional scan tool. Raise the engine RPMS to about 1,200 RPMs and toggle the solenoid between on and off. While doing this, engine RPMs should change and the sensor position PID on the scan tool should change as well. If the RPMs fluctuates but the position/pressure PID does not change, suspect a problem with the sensor or its circuit. If RPMS do not change at all, suspect a problem with the control solenoid, turbo/supercharger or wiring.

• To check the circuit: test for power and ground at the solenoid. Note: the solenoid should be commanded on with a scan tool while making these checks. If either power or ground are lacking, you'll need to trace the factory wiring diagram to determine why.
• Check the turbocharger/supercharger: remove the intake to check the turbo/supercharger for damage or debris. If damage is found, replace the unit.
• Test the position/pressure sensor and circuit: in most cases, the position sensor should have three wires going to it: power, ground and signal. Test that all three are present.
• Test the control solenoid: in some cases, you may be able to test the solenoid by checking its' internal resistance with an ohmmeter. Consult the factory repair information for details. You may also be able to jump the solenoid to power and ground to see if it is operational.