Technical Description of OBD-II Trouble Code
Turbocharger/Supercharger Boost Control “B” Circuit High
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles with a supercharger or turbocharger (Toyota, GMC Chevrolet Duramax, Mazda, Chrysler, Jeep, Ford Powerstroke, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Turbochargers and superchargers are devices that pump air into the engine to increase power. Superchargers are driven by a belt connected to the engine crankshaft, while turbochargers are driven by the engine’s exhaust.
Many modern turbocharged vehicles use a variable geometry turbocharger (VGT), which has adjustable vanes located around the turbine. These vanes can be opened and closed to control the amount of boost pressure. This allows the turbo to be controlled independently of engine speed. The position of the vanes is controlled by the powertrain control module (PCM) using an electronic control solenoid or motor. A dedicated position sensor is used to determine the turbo vane position.
In vehicles with a traditional fixed displacement turbocharger or supercharger, boost is controlled using a wastegate or bypass valve. This valve opens to release excess boost pressure. The PCM monitors this system using a boost pressure sensor.
In the context of this trouble code, the “B” indicates a problem with a portion of the system circuit, rather than a specific symptom or component.
Code P004D is triggered when the PCM detects a high boost control solenoid signal, regardless of whether the engine uses a VGT turbo or a traditional turbocharger/supercharger.
Other related turbo/supercharger engine trouble codes include:
Code Severity & Symptoms
These codes have a moderate to severe severity level. In some cases, issues with the turbocharger/supercharger can cause significant engine damage. It is advisable to address this code as soon as possible.
Symptoms of a P004D code may include:
Causes
Possible causes for this code to be triggered are:
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 any technical service bulletins (TSBs) related to the issue. If no relevant information is found, proceed with a step-by-step diagnosis of the system.
The following is a general procedure, as testing for this code can vary between vehicles. To accurately test the system, refer to the manufacturer’s diagnostic flow chart.
Check the system function by commanding the control solenoid to change position using a bidirectional scan tool. Raise the engine RPM to about 1,200 RPM and toggle the solenoid between on and off. While doing this, the engine RPM should change and the sensor position PID on the scan tool should also change. If the RPM fluctuates but the position/pressure PID does not change, suspect a problem with the sensor or its circuit. If the RPM does not change at all, suspect a problem with the control solenoid, turbo/supercharger, or wiring.
