P004C Turbocharger/Supercharger Boost Control "B" Circuit Low Trouble Code

P004C Turbo/Supercharger Boost Control B Circuit Low

OBD-II Trouble Code Technical Description

Turbocharger/Supercharger Boost Control "B" Circuit Low

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles that have a supercharger or turbocharger (Toyota, Hyundai, Ford Powerstroke, GMC Chevy Duramax, VW, Kia, etc.). Although generic, the specific repair steps may vary depending on make/model.

Turbochargers and superchargers are air pumps that force air into the engine to increase power. Superchargers are driven off the engine crankshaft by a belt, whereas turbochargers are driven by the engine's exhaust.

 

Many modern turbocharged vehicles use what's referred to as a variable geometry turbocharger (VGT).This type of turbo has adjustable vanes located around the outside of the turbine that can be opened and closed to vary the amount of boost pressure. This allows the turbo to be controlled independent of engine speed. Generally, the vanes are open when the engine is under light load and open as load increases. Vane position is controlled by the powertrain control module (PCM), typically using an electronic control solenoid or motor. Turbo vane position is determined using a dedicated position sensor.

On vehicles that use a traditional, fixed displacement turbo charger or supercharger, boost is controlled via a wastegate or bypass valve. This valve opens to relieve boost pressure. The PCM monitors this system using a boost pressure sensor.

In reference to this trouble code, the "B" indicates the problem in with a portion of the system circuit, instead of a particular symptom or component.

Code P004C is set when the PCM detects a low boost control solenoid signal, no matter if the engine uses a VGT turbo or traditional turbocharger/supercharger.

Related turbo / supercharger engine trouble codes:

P004A Turbocharger/Supercharger Boost Control "B" Circuit/Open P004B Turbocharger/Supercharger Boost Control "B" Circuit Range/Performance P004D Turbocharger/Supercharger Boost Control "B" Circuit High P004F Turbocharger/Supercharger Boost Control "B" Circuit Intermittent

Code Severity & Symptoms

The severity of these codes is moderate to severe. In some cases, problems with the turbocharger/supercharger can lead to severe engine damage. It's a good idea to address this code as soon as possible.

Symptoms of a P004C code may include:

Insufficient boost resulting in lack of engine performance Illuminated check engine light

Causes

Potential causes for this code to set are:

Faulty boost pressure/ turbocharger position sensor Failed turbocharger/super charger Defective control solenoid Wiring problems Faulty PCM Vacuum leaks if the valve is vacuum controlled

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 w

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