Technical Description of OBD-II Trouble Code
Turbocharger/Supercharger Boost Control “A” Circuit Low
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code, which means it applies to OBD-II equipped vehicles that have a supercharger or turbocharger (Toyota, Hyundai, Ford Powerstroke, GMC Chevy Duramax, VW, Kia, 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 air pumps that force 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). This type of turbocharger has adjustable vanes located around the outside of the turbine, which can be opened and closed to vary the amount of boost pressure. This allows the turbocharger to be controlled independently of engine speed. The position of the vanes is controlled by the powertrain control module (PCM), typically using an electronic control solenoid or motor. The turbo vane position is determined using a dedicated position sensor.
In vehicles that use a traditional fixed displacement turbocharger or supercharger, boost is controlled through 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 “A” indicates a problem with a portion of the system circuit, rather than a specific symptom or component.
Code P0047 is set when the PCM detects a low boost control solenoid signal, regardless of whether the engine uses a VGT turbo or a traditional turbocharger/supercharger.
One style of turbocharger boost control solenoid valve:
Related turbo/supercharger engine trouble codes:
Code Severity & Symptoms
The severity of these codes ranges from moderate to severe. In some cases, problems with the turbocharger/supercharger can lead to severe engine damage. It is advisable to address this code as soon as possible.
Symptoms of a P0047 code may include:
Causes
Potential causes for this code to be set 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 technical service bulletins (TSBs) regarding the issue. If nothing is found, you will need to proceed with 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 should 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 RPMs to about 1,200 RPMs and toggle the solenoid between on and off. While doing this, the engine RPMs should change and the sensor position PID on the scan tool should also change. If the RPMs fluctuate but the position/pressure PID does not change, suspect a problem with the sensor or its circuit. If the RPMs do not change at all, suspect a problem with the control solenoid, turbo/supercharger, or wiring.
