P0047

Turbocharger/Supercharger Boost Control A Circuit Low

P0047 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Boost Control A Circuit Low. It is logged by the engine control unit when the turbo/boost monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0047
Group
Powertrain
System
Turbo/Boost
Severity
Warning (MIL on, possible limp mode)
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What P0047 means

P0047 is stored when the PCM detects that the voltage on the boost control actuator 'A' circuit is stuck below the minimum expected threshold — typically a short to ground or an open PCM driver that the ECU reads as a near-zero signal. The boost control actuator circuit drives the solenoid that positions the VGT vanes or commands the wastegate, and a sustained low-voltage condition means the PCM cannot deliver an effective control signal to increase or decrease boost. The ECU detects the fault via its internal current-sense or voltage-feedback loop on the driver output.

On vacuum-solenoid platforms such as the VW/Audi 2.0 TDI (N75 solenoid), a circuit-low condition means the solenoid is receiving little or no drive current, which in most designs defaults the turbo vanes toward the fully open (low-boost) position. This causes severe under-boost, loss of power, and on diesel engines noticeable black smoke. On electric VGT actuator platforms (Garrett GTB series, Hella actuators used on BMW N47/N57, Cummins ISB/ISL), a stuck-low signal may force the actuator to a fixed failsafe position that the manufacturer has calibrated for safe running but with greatly reduced performance.

The code severity is moderate to high. The vehicle will typically enter limp mode with reduced boost. Prolonged operation risks excessive exhaust temperatures (turbo over-temperature from high exhaust backpressure on low-boost VGT), carbon accumulation, and eventual turbo bearing failure. The underlying electrical fault should be corrected before returning the vehicle to normal use.

Common causes

Most-frequently reported root causes when P0047 is logged.

  • 1
    Short to ground in the PCM control wire between the PCM output pin and the boost control solenoid or actuator.
  • 2
    Failed boost control solenoid with an internally shorted coil pulling the circuit voltage below threshold.
  • 3
    Corroded or water-damaged connector causing a low-resistance path to chassis ground.
  • 4
    Chafed or pinched wiring harness where the insulation has worn through against a metal bracket or exhaust component.
  • 5
    Blown fuse in the solenoid supply circuit forcing the control signal reference to collapse.
  • 6
    Failed PCM internal driver transistor that cannot switch the output high, leaving it in a low state.
  • 7
    Contaminated or seized VGT actuator providing excessive resistive load that collapses the drive voltage.

Symptoms drivers notice

Check engine light illuminated with noticeable loss of power and turbo response.
Engine entering limp mode with reduced boost pressure and a 'Reduced Power' dashboard message.
Heavy black smoke during acceleration on diesel engines with VGT stuck in high-exhaust-flow (low-boost) position.
Sluggish acceleration and failure to reach normal power output even at wide-open throttle.
Poor fuel economy as the ECU enriches fuel delivery to compensate for low airflow readings.
Irregular automatic transmission shifting triggered by the reduced torque output signal from the ECM.

How to diagnose P0047

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, record freeze-frame data and all stored codes; note companion codes such as P0299 (under-boost) or P0045.
  2. 2
    Inspect the boost control solenoid wiring harness and connector for chafing, corrosion, melted insulation, and pushed-back terminals.
  3. 3
    Verify fuse and relay integrity in the solenoid supply circuit with a multimeter.
  4. 4
    With ignition on and engine off, back-probe the PCM control wire at the solenoid connector; a reading near 0 V when the solenoid is commanded off (or when key-on with no command) confirms a short to ground — disconnect the solenoid to isolate whether the short is in the harness or the solenoid itself.
  5. 5
    Measure solenoid coil resistance; a very low reading (below 1 Ω) indicates an internal short requiring solenoid replacement.
  6. 6
    Test the control wire continuity from solenoid connector back to PCM pin; repair any grounded section found.
  7. 7
    Command the solenoid with a bidirectional scanner after repairs and confirm voltage transitions and actuator movement before clearing codes.

Related powertrain codes

Frequently asked questions

What is the default turbo position when P0047 is active?

It depends on the platform. On most vacuum-operated VNT/VGT systems the vanes spring toward the open (low-boost) position when drive signal is lost, resulting in severe under-boost. On some electric actuator systems (e.g. Hella on BMW N57) the actuator holds its last commanded position or moves to a calibrated safe position — both scenarios reduce available power.

Can a bad ground cause P0047 without any damaged wiring?

Yes. A high-resistance engine block ground or corroded battery negative terminal can lower the reference ground for the PCM driver circuit, making the control wire read low even if the wire itself is intact. Always inspect and clean all engine grounds before diagnosing upstream wiring or components.

Will P0047 appear on petrol turbos as well as diesels?

Yes, it is a generic SAE code applicable to any turbocharged or supercharged petrol or diesel engine. However, diesel engines with VGT turbos (VW TDI, BMW N47, Cummins, Ford Power Stroke) produce the most pronounced symptoms because they rely entirely on VGT geometry for boost control across a wide range.

How do I tell P0047 (circuit low) apart from P0045 (circuit open) during diagnosis?

Measure voltage on the control wire with the solenoid connector plugged in (key on, solenoid not commanded). P0047 typically shows near 0 V caused by a hard pull to ground; P0045 often shows an unexpected high or floating voltage because the circuit is open and unpowered. Disconnect the solenoid and re-measure: if voltage normalises, the short is in the solenoid itself.

Disabling P0047 in software

RaceTune can permanently disable P0047 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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