P0045

Turbocharger/Supercharger Boost Control A Circuit/Open

P0045 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Boost Control A Circuit/Open. 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
P0045
Group
Powertrain
System
Turbo/Boost
Severity
Warning (MIL on, possible limp mode)
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What P0045 means

P0045 is set when the PCM detects an open circuit in the boost control 'A' actuator circuit — the output path that drives the wastegate solenoid, VGT vacuum solenoid, or electric VGT actuator responsible for regulating turbocharger boost pressure. On vacuum-controlled platforms such as VW/Audi 2.0 TDI with a VNT (variable-nozzle turbine), this solenoid modulates manifold vacuum to the turbo actuator; on modern systems like BMW N47/N57 or Garrett GTB/VNT with electronic actuators, the PCM drives a DC motor or stepper directly. In either case, an open circuit means the PCM's commanded signal cannot reach the actuator.

The most common physical causes are a broken wire or severely corroded connector pin in the harness between the PCM and the solenoid or actuator. Internal failure of the solenoid coil (open winding) produces the same open-circuit reading. Because the actuator defaults to a fixed position when signal is lost, the turbocharger cannot vary its geometry or wastegate position in response to load, resulting in either permanent under-boost or over-boost depending on the actuator's mechanical fail-safe position.

P0045 is typically a moderate-to-severe fault. The check engine light illuminates and significant power loss is common. On VGT diesels in particular, a stuck-open vane position causes severe under-boost and heavy black smoke under acceleration. Prompt diagnosis is recommended to prevent turbo damage from running the vane mechanism in a fixed position under varying thermal and pressure cycles.

Common causes

Most-frequently reported root causes when P0045 is logged.

  • 1
    Broken or open wire in the harness between the PCM boost control output pin and the solenoid or actuator connector.
  • 2
    Severely corroded, backed-out, or melted connector pin at the boost control solenoid or VGT actuator.
  • 3
    Internally open solenoid coil (measured infinite resistance) due to thermal fatigue or vibration damage.
  • 4
    Blown fuse or open relay in the solenoid supply circuit on platforms that power the solenoid via a dedicated fuse.
  • 5
    Failed PCM driver output unable to source or sink current on the boost control channel.
  • 6
    Vacuum line collapse or disconnection (vacuum-solenoid platforms) causing no actuation even when the solenoid functions electrically.
  • 7
    Faulty turbocharger position sensor causing the PCM to misread actuator feedback and log an open-circuit fault.

Symptoms drivers notice

Check engine light illuminated with significant reduction in engine power.
Marked under-boost throughout the RPM range; turbo whistle is weak or absent under load.
Heavy black or grey smoke during acceleration on diesel applications with VGT stuck in high-flow position.
Sluggish acceleration and inability to reach normal highway speeds without excessive throttle.
Poor fuel economy due to the ECU enriching mixture to compensate for reduced airflow feedback.
Possible over-boost and associated detonation if the actuator defaults to a fully closed (high-boost) position.

How to diagnose P0045

A typical diagnostic flow when this code is present.

  1. 1
    Record freeze-frame data and check for companion codes (P0046, P0299 under-boost, P0234 over-boost) to narrow down system state.
  2. 2
    Inspect the boost control solenoid and VGT actuator harness for broken wires, melted insulation, and corroded connector pins.
  3. 3
    With ignition on, verify supply voltage at the solenoid connector; absence of supply voltage points to a blown fuse or open relay upstream.
  4. 4
    Measure solenoid coil resistance; an open reading (OL on a multimeter) confirms internal winding failure requiring solenoid replacement.
  5. 5
    Check the PCM control wire for continuity from connector to PCM pin using a wiring diagram; any open section must be repaired.
  6. 6
    Using a bidirectional scan tool, command the boost control solenoid to full duty cycle at idle and verify audible click and actuator movement.
  7. 7
    If all wiring and solenoid checks pass, inspect for collapsed vacuum lines (vacuum-solenoid systems) or a seized VGT vane mechanism before suspecting PCM failure.

Related powertrain codes

Frequently asked questions

What happens to boost pressure when P0045 is active?

It depends on the actuator's mechanical fail-safe position. Most VGT designs default to a partially open vane position producing low boost; some wastegate designs spring to fully open, eliminating boost almost entirely. In rare cases the actuator sticks closed, causing over-boost.

Is P0045 specific to one brand or engine?

No, it is a generic SAE code that applies to any turbocharged or supercharged OBD-II vehicle. Common platforms include VW/Audi 2.0 TDI (N75 solenoid circuit), BMW N47/N57 (electric VGT actuator), Ford 6.0/6.7 Power Stroke, and Cummins ISB/ISL engines.

Can a vacuum leak trigger P0045 on a diesel?

Yes. On vacuum-controlled VNT systems the PCM monitors actuator position feedback. If a vacuum line to the turbo actuator is split or disconnected the actuator never moves, the position sensor reports no change, and the PCM may log P0045 alongside a position rationality fault.

Will replacing the solenoid always fix P0045?

Not always. If the solenoid tests open it must be replaced, but if the solenoid measures correctly the fault is in the wiring, connector, or PCM driver. Replacing the solenoid without verifying wiring continuity and connector integrity first is a common and costly mis-step.

Disabling P0045 in software

RaceTune can permanently disable P0045 — 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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