P0048

Turbocharger/Supercharger Boost Control A Circuit High

P0048 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Boost Control A Circuit High. 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
P0048
Group
Powertrain
System
Turbo/Boost
Severity
Critical (limp mode / no-start)
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What P0048 means

P0048 is stored when the PCM detects that voltage on the boost control actuator 'A' circuit is stuck above the expected upper limit — the electrical opposite of P0047. The most common physical cause is a short to battery voltage somewhere in the control wire or solenoid harness, which saturates the PCM's output driver and prevents it from modulating the actuator. On some platforms the PCM driver transistor itself can fail in an always-on state, producing the same high-voltage condition. Because the PCM cannot pull the circuit low to vary duty cycle, the boost control actuator receives a constant full-on or full-off signal regardless of driving demand.

The consequence of a stuck-high signal depends heavily on the actuator design. On vacuum-solenoid VGT systems, a permanently energised solenoid typically holds the vacuum line open, driving the turbo vanes toward the maximum-boost position — this can cause dangerous over-boost and associated detonation, especially under hard acceleration. On modern electric VGT actuators (Garrett, Hella), the stuck signal may lock vanes at a fixed high-boost angle. In either case the PCM cannot close the control loop, leading to erratic or uncontrolled boost that can exceed safe limits before the over-boost protection (P0234) triggers.

P0048 should be treated as a high-priority fault. Uncontrolled over-boost risks piston damage, head gasket failure, and catastrophic turbocharger failure. The PCM activates limp mode when this code is detected, but limp mode may not fully prevent over-boost on all platforms. The vehicle should not be driven under load until the short is located and repaired.

Common causes

Most-frequently reported root causes when P0048 is logged.

  • 1
    Short to battery voltage in the PCM control wire between the PCM output pin and the boost control solenoid connector.
  • 2
    Failed PCM driver transistor stuck in the fully-on state, holding the circuit at supply voltage permanently.
  • 3
    Faulty boost control solenoid with an internal winding failure that draws the circuit high through a back-feed path.
  • 4
    Chafed wiring contacting a 12 V supply rail (battery feed, alternator wire, or ignition-switched power line).
  • 5
    Corroded or bridged connector pins causing a power wire to contact the signal wire inside the connector body.
  • 6
    Faulty boost pressure or turbocharger position sensor feeding incorrect high readings that the PCM misinterprets as a control circuit fault.
  • 7
    Vacuum system over-pressure on vacuum-solenoid platforms holding the actuator in the maximum-boost position independently of the solenoid.

Symptoms drivers notice

Check engine light illuminated; possible companion over-boost code P0234.
Over-boost under acceleration, potentially accompanied by detonation knock or rattling from the engine.
Engine entering limp mode with erratic power delivery — may surge at low throttle openings then cut power abruptly.
Black or blue exhaust smoke if the overly rich mixture from uncontrolled over-boost is not fully combusted.
Possible no-start condition if the PCM disables fuelling entirely as an over-boost protection measure.

How to diagnose P0048

A typical diagnostic flow when this code is present.

  1. 1
    Record freeze-frame and all stored codes; pay close attention to P0234 (over-boost) which often coexists with P0048.
  2. 2
    With ignition on and engine off, back-probe the PCM boost control signal wire at the solenoid connector — a reading at or near battery voltage when the solenoid is not commanded confirms a short to power.
  3. 3
    Disconnect the solenoid connector; if the wire voltage drops to normal, the short is in the harness between connector and solenoid (or the solenoid itself is back-feeding).
  4. 4
    If voltage remains high with the solenoid disconnected, trace the control wire from the solenoid connector back to the PCM for any contact with 12 V wiring — inspect particularly at brackets, heat shields, and harness looms.
  5. 5
    Measure solenoid resistance; an unusually low reading combined with a back-feed voltage suggests an internal solenoid fault.
  6. 6
    Inspect the VGT actuator and vacuum lines for mechanical over-boost conditions independent of the solenoid (split vacuum reservoir, stuck vacuum regulator) that could falsely implicate the control circuit.
  7. 7
    Only after all wiring, connector, and solenoid checks are clear should PCM driver failure be considered; verify with manufacturer-specific diagnostic procedure before replacement.

Related powertrain codes

Frequently asked questions

Is P0048 dangerous to drive with?

Yes. A circuit-high fault on the boost control output risks holding the VGT vanes or wastegate in a position that produces uncontrolled over-boost. This can cause detonation, piston damage, and turbo failure within a short drive. The vehicle should be moved to a workshop rather than driven under normal conditions.

Can P0048 cause a no-start?

On some platforms the PCM monitors boost control circuit integrity as part of the pre-start self-check and will inhibit fuelling if it detects a critical circuit fault. More commonly, the engine starts but immediately enters a very restrictive limp mode. Check manufacturer-specific documentation for your platform.

How do I distinguish P0048 (circuit high) from an actual mechanical over-boost?

Mechanical over-boost (e.g. from a faulty wastegate or split actuator hose) stores P0234 without necessarily triggering P0048. When P0048 appears, the PCM has detected an abnormal voltage on its own output driver circuit, pointing to an electrical fault. Both can coexist if the mechanical over-boost then overwhelms the PCM's ability to correct via the now-stuck actuator.

Which vehicles are most commonly affected by P0048?

Any turbocharged vehicle with an electronically controlled boost actuator can set this code, but it appears frequently on VW/Audi 2.0 TDI (N75 solenoid wiring failures), BMW N47 and N57 with Hella electric VGT actuators, Ford 6.0 and 6.7 Power Stroke (VGT solenoid harness), and Cummins ISB/ISL engines with a VGT solenoid circuit exposed to engine heat.

Disabling P0048 in software

RaceTune can permanently disable P0048 — 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.

ECUs with a P0048 disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C56 verified 1 software version
  • Bosch EDC17CP09 verified 1 software version

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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