P26F1

Turbocharger Boost Control B Circuit High

P26F1 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger Boost Control B Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P26F1
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P26F1 means

P26F1 is set when the ECM detects a high voltage condition on the control circuit for turbocharger boost control system B. This circuit is used to drive the boost control solenoid or electronic actuator for the secondary turbocharger or bank B of a twin-turbo system. The ECM monitors the feedback or command signal voltage and stores this code when the measured value exceeds the maximum calibrated threshold.

The most common electrical causes are a short to the vehicle supply voltage on the signal or control wire, an open in the circuit that allows the signal to float high, or an internal failure within the boost control actuator or solenoid itself. The ECM uses this signal to modulate turbocharger output, so a circuit fault in the high direction may result in an actuator that is stuck or unable to respond to commands.

Boost control failure can lead to overboost or underboost conditions depending on the actuator's default fail-safe position. The ECM will typically set a performance fault or limit boost via alternative strategies while P26F1 is active. Electrical diagnosis using a wiring diagram is essential to isolate the fault location before replacing components.

Common causes

Most-frequently reported root causes when P26F1 is logged.

  • 1
    Short to supply voltage on the boost control solenoid circuit B signal wire.
  • 2
    Open circuit in the boost control actuator circuit allowing the signal to float high.
  • 3
    Failed boost control solenoid or actuator with an internal electrical fault.
  • 4
    Damaged wiring harness near heat sources in the turbocharger area.
  • 5
    Corroded or contaminated connector at the boost control actuator for system B.
  • 6
    ECM output driver fault causing an incorrect high output on the control circuit.

Symptoms drivers notice

MIL illuminated with possible boost or engine warning.
Possible overboost or underboost condition depending on actuator default position.
Reduced engine power or limp mode active.
Inconsistent or erratic turbocharger response.
Possible audible turbo abnormality under load.

How to diagnose P26F1

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note any related turbocharger or boost solenoid codes.
  2. 2
    Locate the boost control solenoid or actuator for system B using the vehicle wiring diagram.
  3. 3
    With the connector unplugged, measure the voltage on the control circuit wire at the harness side; presence of supply voltage indicates a short to power.
  4. 4
    Measure the resistance of the boost control solenoid across its terminals; compare to specification.
  5. 5
    Inspect the wiring harness in the turbocharger area for heat damage, chafing, or contact with metal edges.
  6. 6
    Reconnect the harness and use a scan tool to command the solenoid; observe whether the circuit voltage behaves correctly.
  7. 7
    Replace the faulty solenoid or repair the wiring as indicated, clear codes, and road test to confirm the repair.

Vehicles where we've handled P26F1

Platforms in our catalogue with confirmed P26F1 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can P26F1 cause the turbo to produce too much boost?

Potentially yes. If the actuator defaults to a fully open position when it loses proper control signal, boost may be unregulated and exceed targets until the ECM intervenes with fuel cuts or limiting strategies.

Is the boost control solenoid expensive to replace?

Boost solenoids are typically moderate-cost components. Labor varies depending on accessibility in the engine bay. Always confirm the solenoid is actually faulty before replacement.

How is P26F1 different from P26EE?

P26F1 is an electrical circuit fault (signal voltage too high), while P26EE is a performance fault (actual boost not matching target). They can occur together but have different root causes.

Will cleaning the boost solenoid fix this code?

P26F1 is an electrical fault, not a mechanical sticking issue, so cleaning is unlikely to resolve it. Focus on wiring, connectors, and the solenoid's electrical condition.

Disabling P26F1 in software

RaceTune can permanently disable P26F1 — 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 P26F1 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 EDC17C50 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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