P27A8

Turbocharger Boost Control A Circuit High

P27A8 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger Boost Control A 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
P27A8
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P27A8 means

P27A8 is stored by the ECM or PCM when the voltage measured on the turbocharger boost control solenoid A circuit is higher than expected. The boost control solenoid (also known as the wastegate control solenoid or boost pressure regulator) modulates the boost pressure delivered by the turbocharger by bleeding off or applying pressure to the wastegate actuator. A high-circuit condition typically indicates an open circuit in the solenoid winding, a short to battery voltage on the control wire, or a loss of ground reference.

When this fault is active the ECM cannot accurately control boost pressure. As a protective measure most calibrations reduce boost to a safe default level or enter a throttle-limiting strategy to prevent engine damage from uncontrolled boost. Symptoms include noticeably reduced power and possible overboost or underboost depending on the wastegate default position.

Diagnosis should begin with harness and connector inspection, followed by resistance measurement of the solenoid. An open-circuit solenoid or a broken wire is the most common finding. The ECM itself is an unlikely cause but should be evaluated last after ruling out all wiring and solenoid faults.

Common causes

Most-frequently reported root causes when P27A8 is logged.

  • 1
    Open circuit in the boost control solenoid A winding.
  • 2
    Broken or disconnected wire between the ECM and the solenoid.
  • 3
    Short to battery voltage on the solenoid control signal wire.
  • 4
    Corroded or damaged solenoid connector causing loss of continuity.
  • 5
    Faulty ECM boost control driver with high-impedance output.
  • 6
    Damaged wiring harness in the high-heat environment near the turbocharger.
  • 7
    Improper wiring repair introducing high resistance or open circuit.

Symptoms drivers notice

MIL illuminated.
Noticeably reduced engine power and acceleration.
Possible overboost condition if the wastegate defaults closed.
Possible underboost condition if the wastegate defaults open.
Engine entering a boost-limited or throttle-limited protective strategy.

How to diagnose P27A8

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, retrieve all DTCs, and review boost pressure actual versus requested PIDs.
  2. 2
    Inspect the boost control solenoid connector and wiring harness in the turbocharger area for heat damage or corrosion.
  3. 3
    Measure boost control solenoid A resistance at the solenoid connector and compare to specification.
  4. 4
    With the ECM connector unplugged, check for short to battery voltage on the solenoid control wire.
  5. 5
    Verify ground integrity for the solenoid and ECM.
  6. 6
    Command the solenoid on and off using bidirectional scan tool controls and observe boost pressure response.
  7. 7
    Replace the solenoid or repair the wiring as indicated; evaluate the ECM only after all external circuit checks pass.

Related powertrain codes

Frequently asked questions

Will P27A8 cause the engine to overboost?

It depends on the wastegate actuator default position. If the wastegate defaults closed with no control signal, boost can build unchecked. If it defaults open, boost will be low.

Is P27A8 specific to one type of turbocharger?

No. The code applies to any turbocharged engine that uses an electrically controlled boost solenoid on circuit A, regardless of turbocharger design.

Can heat damage cause P27A8?

Yes. The boost control solenoid and its wiring are located near the hot side of the turbocharger. Heat-induced insulation breakdown and connector corrosion are common causes.

Is P27A8 dangerous to ignore?

Yes. Uncontrolled boost pressure can cause engine damage including detonation, blown intercooler piping, or head gasket failure. The fault should be repaired promptly.

Disabling P27A8 in software

RaceTune can permanently disable P27A8 — 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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