P2C2B

Turbocharger/Supercharger Boost Control B Circuit Open

P2C2B is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Boost Control B Circuit Open. 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
P2C2B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P2C2B means

P2C2B indicates an open circuit fault detected in the boost control actuator B circuit. On engines equipped with two turbochargers or a dual-channel boost control system, circuit B controls the second actuator or the secondary channel of a twin-scroll system. The ECM expects to see normal operating current when it commands the actuator, and an open condition means no current is flowing.

Without proper control of the B-circuit actuator, the second stage of boost regulation is lost. Depending on the turbocharger system design, this may result in underboost, overboost on one bank, or asymmetric power delivery. The ECM typically defaults to a conservative boost strategy to prevent mechanical damage.

Diagnosis should follow the same systematic approach as P2C20 for circuit A. Wiring harness integrity, connector condition, actuator coil resistance, and ECM driver function all need to be verified in sequence. On twin-turbo applications, inspect the additional harness routing unique to the B-circuit actuator, which often follows a different path and may be exposed to different heat or vibration sources.

Common causes

Most-frequently reported root causes when P2C2B is logged.

  • 1
    Open or broken wire in the boost control B actuator feed or ground circuit.
  • 2
    Corroded or backed-out terminal in the B-circuit actuator connector.
  • 3
    Boost control B solenoid with an open internal winding.
  • 4
    Blown fuse or fusible link in the B-circuit power supply.
  • 5
    ECM/PCM internal driver failure on the boost control B output channel.
  • 6
    Wiring chafe or connector damage specific to the B-circuit routing path.
  • 7
    Connector seal failure allowing moisture ingress and terminal oxidation.

Symptoms drivers notice

MIL illuminated with possible limp-mode restriction.
Reduced or asymmetric boost pressure on twin-turbo applications.
Noticeable power loss particularly at higher engine speeds.
Scan tool boost pressure data shows deviation between commanded and actual boost.
Possible turbocharger noise changes or surging under load.

How to diagnose P2C2B

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs and freeze-frame data with a scan tool before any repairs.
  2. 2
    Visually inspect the B-circuit actuator wiring harness and connector for damage or corrosion.
  3. 3
    Measure the actuator coil resistance with the connector unplugged to check for an open winding.
  4. 4
    Check supply voltage at the actuator connector with the ignition on to verify power delivery.
  5. 5
    Test ground integrity at the actuator ground circuit.
  6. 6
    Perform a harness continuity test from the ECM connector pin to the actuator connector to locate the open.
  7. 7
    Replace damaged wiring, connectors, or actuator as indicated; retest and clear codes.

Vehicles where we've handled P2C2B

Platforms in our catalogue with confirmed P2C2B coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Is P2C2B specific to twin-turbo engines?

Not exclusively, but the B-circuit designation implies a second boost control channel, which is most common on twin-turbo, twin-scroll, or two-stage turbocharged engines.

Can P2C2B and P2C20 occur simultaneously?

Yes. If both boost control circuits are affected by a shared wiring fault such as a blown fuse or a common ground failure, both codes may set together.

How do I identify which actuator is circuit B?

Refer to the vehicle-specific wiring diagram, as the labelling varies by manufacturer. Circuit B is typically the secondary actuator in the system.

Does P2C2B affect fuel trims?

If the boost deviation is significant, the ECM may adjust fuelling through fuel trim corrections, which could be visible on a scan tool as positive or negative short-term fuel trim shifts.

Disabling P2C2B in software

RaceTune can permanently disable P2C2B — 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 P2C2B 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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