P27CB

Turbocharger Boost Control Position Sensor A Circuit Low

P27CB is a generic OBD-II powertrain diagnostic trouble code: Turbocharger Boost Control Position Sensor A Circuit Low. 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
P27CB
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
Need P27CB disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
→

What P27CB means

P27CB is stored when the PCM detects a voltage on the turbocharger boost control position sensor A signal circuit that is below the calibrated minimum operating range. Position sensor A monitors the physical travel of the turbocharger actuator, VGT vane rack, or wastegate linkage, providing closed-loop feedback to the PCM for precise boost control.

A circuit-low reading on this sensor typically results from a short to ground on the signal wire, an open 5-volt reference circuit to the sensor, a damaged or failed sensor producing a near-zero output, or a poor sensor ground. The PCM cannot rely on an out-of-range signal for boost control and will substitute a default strategy, usually reducing power to protect the engine.

Because the 5-volt reference is often shared with other sensors, a pulled-low reference line can set multiple codes simultaneously. Technicians should always check for companion codes before beginning component replacement, as a single wiring fault can trigger several related DTCs across different sensor circuits sharing the same reference.

Common causes

Most-frequently reported root causes when P27CB is logged.

  • 1
    Short to ground on the position sensor A signal wire.
  • 2
    Open or shorted 5-volt reference circuit supplying sensor A.
  • 3
    Failed position sensor A with internal short producing a low output signal.
  • 4
    Poor or missing sensor ground connection.
  • 5
    Damaged wiring in the sensor harness where insulation has worn through.
  • 6
    Moisture or corrosion in the sensor connector causing signal leakage to ground.
  • 7
    Failed PCM internal reference supply affecting the sensor input circuit.

Symptoms drivers notice

MIL on with possible limp-home power reduction.
Boost pressure not building normally or being held at a fixed low level.
Scan tool shows position sensor A voltage at or near 0 V in live data.
Hesitation or flat spot during acceleration under boost demand.
Possible companion codes from other sensors sharing the same 5-volt reference.

How to diagnose P27CB

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note any companion sensor codes that may indicate a shared reference fault.
  2. 2
    With the ignition on, measure the 5-volt reference voltage at the position sensor A connector.
  3. 3
    Check the signal wire voltage at the connector; a reading near 0 V with ignition on suggests a short to ground.
  4. 4
    Inspect the wiring harness and connector for corrosion, damaged insulation, or pinched wires.
  5. 5
    Measure sensor ground circuit continuity back to the PCM.
  6. 6
    Substitute a known-good sensor to confirm whether the fault is internal to the sensor or in the wiring.
  7. 7
    If all external circuits check out, evaluate the PCM reference supply output for the sensor circuit.

Vehicles where we've handled P27CB

Platforms in our catalogue with confirmed P27CB coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Why does P27CB sometimes appear with other sensor codes?

Many sensors share a common 5-volt reference from the PCM. If that reference wire shorts to ground, all sensors on that circuit will read low and set corresponding codes simultaneously.

Is 0 V on the signal wire always a short to ground?

Usually, but an open sensor ground can also collapse the signal toward 0 V. Check both the signal wire and the ground circuit before assuming a short.

Can I drive with P27CB active?

Driving with active boost control faults is not recommended. The PCM may restrict power significantly, and continued operation without proper boost management can damage the turbocharger.

How do I differentiate a bad sensor from a wiring fault?

Disconnect the sensor and measure the 5-volt reference and ground at the harness side connector. If reference and ground are correct but the signal is still low, the sensor itself is faulty.

Disabling P27CB in software

RaceTune can permanently disable P27CB — 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 P27CB 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.

Got P27CB in your scan?

Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.

Upload your file