P2C4D

Exhaust Gas Recirculation Sensor B Circuit High

P2C4D is a generic OBD-II powertrain diagnostic trouble code: Exhaust Gas Recirculation Sensor 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
P2C4D
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2C4D means

P2C4D is stored when the ECM detects that the EGR sensor B circuit voltage is above the maximum acceptable threshold. Unlike the companion low code P2C4C, a high circuit condition points to a different class of electrical faults including open circuits, short to voltage, or a sensor that has failed with its output stuck near the supply rail.

When the EGR sensor B signal is abnormally high, the ECM cannot determine accurate EGR flow or valve position for the B circuit, and EGR control is degraded or disabled. This raises combustion temperatures and NOx emissions, and can affect turbocharger behavior in systems where EGR and boost control interact.

Begin diagnosis by checking for an open circuit in the signal return path, a short of the signal wire to a 5V or 12V source, or a failed sensor. Inspect connectors for spread or backed-out pins that could cause a floating or shorted signal.

Common causes

Most-frequently reported root causes when P2C4D is logged.

  • 1
    Open circuit in the EGR sensor B signal wire.
  • 2
    Sensor B signal wire shorted to a voltage source (5V or 12V).
  • 3
    Failed EGR sensor B with output stuck high.
  • 4
    Backed-out or spread pin in the sensor B connector.
  • 5
    Damaged wiring with chafed insulation contacting a power wire.
  • 6
    Faulty ECM input circuit for sensor B channel.
  • 7
    Sensor ground circuit open, causing apparent high signal.

Symptoms drivers notice

MIL illuminated.
EGR B circuit disabled or operating in default mode.
Elevated NOx emissions.
Possible slight drivability concern under EGR-dependent load conditions.
May set companion EGR operational codes on extended fault duration.

How to diagnose P2C4D

A typical diagnostic flow when this code is present.

  1. 1
    Connect scan tool and record all DTCs including companion EGR codes.
  2. 2
    Check live EGR sensor B voltage; high circuit expects reading above maximum threshold.
  3. 3
    Inspect sensor B connector for backed-out pins, corrosion, or damage.
  4. 4
    Check sensor B ground circuit continuity back to ECM ground.
  5. 5
    Test signal wire for short to 5V reference or battery voltage.
  6. 6
    Perform a sensor B resistance or output test per manufacturer specification.
  7. 7
    Replace sensor B if wiring and connector are confirmed good.

Vehicles where we've handled P2C4D

Platforms in our catalogue with confirmed P2C4D coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Why would a sensor output be stuck high?

A sensor with an internal open circuit or a broken element often allows the input to float to the ECM pull-up voltage, which appears as a high reading.

Can P2C4D and P2C4C set at the same time?

Not typically from the same fault; they indicate opposite electrical conditions, though intermittent faults can cause either to appear in stored history.

Does this code always mean the sensor is bad?

No. An open signal wire between sensor and ECM is a common cause and should be ruled out before replacing the sensor.

How do I check for a short to voltage on the signal wire?

Disconnect the sensor and measure voltage at the harness-side signal pin with ignition on; any voltage reading indicates a short to a power source.

Disabling P2C4D in software

RaceTune can permanently disable P2C4D — 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 P2C4D 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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