P2C4C

Exhaust Gas Recirculation Sensor B Circuit Low

P2C4C is a generic OBD-II powertrain diagnostic trouble code: Exhaust Gas Recirculation Sensor B 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
P2C4C
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2C4C means

P2C4C indicates the ECM has detected a signal voltage from EGR sensor circuit B that is below the minimum acceptable threshold. On vehicles equipped with dual EGR sensors or a high-pressure/low-pressure EGR split, circuit B monitors the secondary sensor in the arrangement, which may measure differential pressure, temperature, or valve position on the second stage of the EGR system.

With the B circuit reading below the threshold, the ECM cannot close the loop on the secondary EGR path, forcing open-loop or reduced EGR operation. This affects combustion temperatures and emissions control, particularly NOx output. Depending on calibration, a limp mode restriction may also be applied.

Diagnosis should begin with a visual inspection of the wiring harness and connectors for the B-bank EGR sensor. Sensor supply voltage, signal integrity, and ground path quality should all be verified before replacing the sensor itself.

Common causes

Most-frequently reported root causes when P2C4C is logged.

  • 1
    Short to ground on the EGR sensor B signal wire.
  • 2
    Failed EGR sensor B producing a below-minimum voltage.
  • 3
    Loss of 5V reference supply to sensor B.
  • 4
    Corroded or loose connector at the EGR sensor B location.
  • 5
    Wiring harness chafing or heat damage near the EGR cooler.
  • 6
    Internal ECM fault on the B sensor input channel.
  • 7
    Moisture ingress in the sensor or connector body.

Symptoms drivers notice

MIL illuminated.
EGR B circuit disabled or operating open-loop.
Elevated exhaust emissions, particularly NOx.
Possible reduced fuel economy.
May trigger additional emission system faults on repeated drive cycles.

How to diagnose P2C4C

A typical diagnostic flow when this code is present.

  1. 1
    Scan for all active and pending DTCs to identify companion codes.
  2. 2
    Review freeze frame data to note conditions when P2C4C was set.
  3. 3
    Locate the EGR sensor B per the vehicle wiring diagram and inspect its connector.
  4. 4
    Measure 5V reference and ground at the sensor connector with ignition on.
  5. 5
    Test the signal wire for continuity and short to ground between sensor and ECM.
  6. 6
    Compare live sensor B voltage against sensor A to identify discrepancy.
  7. 7
    Replace sensor B if supply and wiring checks are satisfactory and fault persists.

Vehicles where we've handled P2C4C

Platforms in our catalogue with confirmed P2C4C coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

What is the difference between P2C48 and P2C4C?

P2C48 refers to EGR sensor circuit A (primary) while P2C4C refers to circuit B (secondary); both indicate a low voltage electrical fault but on different sensor circuits.

Can both A and B codes appear together?

Yes, if a shared 5V reference supply is faulty, both circuits can fall below threshold simultaneously.

Is this code common on high-mileage diesels?

Yes, EGR system sensors are exposed to soot and heat, and connector corrosion becomes more common with age and high mileage.

Does this code require an EGR cooler inspection?

Not necessarily for the electrical fault itself, but EGR cooler leaks can contaminate sensor connectors, so it is worth inspecting in high-mileage vehicles.

Disabling P2C4C in software

RaceTune can permanently disable P2C4C — 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 P2C4C 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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