P24C8

NOx Sensor Circuit Range/Performance Bank 1 Sensor 2 (Downstream of SCR)

P24C8 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Circuit Range/Performance Bank 1 Sensor 2 (Downstream of SCR). 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
P24C8
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24C8 means

P24C8 is set when the PCM/ECM detects that the signal from the downstream NOx sensor (Bank 1, Sensor 2, located after the Selective Catalytic Reduction catalyst) is outside the expected range or does not respond as predicted during SCR system operation. The sensor output may be implausibly high, implausibly low, or may not track changes in exhaust NOx concentration correctly.

This code is specific to the downstream NOx sensor used to verify SCR conversion efficiency. The control module compares measured tailpipe NOx levels against a model of expected post-SCR concentration; a significant or sustained deviation triggers the fault. Common causes include a degraded sensor element, contamination from urea deposit buildup, or wiring faults between the sensor and ECM.

With this code active, the system may default to a fixed DEF dosing strategy and SCR efficiency monitoring is impaired. Emissions compliance cannot be confirmed, so MIL illumination is required. The fault does not typically induce limp mode on its own but may combine with other SCR codes to do so.

Common causes

Most-frequently reported root causes when P24C8 is logged.

  • 1
    Failed or contaminated downstream NOx sensor element.
  • 2
    Urea (DEF) deposit buildup on the sensor tip causing signal contamination.
  • 3
    Open circuit, short to voltage, or short to ground in the NOx sensor signal wire.
  • 4
    Corroded or damaged sensor connector.
  • 5
    Exhaust system leak upstream of the sensor altering NOx concentration readings.
  • 6
    SCR catalyst severely degraded, producing an implausible post-catalyst NOx signal.
  • 7
    Faulty ECM/PCM NOx sensor input circuit (rare).

Symptoms drivers notice

Malfunction Indicator Lamp (MIL) illuminated.
Possible increase in tailpipe NOx emissions.
SCR system efficiency monitoring disabled or inaccurate.
DEF consumption may be abnormal due to open-loop dosing fallback.
No perceptible drivability change in most cases.

How to diagnose P24C8

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored DTCs and freeze-frame data before clearing anything.
  2. 2
    Inspect the downstream NOx sensor connector and wiring harness for corrosion, chafing, or loose pins.
  3. 3
    Check for exhaust leaks between the SCR outlet and the sensor bung that could dilute or contaminate the sample.
  4. 4
    Review live NOx sensor data at idle and under load; compare upstream vs. downstream readings for plausibility.
  5. 5
    Inspect the sensor tip for urea crystal deposits or soot fouling; clean if manufacturer procedure permits.
  6. 6
    Perform a sensor heater circuit resistance check per the manufacturer service manual.
  7. 7
    Replace the downstream NOx sensor if wiring and exhaust integrity are confirmed good and the signal remains out of range.

Vehicles where we've handled P24C8

Platforms in our catalogue with confirmed P24C8 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I drive with P24C8 active?

Short-term driving is generally possible as limp mode is not typically triggered by this code alone, but NOx emissions will be unmonitored and the MIL will remain on. Rectify as soon as practical.

Will clearing the code make it go away permanently?

No. The code will return on the next drive cycle if the root cause (sensor fault, wiring issue, or exhaust leak) is not repaired.

Is the downstream NOx sensor the same part as the upstream one?

Not necessarily. Upstream and downstream sensors may differ in calibration range and connector type; always verify the correct part number for the specific sensor position before replacing.

Could a bad SCR catalyst set P24C8?

Yes. A severely deteriorated SCR catalyst that passes NOx unchanged can cause the downstream sensor to read values outside the expected post-conversion window, triggering a range/performance fault.

Disabling P24C8 in software

RaceTune can permanently disable P24C8 — 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 P24C8 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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