P24CF

SCR NOx Catalyst Efficiency Below Threshold Bank 2

P24CF is a generic OBD-II powertrain diagnostic trouble code: SCR NOx Catalyst Efficiency Below Threshold Bank 2. 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
P24CF
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P24CF means

P24CF mirrors P24AF but applies to the Bank 2 SCR catalyst on engines with dual-bank exhaust aftertreatment systems. It is set when the NOx conversion efficiency of the Bank 2 SCR catalyst falls below the calibrated minimum threshold as measured by the surrounding NOx sensors and DEF dosing data.

Dual-bank SCR systems are common on V-configuration diesel engines and larger inline engines where separate exhaust tracts each require independent dosing and monitoring. Each bank has its own DEF injector, NOx sensors, and in some architectures its own dosing pump or metering valve, so a Bank 2 fault may coexist with a functioning Bank 1 system.

The diagnostic approach is identical to P24AF but focused on Bank 2 components: verify the Bank 2 DEF injector is dosing correctly, check Bank 2 NOx sensor accuracy, inspect for DEF line restrictions specific to Bank 2, and evaluate the DEF fluid quality. As with Bank 1, exhaust a full electrical and fluidic check of the dosing system before recommending catalyst replacement.

Common causes

Most-frequently reported root causes when P24CF is logged.

  • 1
    Bank 2 DEF injector fault reducing or stopping reductant delivery.
  • 2
    Clogged Bank 2 DEF supply line or injector tip.
  • 3
    Contaminated or diluted DEF affecting both banks.
  • 4
    Degraded, poisoned, or thermally damaged Bank 2 SCR catalyst.
  • 5
    Faulty Bank 2 downstream NOx sensor producing falsely high readings.
  • 6
    Faulty Bank 2 upstream NOx sensor distorting the efficiency calculation.
  • 7
    Bank 2 DEF metering valve or pump fault on systems with per-bank hardware.
  • 8
    Exhaust cross-talk or leak between banks affecting NOx measurements.

Symptoms drivers notice

MIL or SCR/NOx warning lamp illuminated.
Elevated tailpipe NOx emissions.
Possible engine power derate on systems enforcing NOx compliance.
Potential asymmetric DEF consumption between banks.

How to diagnose P24CF

A typical diagnostic flow when this code is present.

  1. 1
    Read all DTCs with a scan tool; determine whether Bank 1 codes are also present or only Bank 2.
  2. 2
    Verify DEF quality with a refractometer for correct urea concentration.
  3. 3
    Check Bank 2 DEF dosing live data including commanded injection quantity and delivery confirmation.
  4. 4
    Inspect the Bank 2 DEF injector and supply line for blockage or electrical faults.
  5. 5
    Compare Bank 2 upstream and downstream NOx sensor readings for plausibility.
  6. 6
    Perform a sensor substitution or plausibility test on Bank 2 NOx sensors before condemning the catalyst.
  7. 7
    If all dosing and sensor checks pass, assess Bank 2 SCR catalyst condition and consider replacement.

Vehicles where we've handled P24CF

Platforms in our catalogue with confirmed P24CF coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

If only P24CF is set and not P24AF, does that mean Bank 1 is fine?

It suggests Bank 1 efficiency is currently above threshold, but both banks share the same DEF fluid, so contamination issues would eventually affect both; investigate DEF quality in either case.

Are Bank 1 and Bank 2 SCR catalysts usually the same part?

On many V-engine platforms the Bank 1 and Bank 2 SCR catalysts are identical parts, making it straightforward to swap for diagnostic confirmation if warranted.

Can I drive with P24CF?

The vehicle will typically continue to run, but NOx emissions are elevated and an active MIL will fail emissions testing; a power derate may activate if the fault is persistent.

What is the most common fix for P24CF?

In practice, faulty Bank 2 DEF injectors and NOx sensors are more common fixes than catalyst replacement; always complete electrical and dosing system checks first.

Disabling P24CF in software

RaceTune can permanently disable P24CF — 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 P24CF 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
  • Bosch EDC17CP09 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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