P24B1

SCR NOx Catalyst Efficiency Below Threshold Bank 2

P24B1 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
P24B1
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24B1 means

P24B1 mirrors P24B0 but applies to bank 2 on engines with two cylinder banks and separate exhaust paths, each equipped with its own SCR catalyst. The ECM monitors NOx conversion efficiency independently on each bank and sets P24B1 when bank 2 SCR efficiency falls below the required threshold.

The diagnostic approach is identical to P24B0: the ECM compares upstream and downstream NOx sensor values on bank 2 to calculate real-time conversion efficiency. The fault can originate from a degraded catalyst, a faulty NOx sensor on the bank 2 exhaust path, insufficient DEF dosing to that catalyst, or contaminated DEF.

On V-configuration engines where each bank has a dedicated SCR, it is important to determine whether both P24B0 and P24B1 are present simultaneously, which could point to a shared root cause such as DEF quality or a common dosing pump, versus a single-bank fault which is more likely to indicate a bank-specific catalyst or sensor issue.

Common causes

Most-frequently reported root causes when P24B1 is logged.

  • 1
    SCR catalyst on bank 2 degraded or poisoned, reducing NOx conversion below the required threshold.
  • 2
    Faulty downstream NOx sensor on the bank 2 exhaust path providing a biased efficiency reading.
  • 3
    Insufficient or absent DEF dosing to the bank 2 SCR due to a blocked injector or dosing circuit fault.
  • 4
    Contaminated or improperly concentrated DEF reducing the chemical reduction reaction on bank 2.
  • 5
    Exhaust leak between the DEF injection point and the bank 2 SCR catalyst.
  • 6
    Faulty upstream NOx sensor on bank 2 causing incorrect DEF dosing to that bank.
  • 7
    Mixer or swirl element blockage on the bank 2 exhaust path reducing DEF distribution uniformity.

Symptoms drivers notice

MIL illuminated; DEF or emissions warning may also be present.
No immediate drivability impact in early fault stages.
Potential torque or speed derate after an extended fault period per regulatory requirements.
Possible asymmetric DEF consumption if only bank 2 dosing is affected.
Elevated NOx emissions from the bank 2 exhaust path.

How to diagnose P24B1

A typical diagnostic flow when this code is present.

  1. 1
    Read all DTCs and note whether P24B0 is also present, which may indicate a shared DEF system fault.
  2. 2
    Check DEF fluid quality and urea concentration; replace with certified DEF if contamination is suspected.
  3. 3
    Monitor bank 2 upstream and downstream NOx sensor readings and DEF dosing rate in live data.
  4. 4
    Inspect the bank 2 DEF injector and associated dosing lines for blockage or damage.
  5. 5
    Verify NOx sensor operation on bank 2 by reviewing sensor response to engine load changes.
  6. 6
    Check for exhaust leaks on the bank 2 side between the DEF injection port and the SCR outlet.
  7. 7
    Assess bank 2 SCR catalyst condition through live efficiency data before recommending replacement.

Related powertrain codes

Frequently asked questions

If both P24B0 and P24B1 are set together, what does that suggest?

Both codes appearing simultaneously often points to a shared system fault such as DEF quality, a common dosing pump failure, or a calibration issue rather than two independent catalyst failures.

Can I drive with P24B1 active?

Short-term driving is possible, but the fault will typically trigger a vehicle derate if not resolved within the regulatory window. Address it promptly to avoid power restrictions.

Do all vehicles have a bank 2 SCR?

No. P24B1 only applies to engines with two exhaust banks each equipped with a separate SCR catalyst, such as larger V6, V8, or V10 diesel engines.

Is bank 2 always the passenger side?

Bank designation varies by manufacturer. Consult the vehicle-specific service manual to confirm which physical bank corresponds to bank 2 for wiring and component access.

Disabling P24B1 in software

RaceTune can permanently disable P24B1 — 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 P24B1 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 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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