P24BF

SCR System Reagent Consumption Rationality

P24BF is a generic OBD-II powertrain diagnostic trouble code: SCR System Reagent Consumption Rationality. 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
P24BF
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24BF means

P24BF is set when the ECM determines that the rate of DEF (diesel exhaust fluid / AdBlue) consumption does not match the expected dosing quantity for the current operating conditions. The ECM compares actual DEF level change over time against the commanded dosing rate. A significant discrepancy in either direction triggers this rationality fault.

Over-consumption can indicate a DEF injector that is leaking or stuck open, while under-consumption or no consumption may indicate a blocked injector, a failed dosing pump, or a DEF level sensor fault reporting an incorrect level. The fault is designed to detect both excessive dosing that could damage the catalyst and insufficient dosing that could result in NOx emissions exceedance.

P24BF may appear alongside NOx efficiency or DEF system component codes. Diagnosis should focus on verifying the actual DEF level change matches the scan tool dosing data, and then tracing any discrepancy to the injector, pump, or level sensor. The fault will often clear once the underlying dosing system issue is resolved.

Common causes

Most-frequently reported root causes when P24BF is logged.

  • 1
    DEF injector stuck open or leaking, causing higher-than-commanded DEF consumption.
  • 2
    Blocked or failed DEF injector preventing reagent delivery while pump runs normally.
  • 3
    Faulty DEF level sensor providing an inaccurate tank level reading to the ECM.
  • 4
    Defective DEF dosing pump delivering incorrect flow rate despite receiving proper commands.
  • 5
    Crystallized DEF deposits partially blocking the delivery line, restricting flow.
  • 6
    Air leak in the DEF suction line causing inconsistent pump output and apparent consumption anomalies.
  • 7
    DEF return line blockage causing pressure irregularities that affect dosing accuracy.

Symptoms drivers notice

MIL illuminated; DEF system warning may also be present.
DEF tank level dropping faster or slower than expected between fill intervals.
Possible NOx efficiency fault codes appearing alongside P24BF.
DEF warning light indicating unexpected low level if over-consumption is occurring.
No immediate drivability change but emissions performance may be compromised.

How to diagnose P24BF

A typical diagnostic flow when this code is present.

  1. 1
    Read all DTCs and note any accompanying DEF injector, pump, NOx sensor, or efficiency fault codes.
  2. 2
    Check DEF tank level and compare to last known fill; calculate approximate consumption rate against mileage driven.
  3. 3
    Monitor commanded DEF dosing rate and actual DEF level on the scan tool during a drive cycle.
  4. 4
    Inspect the DEF injector for external leakage or crystallized deposits at the tip.
  5. 5
    Test DEF pump output pressure and flow rate against manufacturer specifications.
  6. 6
    Check DEF level sensor accuracy by comparing the scan tool reading to the actual measured tank level.
  7. 7
    Repair or replace faulty dosing components as identified and verify DEF consumption returns to normal after repair.

Vehicles where we've handled P24BF

Platforms in our catalogue with confirmed P24BF coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I top up the DEF tank to clear P24BF?

Topping up the DEF tank does not fix the underlying rationality fault. The code addresses a consumption rate discrepancy, not a low level condition. The root cause in the dosing system must be resolved.

What is normal DEF consumption relative to diesel fuel?

DEF consumption is typically in the range of 3 to 5 percent of diesel fuel consumption, but this varies by engine, load, and emissions standard. Check the vehicle specification for the expected ratio.

Can a frozen DEF system cause P24BF?

Yes. DEF freezes at approximately minus 11 degrees Celsius. If the DEF system heating is inadequate or faulty, frozen DEF can block delivery and cause a consumption rationality fault.

Is P24BF a serious fault?

It indicates the DEF dosing system is not operating as intended, which has emissions implications. While not immediately dangerous to the engine, it should be diagnosed promptly to avoid associated NOx efficiency faults and potential torque derates.

Disabling P24BF in software

RaceTune can permanently disable P24BF — 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 P24BF 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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