P24C6

Reductant Injection Quantity Too Low

P24C6 is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Quantity Too 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
P24C6
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P24C6 means

P24C6 is stored when the ECM determines that the quantity of DEF being injected into the exhaust is lower than the demanded amount. The SCR system's dosing control module continuously calculates the required DEF injection rate based on engine-out NOx, exhaust flow, temperature, and SCR catalyst state. A shortfall in actual versus demanded dosing triggers this fault.

Common causes include a partially blocked dosing nozzle due to urea crystallization, low DEF supply pressure, a worn or failing dosing module, or air ingestion into the DEF supply line causing inconsistent metering. The fault can also be triggered by a DEF quality issue where concentration is below specification, effectively reducing the reductant content per unit volume dosed.

When dosing quantity is insufficient, the downstream NOx sensor will detect reduced conversion efficiency and the ECM may log additional NOx performance codes alongside P24C6. Extended operation in this condition will lead to NOx emission violations and may trigger progressive torque derate. Diagnosis should include DEF pressure verification, dosing module actuation tests, and injector flow checks before replacement.

Common causes

Most-frequently reported root causes when P24C6 is logged.

  • 1
    Dosing nozzle partially blocked by urea crystallization.
  • 2
    Low DEF supply pressure reducing flow through the dosing module.
  • 3
    Air ingestion into the DEF supply line causing inconsistent metering.
  • 4
    Worn or degraded DEF dosing module with reduced flow capacity.
  • 5
    Incorrect DEF concentration (too dilute) reducing effective reductant per dose.
  • 6
    DEF filter partially clogged restricting supply flow.
  • 7
    Dosing module control circuit fault affecting pulse width accuracy.

Symptoms drivers notice

MIL illuminated.
Reduced SCR NOx conversion efficiency detectable via scan tool.
Possible torque derate after extended fault duration.
DEF system warning on instrument cluster.
No perceptible drivability change in early stages.

How to diagnose P24C6

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and check all stored DTCs including NOx, pressure, and dosing faults.
  2. 2
    Review live data for DEF pressure and demanded versus actual dosing quantity.
  3. 3
    Check DEF quality with a refractometer for correct urea concentration.
  4. 4
    Inspect the DEF supply line for air ingestion points or leaks.
  5. 5
    Perform a dosing module actuation test via the scan tool and observe pressure drop and flow.
  6. 6
    Inspect and clean or replace the DEF filter if restricted.
  7. 7
    Remove and inspect the dosing nozzle for crystallization blockage; clean or replace as needed.

Vehicles where we've handled P24C6

Platforms in our catalogue with confirmed P24C6 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can diluted DEF cause P24C6?

Yes. DEF that is too dilute contains less urea per volume than required. The system doses by volume, so the actual reductant delivered falls short of the demand, triggering the low-quantity fault.

How do I test if the dosing nozzle is blocked?

A scan tool actuation test that commands dosing while monitoring pressure drop can reveal a blocked nozzle. Physical removal and visual inspection for white crystalline deposits is the definitive check.

Will flushing the DEF system fix P24C6?

If crystallization is the cause, flushing with clean distilled water can help clear blockages. However, worn components or low pressure require repair or replacement.

Is P24C6 always a dosing module fault?

No. Supply pressure, DEF quality, and line restrictions should be ruled out first as they are more common and less expensive to address than a failed dosing module.

Disabling P24C6 in software

RaceTune can permanently disable P24C6 — 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 P24C6 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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