P290B

Reductant Injection System Incorrect Flow

P290B is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection System Incorrect Flow. 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
P290B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P290B means

P290B is set when the engine control module (ECM) or selective catalytic reduction (SCR) control module detects that the actual reductant (DEF/AdBlue) flow rate does not match the commanded flow rate during normal SCR operation. The module monitors injector feedback, pressure sensor data, and downstream NOx sensor readings to infer whether the correct quantity of reductant is being delivered to the exhaust stream.

Common root causes include a partially clogged reductant injector, a weak or failing reductant pump that cannot maintain sufficient delivery pressure, or air intrusion into the reductant supply line. Low reductant fluid level or degraded fluid quality can also reduce effective delivery. In cold climates, frozen reductant in lines or the tank can temporarily trigger this fault until the system thaws and re-primes.

Because NOx reduction efficiency depends on precise reductant dosing, prolonged operation with this fault active can result in elevated tailpipe NOx emissions and, on some vehicles, an active derate or inducement strategy. Technicians should verify actual flow against commanded flow using live data before condemning any component.

Common causes

Most-frequently reported root causes when P290B is logged.

  • 1
    Clogged or fouled reductant (DEF) injector restricting flow.
  • 2
    Weak or failing reductant supply pump unable to meet commanded pressure.
  • 3
    Air intrusion or leak in the reductant supply line causing inconsistent delivery.
  • 4
    Frozen reductant in tank, lines, or injector in sub-zero conditions.
  • 5
    Degraded or contaminated DEF fluid with incorrect urea concentration.
  • 6
    Faulty reductant flow sensor or pressure sensor providing incorrect feedback.
  • 7
    Blocked reductant strainer or filter reducing system flow capacity.

Symptoms drivers notice

Malfunction indicator lamp (MIL) illuminated.
Increased tailpipe NOx emissions, possible emissions test failure.
SCR system efficiency monitor flagged in freeze frame data.
Possible engine derate or torque reduction on vehicles with inducement strategy.
DEF consumption may appear lower than expected.

How to diagnose P290B

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all active and pending DTCs along with freeze frame data.
  2. 2
    Check reductant fluid level and verify DEF quality with a refractometer.
  3. 3
    Inspect the reductant supply lines and fittings for leaks, kinks, or air intrusion points.
  4. 4
    Monitor reductant pump pressure and commanded vs. actual flow rate in live data.
  5. 5
    Perform a reductant injector flow test using the scan tool bi-directional controls if available.
  6. 6
    Inspect and clean or replace the reductant strainer and injector if flow is confirmed low.
  7. 7
    Clear codes, perform a drive cycle, and confirm the fault does not return before returning the vehicle.

Vehicles where we've handled P290B

Platforms in our catalogue with confirmed P290B coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I drive with P290B active?

Short-term driving is generally possible, but continued operation with incorrect reductant flow elevates NOx emissions and may trigger an engine derate or inducement countdown on some vehicles.

Will bad DEF fluid cause P290B?

Yes. Diluted, contaminated, or incorrect concentration DEF can cause the SCR system to detect a mismatch between commanded and actual NOx reduction, setting this code.

Does P290B always mean the injector needs replacement?

Not necessarily. A clogged injector can sometimes be cleaned. Diagnose the pump, lines, and fluid quality first before replacing the injector.

Is P290B related to P20EE or P203F?

They share the SCR/reductant system but target different sub-components. P20EE targets SCR efficiency, P203F targets reductant quality, and P290B specifically targets incorrect flow rate.

Disabling P290B in software

RaceTune can permanently disable P290B — 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 P290B 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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