P2A70

SCR NOx Catalyst Efficiency Below Threshold Bank 1

P2A70 is a generic OBD-II powertrain diagnostic trouble code: SCR NOx Catalyst Efficiency Below Threshold Bank 1. 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
P2A70
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2A70 means

P2A70 is stored when the ECM determines that the Selective Catalytic Reduction (SCR) catalyst on bank 1 is not converting NOx emissions to acceptable levels. The ECM monitors NOx concentration upstream and downstream of the SCR catalyst using dedicated NOx sensors and compares the conversion efficiency against a calibrated threshold derived from the vehicle's emissions certification baseline.

The SCR system relies on precise dosing of diesel exhaust fluid (DEF/AdBlue) into the exhaust stream upstream of the catalyst. If dosing is insufficient, contaminated, or if the catalyst substrate itself has degraded, the downstream NOx concentration will remain elevated relative to the upstream reading, triggering this fault.

Continued operation with this code active may result in the vehicle entering a derate or inducement strategy under OBD regulations, progressively limiting engine power until the fault is corrected and the system is repaired and reset by a qualified technician.

Common causes

Most-frequently reported root causes when P2A70 is logged.

  • 1
    DEF/AdBlue quality is below specification (diluted or contaminated fluid).
  • 2
    DEF dosing injector is clogged, stuck closed, or delivering incorrect quantity.
  • 3
    SCR catalyst substrate has been thermally damaged or poisoned by fuel sulfur or oil ash.
  • 4
    Upstream or downstream NOx sensor has failed or drifted out of calibration.
  • 5
    DEF supply pump pressure is insufficient due to pump wear or a blocked strainer.
  • 6
    DEF tank level was allowed to run empty, causing catalyst deposit build-up.
  • 7
    Exhaust system leaks between the DEF injection point and the SCR catalyst are diluting reductant.

Symptoms drivers notice

MIL (check engine light) illuminated.
Possible progressive engine power reduction (inducement) if fault persists across multiple drive cycles.
DEF warning lamp may also be active if fluid quality is the root cause.
No immediately noticeable driveability change in early stages of the fault.

How to diagnose P2A70

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, record all stored DTCs, and note freeze-frame data for P2A70.
  2. 2
    Check DEF fluid quality using a refractometer to verify urea concentration (should be approximately 32.5%).
  3. 3
    Inspect DEF tank level and refill with certified fluid if low or contaminated.
  4. 4
    Read live NOx sensor values upstream and downstream at operating temperature to confirm sensor plausibility.
  5. 5
    Check for DEF dosing injector operation using functional test mode on the scan tool.
  6. 6
    Inspect exhaust system between DEF injection point and SCR catalyst for leaks or blockages.
  7. 7
    If sensor values and dosing appear correct, evaluate SCR catalyst efficiency via NOx conversion data and consider catalyst replacement.

Related powertrain codes

Frequently asked questions

Will the vehicle go into limp mode immediately when P2A70 is set?

Not immediately. Most manufacturers implement a stepped inducement strategy where power reduction occurs only after multiple failed drive cycles without repair.

Can topping off the DEF tank clear this code?

If poor DEF quality was the sole cause, refilling with certified fluid may allow the system to pass its efficiency monitor on the next drive cycle. However, the code must be cleared and a complete drive cycle run to confirm.

Is P2A70 the same as a failed NOx sensor code?

No. P2A70 specifically indicates catalyst conversion efficiency, not sensor circuit failure. NOx sensor faults have their own dedicated codes and should be resolved first before diagnosing efficiency codes.

How long does a drive cycle need to be to run the SCR efficiency monitor?

The SCR monitor typically requires sustained highway-speed driving at moderate to high load for several minutes to complete. Refer to the vehicle-specific OBD monitor readiness procedure for exact requirements.

Disabling P2A70 in software

RaceTune can permanently disable P2A70 — 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 P2A70 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 EDC16C31 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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