P22A1

NOx Sensor Circuit High (Bank 1 Sensor 2)

P22A1 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Circuit High (Bank 1 Sensor 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
P22A1
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P22A1 means

P22A1 is a generic SAE powertrain code that sets when the Engine Control Module (ECM) detects a signal voltage from the downstream NOx sensor (Bank 1, Sensor 2) that is above the expected maximum threshold. This sensor sits downstream of the Selective Catalytic Reduction (SCR) / AdBlue catalyst and measures residual nitrogen oxide concentration in the treated exhaust stream, providing closed-loop feedback to the SCR dosing system.

A high-circuit condition typically indicates a short to voltage in the sensor signal wire, an internally failed NOx sensor producing an out-of-range signal, or a fault in the ECM/DCM sensor supply circuit. Because the SCR system relies on this sensor for AdBlue dosing corrections, a confirmed fault will disable closed-loop SCR operation, potentially pushing NOx tailpipe emissions out of compliance.

P22A1 is the high-side companion to P22A0 (circuit low) and P22AA (circuit intermittent) for the same sensor position.

Common causes

Most-frequently reported root causes when P22A1 is logged.

  • 1
    Downstream NOx sensor (Bank 1 Sensor 2) internally failed — signal output shorted high or out-of-range
  • 2
    Short circuit to voltage (B+) on the NOx sensor signal wire or harness
  • 3
    Chafed, pinched, or heat-damaged wiring harness near the SCR/AdBlue catalyst
  • 4
    Corroded or contaminated sensor connector causing abnormal resistance
  • 5
    Faulty or damaged ECM/DCM NOx sensor input circuit
  • 6
    Incorrect or non-OEM replacement sensor with wrong signal range
  • 7
    AdBlue / DEF contamination of the exhaust stream causing sensor saturation

Symptoms drivers notice

Check Engine Light (MIL) illuminated
SCR/AdBlue system warning lamp or inducement message on dashboard
Increased NOx emissions (SCR closed-loop dosing disabled)
Possible engine torque de-rate after multiple drive cycles with active fault
No obvious driveability change in early stages; fuel economy may decline slightly

How to diagnose P22A1

A typical diagnostic flow when this code is present.

  1. 1
    Record freeze-frame data and all active/pending DTCs
  2. 2
    Perform a visual inspection of the downstream NOx sensor wiring harness and connector
  3. 3
    With a multimeter, measure signal voltage at the sensor connector
  4. 4
    Check sensor supply voltage and ground integrity at the connector
  5. 5
    Use a scan tool to monitor live NOx Sensor 2 PID data
  6. 6
    If wiring checks pass, substitute a known-good OEM NOx sensor and re-test
  7. 7
    If fault persists after sensor replacement, inspect ECM/DCM connector pins

Vehicles where we've handled P22A1

Platforms in our catalogue with confirmed P22A1 coverage.

BMW X5
2018–2019
BMW 530XD
2017
AUDI A4 20D
VW TRANSPORTER
AUDI A6
2015
BMW 320D
2016
AUDI A7 30D
AUDI A6 30D
2015

Related powertrain codes

Frequently asked questions

Can I drive with a P22A1 code active?

Short-term driving is usually possible, but the SCR/AdBlue system will operate in open-loop mode. On many Euro 6 and newer diesel vehicles, continued driving triggers a torque inducement after a set number of drive cycles.

Is P22A1 always caused by a bad NOx sensor?

Not necessarily. A high-circuit fault can equally be caused by a wiring short to voltage between the sensor and ECM.

What is the difference between P22A1 and P22A0?

P22A0 is the low-circuit companion code; P22A1 indicates the signal voltage is above the maximum threshold. Both affect the same downstream NOx sensor position (Bank 1, Sensor 2).

Does P22A1 affect AdBlue/DEF consumption?

Yes. The downstream NOx sensor is the primary feedback source for SCR dosing accuracy. When the ECM loses a valid signal, it will default to a fixed or reduced AdBlue injection strategy.

Disabling P22A1 in software

RaceTune can permanently disable P22A1 — 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 P22A1 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 EDC17C74 verified 2 software versions
  • Bosch EDC17C50 verified 1 software version
  • Bosch EDC17C56 verified 1 software version
  • Bosch EDC17CP44 verified 1 software version
  • Bosch MD1CP002 verified 1 software version
  • Bosch MD1CP004 verified 1 software version
  • Bosch MD1CS001 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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