P2527

Reductant Injection Air Supply Control Circuit High

P2527 is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Air Supply Control Circuit High. 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
P2527
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2527 means

P2527 is set when the ECM/PCM detects a high voltage condition in the air supply control circuit for the reductant (DEF/AdBlue) injection system. This circuit controls the air compressor or pump that pressurises the reductant delivery line in air-assisted SCR dosing systems.

The high voltage signal typically indicates a short to voltage in the wiring harness, a failed driver circuit within the reductant control module, or an open-circuit condition that causes the control signal to float high. The fault causes the ECM to disable reductant dosing to prevent hardware damage.

Continued operation without a functioning SCR system will lead to elevated NOx tailpipe emissions and, on vehicles with NOx-reduction enforcement strategies, can trigger a progressive engine derate or no-start condition after a defined number of drive cycles.

Common causes

Most-frequently reported root causes when P2527 is logged.

  • 1
    Short to voltage in the reductant air supply control wiring harness.
  • 2
    Failed or damaged reductant dosing control module with defective output driver.
  • 3
    Chafed or pinched wiring between the ECM and the air supply actuator.
  • 4
    Corroded or loose connector at the reductant air pump or control module.
  • 5
    Open circuit in the return (ground) path of the air supply control circuit.
  • 6
    Internal failure of the reductant air supply pump causing excessive back-EMF.

Symptoms drivers notice

MIL (check engine light) illuminated.
SCR system inactive or reduced reductant dosing.
Increased NOx emissions detected by downstream NOx sensor.
Possible engine derate or torque limitation after multiple drive cycles.
Reductant system warning indicator on the instrument cluster.

How to diagnose P2527

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored DTCs and freeze frame data before clearing.
  2. 2
    Check live data for the reductant air supply control circuit voltage and duty cycle.
  3. 3
    Inspect the wiring harness between the ECM and reductant air pump for shorts, chafing, or corrosion.
  4. 4
    Measure voltage at the air supply control circuit connector with ignition on; voltage significantly above commanded level indicates a short to voltage.
  5. 5
    Inspect and clean connector terminals at the reductant dosing module and air pump.
  6. 6
    Test the resistance of the air supply actuator coil against manufacturer specification.
  7. 7
    Replace or repair wiring/connector before condemning the control module or pump.

Vehicles where we've handled P2527

Platforms in our catalogue with confirmed P2527 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I drive with P2527 active?

Short-term driving is possible but the SCR system will not function correctly, leading to high NOx emissions and potential derate after several drive cycles.

Does P2527 always mean the air pump has failed?

Not necessarily. A wiring short or connector fault is equally likely; always inspect the circuit before replacing hardware.

Will clearing the code fix the problem?

No. The code will return on the next drive cycle unless the underlying wiring or component fault is corrected.

Is P2527 a smog-test failure?

Yes. Any active MIL-on emissions-related DTC will typically result in a failed emissions inspection.

Disabling P2527 in software

RaceTune can permanently disable P2527 — 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 P2527 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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