P2A85

NOx Sensor Heater Circuit Low Bank 2 Sensor 1

P2A85 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Heater Circuit Low Bank 2 Sensor 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
P2A85
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2A85 means

P2A85 is set when the ECM detects that the current draw or voltage on the NOx sensor heater circuit for bank 2 sensor 1 is below the expected level. The heater element inside a NOx sensor must bring the sensor to its operating temperature rapidly and maintain it within a tight window, as NOx measurement accuracy is highly temperature-dependent. A low-circuit condition suggests the heater is drawing less current than expected, pointing to an open heater element, a broken supply wire, or a failed relay or fuse in the heater supply path.

Unlike heated oxygen sensors, the NOx sensor heater circuit is typically higher-power and may be controlled by a dedicated power stage in the ECM or through a separate solid-state relay. Failure of this control stage can produce the same low-circuit symptom even when the heater element itself is intact.

With the heater inoperative, the sensor will not reach its design operating temperature and will produce unreliable NOx readings, preventing closed-loop DEF dosing control and causing associated efficiency and performance codes to accumulate over time.

Common causes

Most-frequently reported root causes when P2A85 is logged.

  • 1
    Open heater element inside the NOx sensor assembly.
  • 2
    Broken or corroded heater supply wire between the fuse/relay and the sensor connector.
  • 3
    Blown fuse in the NOx sensor heater supply circuit.
  • 4
    Failed ECM internal power stage for the heater circuit.
  • 5
    High-resistance connector joint causing a voltage drop that prevents sufficient heater current.
  • 6
    Damaged wiring insulation resulting in an intermittent open in the heater circuit.

Symptoms drivers notice

MIL illuminated.
NOx sensor may report implausible readings until it self-heats via exhaust gas at high load.
Slow SCR catalyst warm-up and potentially elevated NOx emissions during cold start.
Possible companion sensor performance or efficiency codes after extended driving with a cold sensor.

How to diagnose P2A85

A typical diagnostic flow when this code is present.

  1. 1
    Read all DTCs; confirm P2A85 is present and note any related performance or efficiency codes.
  2. 2
    Locate the NOx sensor heater fuse in the fuse box and inspect it; replace if blown and retest.
  3. 3
    Inspect the heater supply wiring from the fuse to the sensor connector for open circuits or corrosion.
  4. 4
    Measure heater element resistance across the heater pins on the sensor connector; an open reading confirms a failed element.
  5. 5
    If resistance is within specification, check heater supply voltage at the sensor connector with ignition on.
  6. 6
    Test the ECM heater control output if supply voltage is confirmed good but heater does not activate.
  7. 7
    Replace the sensor if the element is open; repair wiring or replace the fuse as appropriate for other findings.

Vehicles where we've handled P2A85

Platforms in our catalogue with confirmed P2A85 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Will the NOx sensor still work at all without the heater?

At high exhaust temperatures during sustained load, the sensor may reach operating temperature passively, but cold-start and low-load accuracy will be significantly compromised.

Is P2A85 a sensor replacement job or a wiring job?

Both are possible. Check the fuse and wiring continuity first. If those are intact and the heater element measures open, the sensor requires replacement.

Can I drive the vehicle with P2A85?

The vehicle will typically remain driveable, but NOx conversion accuracy will be reduced and further efficiency faults may accumulate, potentially leading to an inducement derate.

How do I measure NOx sensor heater resistance?

Disconnect the sensor connector and measure resistance between the two heater supply pins (not the signal pins). The exact expected value depends on the sensor model; consult the vehicle service data for the specification.

Disabling P2A85 in software

RaceTune can permanently disable P2A85 — 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 P2A85 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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