P24B3

NOx Sensor Circuit High Voltage Bank 1 Sensor 1

P24B3 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Circuit High Voltage Bank 1 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
P24B3
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24B3 means

P24B3 is stored when the powertrain control module (PCM) detects a signal voltage from the upstream NOx sensor (Bank 1, Sensor 1) that is higher than the expected operating range for a sustained period. The upstream NOx sensor is located ahead of the selective catalytic reduction (SCR) catalyst and measures raw exhaust NOx concentration leaving the engine.

The sensor generates an output signal that the PCM uses to calculate reductant dosing strategy. When the signal remains above the defined threshold, the module cannot accurately determine engine-out NOx levels, which compromises emissions control. The fault may be caused by a wiring short to voltage, a failed sensor, or a fault internal to the sensor control module.

Because accurate NOx measurement is essential for meeting emissions regulations, most vehicle manufacturers will illuminate the malfunction indicator lamp (MIL) and may limit SCR dosing or flag a SCR system malfunction if the condition persists across multiple drive cycles.

Common causes

Most-frequently reported root causes when P24B3 is logged.

  • 1
    Short circuit to battery voltage in the NOx sensor signal wire.
  • 2
    Failed or internally shorted upstream NOx sensor (Bank 1 Sensor 1).
  • 3
    Faulty NOx sensor control module or interface circuit.
  • 4
    Damaged wiring harness chafing against engine components causing intermittent short.
  • 5
    Corroded or contaminated sensor connector causing elevated resistance or leakage current.
  • 6
    PCM software fault misinterpreting sensor signal voltage.
  • 7
    Incorrect replacement sensor installed with incompatible output range.

Symptoms drivers notice

MIL (check engine light) illuminated.
SCR system operating in reduced or open-loop dosing mode.
Possible increase in tailpipe NOx emissions.
Freeze frame data showing elevated NOx sensor voltage reading.
Associated SCR or emissions system DTCs stored alongside P24B3.

How to diagnose P24B3

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 upstream NOx sensor voltage and compare to manufacturer specifications.
  3. 3
    Inspect the NOx sensor harness and connector for shorts to voltage, chafing, or corrosion.
  4. 4
    Measure sensor signal circuit voltage with the connector disconnected to isolate a harness short from a sensor fault.
  5. 5
    If the harness is intact, replace the upstream NOx sensor and retest.
  6. 6
    If the fault persists after sensor replacement, inspect and test the NOx sensor control module.
  7. 7
    Clear DTCs and perform a complete drive cycle to confirm the repair.

Vehicles where we've handled P24B3

Platforms in our catalogue with confirmed P24B3 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I drive with P24B3 active?

Short-term driving is generally possible, but continued operation with a faulty NOx sensor can result in increased emissions, potential SCR system damage, and possible failed emissions inspections. Repair as soon as practical.

Will this code cause limp mode?

P24B3 alone typically does not trigger engine limp mode but may restrict SCR dosing. If accompanied by other SCR or reductant codes, more severe drivability limitations may occur.

How do I confirm it is a sensor fault and not a wiring fault?

Disconnect the sensor connector and measure the signal circuit voltage at the harness side. If voltage is still elevated with the sensor disconnected, the fault is in the wiring or PCM, not the sensor itself.

Does P24B3 always require sensor replacement?

Not always. A wiring short to voltage, a damaged connector, or a faulty NOx sensor module can cause the same fault. Diagnose the circuit fully before replacing the sensor.

Disabling P24B3 in software

RaceTune can permanently disable P24B3 — 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 P24B3 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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