P24BD

NOx Sensor Heater Control Circuit Bank 1 Sensor 1

P24BD is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Heater Control Circuit 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
P24BD
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24BD means

P24BD is stored when the PCM or NOx sensor control module detects a fault in the heater control circuit for the upstream NOx sensor (Bank 1, Sensor 1). NOx sensors contain an internal ceramic heater element that must reach a precise operating temperature before the electrochemical sensing cell can function accurately. Without proper heater operation the sensor output is unreliable.

The heater circuit is typically controlled by a pulse-width-modulated (PWM) signal from the sensor control module. The module monitors heater current and resistance to verify correct operation. A fault is flagged when the measured heater current or circuit feedback falls outside the expected window, which can indicate an open heater element, a short in the heater wiring, or a driver fault inside the control module.

When P24BD is active, the NOx sensor may not reach operating temperature in time, causing the SCR dosing strategy to default to a conservative or open-loop mode. The MIL is illuminated and repeated confirmed occurrences may set additional SCR-related codes. Repairing the heater circuit or replacing the sensor typically resolves the fault.

Common causes

Most-frequently reported root causes when P24BD is logged.

  • 1
    Open circuit in the NOx sensor internal heater element.
  • 2
    Short to ground or to battery voltage in the heater supply or control wire.
  • 3
    Faulty NOx sensor control module heater driver circuit.
  • 4
    Corroded or damaged sensor connector affecting heater circuit continuity.
  • 5
    Broken heater wire in the sensor harness due to vibration fatigue.
  • 6
    Blown fuse in the heater supply circuit.
  • 7
    Water ingress into the sensor or connector damaging the heater element.

Symptoms drivers notice

MIL illuminated.
NOx sensor slow to reach operating temperature on cold starts.
SCR system in default or open-loop dosing mode.
Possible increased emissions during cold operation.
Additional SCR or NOx sensor rationality codes stored concurrently.

How to diagnose P24BD

A typical diagnostic flow when this code is present.

  1. 1
    Record all stored DTCs and freeze frame data before beginning diagnosis.
  2. 2
    Inspect the heater supply fuse for the NOx sensor circuit and replace if blown.
  3. 3
    Check the heater circuit wiring between the sensor and control module for opens, shorts, and chafing.
  4. 4
    Measure heater circuit resistance at the sensor connector and compare to specification.
  5. 5
    Verify the control module is supplying a PWM heater signal using an oscilloscope or scan tool if supported.
  6. 6
    If wiring and fuse are intact and the module output is correct, replace the NOx sensor.
  7. 7
    Clear codes and perform a cold-start drive cycle to confirm the heater reaches operating temperature.

Vehicles where we've handled P24BD

Platforms in our catalogue with confirmed P24BD coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Will P24BD prevent the NOx sensor from working at all?

A complete heater failure will prevent the sensor from reaching operating temperature, making the NOx reading unreliable. A partial fault may allow some operation but with delayed or inaccurate readings.

Is the heater inside the sensor replaceable separately?

No. The heater element is integral to the NOx sensor assembly and cannot be serviced separately. If the heater element is open, the entire sensor must be replaced.

Can a blown fuse cause P24BD?

Yes. If the heater supply fuse is blown, the heater will not receive power and the control module will detect the open circuit, setting P24BD.

How do I distinguish a sensor fault from a wiring fault?

Measure heater element resistance directly at the sensor connector with the harness disconnected. If resistance is open or far outside specification, the sensor is faulty. If resistance is correct but the circuit shows a fault, inspect the wiring and control module.

Disabling P24BD in software

RaceTune can permanently disable P24BD — 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 P24BD 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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