P24EB

NOx Sensor Circuit Low (Bank 1 Sensor 2)

P24EB is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Circuit Low (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
P24EB
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24EB means

P24EB is stored when the ECM detects that the NOx sensor signal voltage on Bank 1, downstream position (Sensor 2), has fallen below the expected operating range for a sustained period. This sensor monitors the NOx content of exhaust gas exiting the SCR catalyst and provides the feedback signal used to evaluate SCR conversion efficiency and to control reductant dosing.

A low circuit condition typically indicates an open circuit in the sensor wiring harness, a shorted signal wire, a failed sensor heater causing the sensor to stay cold, or an internal sensor cell failure. The ECM uses this signal to assess whether the selective catalytic reduction system is performing within regulatory limits, so a fault here can trigger an SCR system shutdown and associated emission-related codes.

Before replacing the sensor, inspect the connector and wiring harness for damage, corrosion, or chafing. Verify the sensor heater circuit is functioning, as a cold NOx sensor will output abnormally low voltages. Use a scan tool to check live NOx sensor data and compare both upstream and downstream readings during a warm, steady-state drive cycle.

Common causes

Most-frequently reported root causes when P24EB is logged.

  • 1
    Open circuit or broken wire in the NOx sensor signal circuit.
  • 2
    Corroded or damaged sensor connector causing high resistance.
  • 3
    Failed NOx sensor heater element leaving the sensor below operating temperature.
  • 4
    Internal failure of the downstream NOx sensor electrochemical cell.
  • 5
    Short to ground on the sensor signal wire.
  • 6
    ECM internal fault affecting the NOx sensor input channel.
  • 7
    Exhaust system leak upstream of the sensor causing abnormal gas composition readings.

Symptoms drivers notice

MIL illuminated with P24EB stored.
SCR system may enter reduced or disabled dosing mode.
Possible increase in NOx emissions without a noticeable driveability change.
Additional SCR or reductant fault codes may accompany this code.
OBD readiness monitor for the catalyst may fail.

How to diagnose P24EB

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored DTCs before clearing anything.
  2. 2
    Check live NOx sensor data for Bank 1 Sensor 2 at idle and during a drive; a reading stuck near zero or minimum indicates a circuit or sensor fault.
  3. 3
    Inspect the sensor connector, pigtail, and wiring harness for damage, corrosion, or chafing against hot exhaust components.
  4. 4
    Measure the sensor heater resistance and verify the heater supply circuit; a cold sensor will output a low signal.
  5. 5
    Perform a voltage drop test on the signal and reference circuits between the sensor and ECM.
  6. 6
    If wiring and heater check out, replace the downstream NOx sensor and retest.
  7. 7
    Clear codes and run an OBD drive cycle to confirm the fault does not return.

Vehicles where we've handled P24EB

Platforms in our catalogue with confirmed P24EB coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can I drive with P24EB active?

Short-term driving is generally possible, but the SCR system may be disabled, increasing NOx emissions. Have the fault diagnosed promptly to avoid regulatory non-compliance and potential additional faults.

Is P24EB the same as a general O2 sensor code?

No. A NOx sensor measures nitrogen oxide concentration using an electrochemical cell and operates differently from a conventional wideband or narrowband oxygen sensor, though both produce voltage signals the ECM monitors.

Could a bad DEF quality cause P24EB?

Poor DEF quality affects SCR efficiency but typically sets different codes. P24EB specifically indicates a circuit-level fault with the sensor itself, not a quality or concentration issue.

Does P24EB always mean I need a new sensor?

Not necessarily. A damaged wiring harness, corroded connector, or failed heater circuit can cause this code. Always inspect the wiring and verify the heater before condemning the sensor.

Disabling P24EB in software

RaceTune can permanently disable P24EB — 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 P24EB 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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