P24E8

Reductant Tank Temperature Sensor Circuit Low

P24E8 is a generic OBD-II powertrain diagnostic trouble code: Reductant Tank Temperature Sensor Circuit Low. 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
P24E8
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24E8 means

P24E8 is set when the ECM detects that the signal from the DEF (reductant) tank temperature sensor is below the expected minimum voltage threshold. The tank temperature sensor is used to determine whether the DEF is frozen and to control the tank heater operation. Without accurate temperature data, the ECM cannot properly manage the DEF heating strategy.

A circuit-low fault typically indicates a short to ground in the sensor signal wire, an open reference voltage circuit, or a failed sensor with an internal short. In most implementations, the temperature sensor is a negative-temperature-coefficient (NTC) thermistor, and a short to ground on the signal wire will drive the voltage to near zero, which the ECM interprets as an impossibly high temperature or detects as out-of-range low voltage, depending on calibration.

When this fault is active, the ECM may default to a fixed temperature assumption for the DEF tank, which can cause improper heater operation. In cold climates, this can result in frozen DEF going undetected and SCR system failure. Diagnosis should focus on signal wire continuity, reference voltage presence, and sensor resistance before replacement.

Common causes

Most-frequently reported root causes when P24E8 is logged.

  • 1
    Short to ground on the temperature sensor signal wire.
  • 2
    Open circuit on the 5V reference voltage supply to the sensor.
  • 3
    Failed DEF tank temperature sensor with internal short.
  • 4
    Corroded or contaminated sensor connector causing low resistance path to ground.
  • 5
    Wiring harness damage near the DEF tank routing.
  • 6
    ECM reference voltage supply fault.

Symptoms drivers notice

MIL illuminated.
DEF system warning indicator may be active.
Improper DEF heater operation in cold conditions.
SCR system may fail to activate in freezing temperatures due to frozen DEF.
No drivability impact in warm ambient conditions.

How to diagnose P24E8

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all DTCs; check freeze frame for ambient temperature at fault set.
  2. 2
    Inspect the DEF tank temperature sensor connector and wiring for damage or corrosion.
  3. 3
    Measure the sensor signal voltage with the connector connected and ignition on; near-zero voltage confirms circuit-low.
  4. 4
    Disconnect the sensor and measure signal wire voltage; if it rises to near 5V, the sensor is internally shorted.
  5. 5
    Measure resistance of the sensor at ambient temperature and compare to NTC characteristic curve if available.
  6. 6
    Inspect the 5V reference supply wire at the ECM connector for continuity.
  7. 7
    Replace the sensor if it is internally shorted and wiring checks are normal.

Vehicles where we've handled P24E8

Platforms in our catalogue with confirmed P24E8 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

What happens if the DEF tank temperature sensor is ignored?

In warm weather the impact is minimal, but in freezing conditions the ECM loses the ability to detect or prevent DEF freezing. This can prevent SCR system activation and lead to NOx derate cycles.

Is P24E8 always a failed sensor?

No. A short to ground in the signal wiring will produce the same circuit-low symptom. Disconnecting the sensor and re-measuring the circuit voltage is the fastest way to distinguish a wiring fault from a sensor fault.

Can DEF contamination cause this code?

Yes. DEF leaking into the sensor connector can create a conductive path that drives the signal voltage low, mimicking a sensor or wiring short.

Will the DEF heater stop working with P24E8?

Heater behavior depends on ECM calibration. Some systems default to continuous heating when temperature feedback is lost; others disable the heater. Either can be problematic depending on ambient conditions.

Disabling P24E8 in software

RaceTune can permanently disable P24E8 — 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 P24E8 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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