P255F
Reductant Level Sensor Circuit LowP255F is a generic OBD-II powertrain diagnostic trouble code: Reductant Level 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.
What P255F means
P255F is set when the ECM or SCR control module reads a voltage on the DEF/AdBlue level sensor circuit that is below the minimum calibrated threshold. The reductant level sensor monitors fluid quantity in the DEF tank, allowing the system to warn the driver before the tank runs empty and ensuring SCR operation is only enabled when sufficient reductant is present.
A circuit low condition most often indicates a short to ground in the sensor signal wire, a failed sensor with an internally grounded output, or a broken sensor ground that shifts the reference point. The fault may also appear if the tank is completely empty on vehicles where the sensor bottoms out below the lowest valid reading, so DEF level should be checked before electrical diagnosis begins.
Wiring near the DEF tank can be exposed to moisture and road debris, making connector corrosion and harness damage common causes. Inspect the sensor connector and wiring routing carefully before condemning the sensor itself.
Common causes
Most-frequently reported root causes when P255F is logged.
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1
Short to ground on the level sensor signal wire.
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2
Failed reductant level sensor with internally shorted output.
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3
Open or corroded sensor ground connection altering reference voltage.
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4
Water or DEF ingress into the sensor connector causing corrosion.
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5
Damaged wiring harness along the tank-to-module routing.
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6
Completely empty DEF tank driving sensor below its valid range on some designs.
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7
Faulty SCR control module input circuit.
Symptoms drivers notice
How to diagnose P255F
A typical diagnostic flow when this code is present.
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1
Check DEF level first; refill if empty to rule out a dry-tank sensor floor condition.
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2
Read all DTCs and check for companion sensor or SCR codes.
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3
Inspect the level sensor connector and wiring for corrosion, moisture, and damage.
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4
With ignition on and sensor connected, measure signal voltage and compare to specification.
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5
Unplug the sensor and measure signal wire voltage to ground to check for a short to ground.
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6
Measure sensor supply voltage to confirm the module is providing correct reference voltage.
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7
Replace the sensor if wiring checks out and the signal remains out of range.
Vehicles where we've handled P255F
Platforms in our catalogue with confirmed P255F coverage.
Related powertrain codes
Frequently asked questions
Can adding DEF clear P255F?
If the fault was caused by the tank being empty and the sensor reaching its lower limit, refilling DEF may clear the code, but verify by checking for wiring faults as well.
Does P255F mean my DEF tank sensor is definitely bad?
Not necessarily; wiring shorts to ground and connector corrosion are equally common. Perform circuit testing before replacing the sensor.
Will P255F trigger a power de-rate?
Some vehicles will initiate a torque reduction if the DEF level cannot be confirmed, so the fault should be repaired promptly.
Is the level sensor part of the DEF pump module?
On many modern vehicles the level sensor, temperature sensor, and quality sensor are integrated into the DEF tank module alongside the pump; they may be serviced as an assembly.
Disabling P255F in software
RaceTune can permanently disable P255F — 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.
ECUs with a P255F 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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