P263B
Reductant Pump Motor Current HighP263B is a generic OBD-II powertrain diagnostic trouble code: Reductant Pump Motor Current High. 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 P263B means
P263B is stored when the ECM detects an abnormally high current draw from the SCR reductant pump motor. High current draw typically indicates the motor is working harder than expected due to a mechanical restriction in the DEF delivery system, a failing motor with increased internal friction, or a short circuit within the motor windings drawing excessive current from the supply.
Frozen DEF lines are a common seasonal cause of this code in cold climates, as the pump attempts to force fluid through a blocked circuit and the motor stalls, causing current to spike. DEF crystallization around the dosing injector or in the supply line can produce the same blockage effect. A motor with worn or shorted windings will also exhibit elevated current draw even without a physical restriction.
The ECM may cut power to the pump to protect the motor and control circuit when current exceeds safe limits. Extended high-current faults can damage the pump motor and the control circuitry. Diagnosis should address both the electrical condition of the motor and the possibility of a physical blockage in the DEF circuit before replacement.
Common causes
Most-frequently reported root causes when P263B is logged.
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1
Frozen DEF fluid blocking the supply line, injector, or pump.
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2
DEF crystallization causing a restriction in the pump or delivery circuit.
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3
Failed pump motor with shorted windings drawing excessive current.
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4
Mechanical seizure of the pump impeller due to contamination.
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5
Short circuit in the pump motor power wiring creating additional current paths.
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6
Faulty current-sense circuit reporting falsely elevated current.
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7
Blocked dosing injector creating backpressure that stalls the pump.
Symptoms drivers notice
How to diagnose P263B
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, record all related codes, and note ambient temperature at time of fault to assess freeze risk.
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2
Allow the vehicle to warm up if frozen DEF is suspected; verify the DEF tank heater is functional.
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3
Inspect the DEF supply line, dosing injector, and pump outlet for crystallization or physical blockage.
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4
With the pump commanded on via scan tool, observe live current data to confirm high current condition.
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5
Disconnect the pump and check motor winding resistance for signs of internal shorts.
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6
Inspect the pump wiring for shorts between motor supply and ground that could add current paths.
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7
Replace the reductant pump module if motor windings are shorted or the pump impeller is seized.
Related powertrain codes
Frequently asked questions
Is P263B common in winter?
Yes. DEF freezes at approximately -11 degrees Celsius and a pump attempting to push through frozen fluid is a very common cause of P263B in cold climates.
Does the DEF tank have a built-in heater?
Most diesel vehicles include an integrated DEF tank heater; if the heater fails, frozen DEF becomes a recurring fault source in cold weather.
Can I flush the DEF system to clear a blockage?
Yes. If DEF crystallization is the cause, flushing with deionized water (not tap water) per the manufacturer procedure can clear the restriction and resolve the code.
How urgent is P263B?
The SCR system is disabled when this fault is active, so NOx emissions will be elevated. A derate may follow within a defined period; repair should be completed promptly.
Disabling P263B in software
RaceTune can permanently disable P263B — 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 P263B 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 MD1CS001 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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