P261B

Pump B Control Circuit Range/Performance

P261B is a generic OBD-II powertrain diagnostic trouble code: Pump B Control Circuit Range/Performance. 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
P261B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P261B means

P261B is set when the ECM detects an abnormally high voltage or current reading on the control circuit for the SCR (Selective Catalytic Reduction) reductant (DEF/AdBlue) pump motor. The reductant pump is responsible for pressurizing the DEF supply line and delivering the correct dose of urea solution to the SCR catalyst to convert NOx into harmless nitrogen and water.

A high-circuit condition typically indicates a short to a voltage source in the pump motor control wiring, a failed pump motor that is drawing excessive current, or an internal fault in the ECM driver stage. Because proper SCR dosing is required to meet emissions regulations, the ECM treats reductant delivery faults seriously and may initiate a torque or speed dereate after a defined number of failed drive cycles.

Diagnosis should begin with a visual inspection of the DEF pump module and its wiring harness, followed by electrical measurements to isolate whether the fault is in the wiring, the pump motor assembly, or the control module. DEF contamination can also corrode connector pins and create resistive or short-circuit faults.

Common causes

Most-frequently reported root causes when P261B is logged.

  • 1
    Short to battery voltage in the reductant pump motor control wire.
  • 2
    Failed reductant pump motor drawing excessive current.
  • 3
    Corroded or shorted wiring harness connector at the DEF pump module.
  • 4
    DEF fluid ingress into the pump electrical connector causing a short circuit.
  • 5
    Faulty ECM/DCM driver circuit for the pump motor output.
  • 6
    Incorrect aftermarket pump motor with incompatible resistance characteristics.
  • 7
    Chafed pump motor wiring contacting a battery-positive source.

Symptoms drivers notice

MIL illuminated along with a diesel emissions warning lamp.
SCR system inactive or reduced DEF dosing.
Vehicle torque derate or speed limiter active after extended fault period.
DEF pump may not prime or pressurize the supply line.
Increased NOx emissions detectable on a gas analyzer.

How to diagnose P261B

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, record all DTCs and freeze-frame data, and note SCR system live data parameters.
  2. 2
    Inspect the DEF pump module and its wiring harness for DEF crystallization, corrosion, or physical damage.
  3. 3
    Disconnect the pump connector and measure supply voltage and ground integrity at the harness side.
  4. 4
    Check for unwanted voltage on the pump motor control wire with the connector unplugged to identify a short to power.
  5. 5
    Measure the resistance of the pump motor across its terminals and compare to manufacturer specifications.
  6. 6
    Perform a functional test of the pump via scan tool if available to observe current draw.
  7. 7
    Replace the reductant pump module if motor resistance or current draw is out of specification.

Related powertrain codes

Frequently asked questions

How long before the engine is derated with P261B?

Derate timing varies by manufacturer but most diesel systems allow a window of several drive cycles or a defined mileage before applying a torque or speed reduction.

Can a frozen DEF tank cause P261B?

DEF freezing can prevent pump operation and may cause related faults, but P261B specifically points to a high-circuit electrical condition rather than a fluid delivery issue alone.

Is the DEF pump part of the tank module?

On most vehicles the DEF pump is integrated into the tank module along with a heater and level sensor; replacement typically involves the entire module.

Will topping up the DEF tank clear this code?

No. P261B is an electrical circuit fault and is not resolved by adding fluid.

Disabling P261B in software

RaceTune can permanently disable P261B — 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.

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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