P260B

Control Circuit Low

P260B is a generic OBD-II powertrain diagnostic trouble code: Control 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
P260B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P260B means

P260B is set when the SCR or ECM control module detects a low voltage or short-to-ground condition on the reductant injector control circuit for Bank 1. The reductant dosing injector sprays a precise quantity of DEF into the hot exhaust stream upstream of the SCR catalyst; accurate injector control is critical for achieving the NOx conversion chemistry and meeting emission standards.

A low circuit condition indicates the injector drive circuit is grounded when it should not be, which can result from a shorted injector solenoid winding, a short to ground in the wiring harness, or a failed driver stage in the SCR control module. An injector that is stuck open or shorted may inject DEF continuously, causing ammonia slip downstream, or the system may shut down dosing entirely to prevent damage.

Diagnosis should start with a visual inspection of the injector connector and harness. Measure injector solenoid resistance and compare with specifications. Check for a short to ground on the injector control wire before condemning the SCR module. A scan tool with actuator capability can be used to command the injector and observe driver behavior.

Common causes

Most-frequently reported root causes when P260B is logged.

  • 1
    Short to ground on the reductant injector control wire.
  • 2
    Failed injector solenoid with internal winding short.
  • 3
    Damaged wiring harness routed too close to exhaust heat.
  • 4
    Corroded injector connector causing tracking to ground.
  • 5
    Failed output driver in the SCR control module.
  • 6
    Injector clogged with crystallized urea causing solenoid stall and driver overload.
  • 7
    Moisture intrusion in the injector connector leading to a ground fault.

Symptoms drivers notice

MIL and SCR system warning lamp active.
Reductant dosing disabled, resulting in elevated NOx emissions.
Possible ammonia odor from the exhaust if the injector is stuck open before the fault is detected.
Engine derate or speed limiting after multiple non-repaired drive cycles.
Companion codes for SCR catalyst efficiency or NOx sensor out-of-range may appear.

How to diagnose P260B

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs with a scan tool before any repairs.
  2. 2
    Inspect the reductant injector connector, pigtail, and surrounding harness for heat damage or chafing.
  3. 3
    Measure the injector solenoid resistance between the two injector terminals; an out-of-specification low reading indicates an internal short.
  4. 4
    With the harness disconnected from the injector, measure the resistance of the control wire to ground; near zero ohms indicates a harness short.
  5. 5
    Verify injector supply voltage is correct with the ignition on.
  6. 6
    Use a scan tool actuator test to command the injector; confirm the module can drive the circuit correctly when a good injector and clean wiring are installed.
  7. 7
    Replace the injector or repair the harness as indicated, then retest.

Vehicles where we've handled P260B

Platforms in our catalogue with confirmed P260B coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Is P260B specific to diesel engines?

Yes, in practice. Reductant dosing injectors are components of diesel SCR emission systems and are not found on gasoline engines under normal circumstances.

Can urea crystallization damage the injector?

Yes. Urea crystallizes if DEF is not purged from a hot injector properly. A clogged or seized injector can cause the solenoid to stall, overloading the driver and triggering circuit faults.

How do I know if it is the injector or the module?

Disconnecting the injector and measuring the resistance of the control wire to ground will isolate a harness or injector fault from a module driver fault. A known-good injector can also be substituted temporarily.

Will P260B set immediately or after multiple cycles?

Most manufacturers set this code after detecting the circuit fault for a defined time, often within one drive cycle once the SCR system activates.

Disabling P260B in software

RaceTune can permanently disable P260B — 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 P260B 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

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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