P25B6

Reductant Injection Valve Control Circuit Low

P25B6 is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Valve 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
P25B6
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P25B6 means

P25B6 is stored when the SCR control module detects a lower-than-expected voltage on the reductant dosing injector control circuit. A circuit low condition typically indicates a short to ground on the control wiring, an internal injector coil short to the injector housing, or a failed control module output driver that is pulling the circuit low when it should not be.

The module drives the dosing injector solenoid through a high-side or low-side driver. When a short to ground occurs on the control line, the driver detects excessive current or a collapsed voltage and stores this fault. The injector may be forced into a non-dosing state to protect the driver circuit from thermal damage.

Diagnosis requires careful isolation of the fault to either the wiring harness, the injector itself, or the control module. The wiring should be tested with the injector connector unplugged to determine whether the short is in the harness or inside the injector. Injector coil resistance should also be verified, as an internally shorted coil will appear as a circuit low fault.

Common causes

Most-frequently reported root causes when P25B6 is logged.

  • 1
    Short to ground on the reductant injector control wiring.
  • 2
    Chafed harness with insulation worn through allowing contact with chassis ground.
  • 3
    Failed dosing injector with internally shorted solenoid coil.
  • 4
    Corroded connector creating a leakage path to ground.
  • 5
    Failed control module output driver shorting to ground internally.
  • 6
    Incorrect injector installed with wrong coil resistance causing excessive current draw.

Symptoms drivers notice

MIL illuminated.
Reductant dosing inhibited by the control module.
SCR catalyst efficiency fault may develop secondary to dosing shutdown.
Engine torque derate after multiple drive cycles without repair.
No change in DEF fluid level indicating zero consumption.

How to diagnose P25B6

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze-frame data before clearing.
  2. 2
    Inspect the dosing injector harness and connector for chafed insulation, pinched wires, or corrosion.
  3. 3
    With the injector connector unplugged, measure resistance between the control circuit wire and chassis ground; a low reading indicates a harness short.
  4. 4
    Measure the injector solenoid coil resistance across the injector terminals and compare to specification; a low or zero reading indicates a shorted coil.
  5. 5
    If harness and injector are good, inspect the control module connector and check for the same short with the module connector also unplugged to isolate the module.
  6. 6
    Repair the identified short circuit or replace the injector if the coil is shorted.
  7. 7
    Clear codes and perform a DEF system function test to confirm normal operation.

Vehicles where we've handled P25B6

Platforms in our catalogue with confirmed P25B6 coverage.

BMW X5
2018–2019
BMW 530XD
2017
BMW 320D
2016
BMW 530XD 30D

Related powertrain codes

Frequently asked questions

What is the difference between a circuit low and circuit high code?

A circuit low code means voltage is below the expected range, most often caused by a short to ground. A circuit high code means voltage is above the expected range, most often caused by a short to a voltage source or an open return path.

Can I test for a short to ground with a regular multimeter?

Yes. Set the multimeter to resistance mode, connect one probe to the suspect wire and the other to chassis ground. A near-zero reading confirms a short to ground.

Will the injector be damaged by a short?

The control module typically limits current or shuts off the driver quickly when a short is detected, reducing the risk of injector damage. However, prolonged undetected shorts can overheat the driver and wiring.

Could water intrusion cause this code?

Yes. Water in the injector connector can create a conductive path to ground and cause intermittent or constant circuit low faults. Inspect the connector seal and replace if damaged.

Disabling P25B6 in software

RaceTune can permanently disable P25B6 — 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 P25B6 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 EDC17C56 verified 1 software version
  • Bosch MD1CP002 verified 1 software version
  • 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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