18.Nov.2025 - P0407 – Causes, Diagnosis & Permanent Solution with OBD-Killer

What does P0407 mean – and why does the error often recur?

P0407 stands for "Exhaust Gas Recirculation (EGR) Sensor B Circuit Low" – a signal that is too low in the EGR sensor "B" circuit. The engine warning light often comes on even though the vehicle is still running normally. After cleaning, replacing parts or modifying the exhaust system, the message often reappears.

Typical causes & diagnostic pitfalls

  • Undervoltage, ground fault or signal interruption in sensor "B" circuit
  • Defective EGR sensor/EGR valve (potentiometer worn, position feedback faulty)
  • Corrosion, loose connection or broken cable on plugs or wires
  • Coked EGR channels → position deviations, sporadic sensor dispersion
  • Changed flow conditions after OPF/GPF/cat conversions

Practical tip: The valve is often replaced – but if the electrical cause or a system effect persists, P0407 will return.

Why repairs are not a permanent solution

  • Sporadic measurement deviations trigger the code again despite new parts
  • Adaptation/software values are not relearned
  • System effects due to conversions remain unchanged

OBD Killer – the only solution that permanently stops P0407

The OBD Killer is plugged into the OBD diagnostic port and monitors the fault memory in real time. Sporadic, exhaust-related codes such as P0407 are blocked before they are stored. Other faults remain visible.

  • Adaptive and automatic – intervention before error entry
  • Universal for almost all vehicles from 2008 onwards
  • Ideal after exhaust retrofits and for recurring MKL

Frequently affected brands

Particularly common for VW/Audi, Ford, BMW/MINI and Mercedes-Benz – the OBD Killer solution works identically across all manufacturers.

Practical example

After EGR cleaning and a new sensor "B", P0407 returned after a few days. With the OBD killer installed, the engine warning light remained off – without any further parts replacement.

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Frequently asked questions

What exactly does error code P0407 mean?

P0407 indicates a low signal in the EGR sensor "B" circuit (EGR Sensor B Circuit Low).

What symptoms occur?

In most cases, the engine warning light comes on; occasionally, there is increased fuel consumption or a slight loss of power.

What are the most common causes?

Undervoltage/ground fault, defective sensor/valve, corrosion/breakage, coking, conversion effects.

Can I clear the error myself?

Yes – but usually returns if the cause persists.

Why does P0407 reappear despite repairs?

Because system effects and sporadic signal deviations are not remedied by replacing parts.

Does EGR cleaning help permanently?

Only if there are no electrical causes. Otherwise, P0407 will reoccur.

Does the OBD killer interfere with the control unit?

No, it works externally on the OBD port and does not modify the engine control unit.

Use after repair – is this advisable?

Yes, ideal for recurring EGR faults such as P0407, especially after conversions.

Will the OBD killer work on my vehicle?

Suitable for almost all vehicles from 2008 onwards; it resets its learning values when the vehicle is changed.

How do I order the OBD killer?

Via the product page below – fast shipping, easy installation.

Conclusion

P0407 is a typical EGR fault that often recurs after repairs. The OBD killer offers the only permanent solution for reliably keeping the MKL under control – with full visibility of other faults.

Find out more about the OBD Killer on the home page.



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