Error code

Error codes for exhaust gases – catalytic converter, OPF/GPF & downpipes at a glance

Exhaust-related error codes are among the most common causes of the engine warning light coming on. Systems relating to the catalytic converter (cat), petrol particulate filter (OPF), gas particulate filter (GPF) and downpipes (standard or tuning components) are particularly affected. Typical codes such as P0420, P0421 or P0430 often occur repeatedly – even after repairs or retrofits.

Why do cat/OPF/GPF errors return despite repairs?

  • Ageing/degradation of catalytic converter/OPF/GPF → altered conversion/filtration values
  • Sporadic measurement deviations from sensors (pre-cat/post-cat)
  • System effects after conversions (e.g. downpipes, exhaust systems, software adjustments)
  • Adaptations in the engine control unit that are not completely "re-learned"

The result is often the same: the MKL goes out – and comes back after a short time. This is exactly where our solution comes in.

The OBD killer as a permanent solution

The OBD Killer monitors the error memory in real time and blocks sporadic error codes relevant to exhaust emissions ( e.g. from the catalytic converter/OPF/GPF area) before they are even recorded. This keeps the engine warning light off, while unrecognised errors remain visible. The module is adaptive, fully automatic and suitable for almost all vehicles from 2008 onwards – ideal even after upgrades such as downpipes or exhaust system modifications.

Examples of common exhaust emission error codes

  • Catalytic converter: P0420, P0421, P0422, P0423, P0424, P0430, P0431, P0432, P0433, P0434
  • OPF/GPF & downpipes: recurring efficiency/threshold messages after modifications
  • Other relevant codes: P0400 – P0409 (EGR environment), P0234 (boost pressure control limit exceeded)

Detailed explanations of each code can be found in the individual blog articles in this category.

Frequently asked questions

What are typical catalytic converter error codes?

P0420 – P0424 and P0430 – P0434 are frequently reported. Among other things, they indicate reduced catalytic converter efficiency or measurement deviations.

What role do OPF/GPF and downpipes play?

OPF/GPF and downpipes alter flow, back pressure and measured values. After conversions, efficiency or threshold errors occur more frequently – even with otherwise intact hardware.

Why do part replacement or cleaning often only help for a short time?

This is because sporadic signals, ageing effects or software adaptations are not fully addressed. The error returns under similar conditions.

How does the OBD killer prevent recurring exhaust emission errors?

The module learns defined, exhaust-related codes and blocks them preventively before they are stored. Unlearned errors remain visible – the residual diagnosis is retained.

Does the OBD killer also work after downpipe or exhaust system conversion?

Yes. Especially after downpipes, OPF/GPF or software adjustments, the OBD killer is ideal for permanently preventing recurring MKL messages.

Is the OBD killer compatible with all vehicles?

For almost all vehicles from 2008 onwards. When changing vehicles, the module recognises the new chassis number and resets its learning values.

Does the OBD killer interfere with the engine control unit?

No. It is operated externally on the OBD port and does not modify the control unit.

Is there anything else I need to consider after installation?

Not usually – the OBD killer works fully automatically. Follow the installation instructions and local regulations.

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