How to pass the technical inspection with a modified exhaust?

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Introduction

You have installed a sports exhaust on your car: stainless steel line, decatalyst, sports catalytic converter or remote-controlled flaps. The result is there: more muscular sound , reduced weight , increased responsiveness ...

But one question comes up as the fateful deadline approaches:
“Will I pass the technical inspection with this?”

Don’t panic. In this blog, we explain:

• Current technical inspection rules

• What is tolerated , what is not recommended , and what is blocking

• Tips for anticipating problems

• Rog 's smart solutions for driving freely without giving up the MOT

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Technical inspection: what it checks on the exhaust

Technical inspections in France have become more stringent in recent years, particularly with regard to emissions and noise.

On the exhaust line, here is what is examined:

🔍 1. Leaks or visible deterioration

• Cracked, pierced line = re-inspection

• Poorly made welds or visible adaptation = minor/major remark or defect

🔍 2. Presence and good condition of the catalyst

• If the vehicle is approved with a catalyst ➜ it must be present

• Absence = major defect ➜ refusal of the CT

• Inspectors are trained to recognize a decatalyst

🔍 3. Pollution level

• CO, HC, NOx levels measured by the gas analyzer

• Too high ➜ CT refusal

• Decatalytic converter = often non-standard rate (except very clean engines)

🔍 4. Sound level

• Still little controlled via sound level meter, but:

  • The sound is evaluated “by ear”

  • If deemed “abnormally high” ➜ comment or re-inspection

🔍 5. Engine light

• Engine light on = major fault

• It must be turned off with the engine running

• Often linked to a modified line (decata without reprogramming)

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Does a modified exhaust pass the MOT?

🟢 YES, if:

• You have a sport catalyst (300 or 200 cells)

• You have a valve line , in the closed position

• The engine light is off

• The line is well laid , without leaks or rough assembly

🔴 NO, if:

• You have a permanent decatalyst

• You have an engine light on

• The sound is considered abnormally high

• The installation is clearly non-compliant

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What solutions are there to stay calm?

✅ 1. Opt for a sports catalyst

The sports catalyst allows you to:

• Reduce emissions

• Keep a filter function

• Maintain a smooth and efficient line

• Reduce the sound to stay under the radar

At Rog , we offer:

• 300-cell sport cat ➜ ideal for MOT

• 200-cell sports cat ➜ good compromise

• 100-cell catamaran ➜ more efficient, but to be checked according to the engine

💡 In any case, it is better to reprogram the ECU to avoid lambda sensor errors.

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✅ 2. Use remote-controlled flaps

The valves allow:

• To close the sound channel before the CT

• To drastically reduce the volume

• To have a “compliant” mode and a “pleasure” mode to choose from

At Rog , our flap lines are:

• Controllable by remote control or mobile app

• Designed to remain discreet when necessary

• Compatible with sport or decatalytic converters depending on your use

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✅ 3. Temporarily return to the original configuration

For the purists:

• It is possible to refit the original catalytic converter before the MOT

• To temporarily disable Pop & Bang or sports maps

Attention :

• It requires manpower, time, organization

• Favor removable assemblies (collars, Rog bridles)

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✅ 4. Hide the engine light

Temporary and questionable solution:
Some people turn off the engine light without correcting the cause ➜ not recommended.

The best:

• Reprogramming with clean deactivation

• Or use of a probe simulator (depending on compatibility)

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What's Risky (and How Rog Keeps You Out of It)

❌ Homemade welded line

• Bad alignment = leaks

• Controller = immediate notice

✅ Rog lines : perfectly adjusted, easy assembly, clean finishes

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❌ Permanent decatalytic converter without card

• Engine light

• Pollutants on the ceiling

✅ Rog : decata + reprog = coherent combo. Or 200/300c sport cat for the compromise.

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❌ Line too noisy

• Non-existent flaps

• Noise when starting or stopping

✅ Rog : adapted silencers + valves = closed mode CT-friendly

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Special case: decatalyzed line

A pure and hard decatalyst, even discreet, is visually identifiable :

• Straight tube

• Empty location or with "too clean" tube

• No original welding

👉 At Rog , we recommend:

• Do not use a decatalytic converter on the open road

• To consider a removable line

• To couple this with a complete reprogramming

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Customer Testimonials

"Decat line + Rog valves. I close everything for the MOT, no problem. The rest of the time, it's fire."

"I opted for a 200-cell sport catamaran from Rog. It passed the inspection, and the sound remains very deep."

"With the flaps closed, even my M2 remains discreet during inspection. I've never had any comments."

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In summary: what happens / what blocks

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What does Rog suggest for driving freely and passing the MOT?

• ✅ Sport catalysts 100 / 200 / 300 cells

• ✅ Remote-controlled flap lines

• ✅ Modular and removable systems

• ✅ Quality materials (stainless steel, titanium)

• ✅ Lambda probe compatibility retained

• ✅ Technical support to help you choose the right one

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Conclusion

Modifying your exhaust does not prevent you from passing the technical inspection — provided you are properly equipped .

With intelligently designed solutions, you can:

• Enjoy racing sound

• Gain in power and lightness

• And stay within administrative limits

Rog helps you combine passion and peace of mind with evolving, tailor-made lines that are compatible with everyday constraints.