When does a car fail its MOT?

If a car is fitted with a  Decat downpipe , it will fail its MOT. This is because the catalytic converter is visually missing, which the inspector will notice because there is no catalytic converter present. You can have the second lambda sensor deregistered by a  chip tuner  to drive without any issues, but the car will still fail its MOT without a catalytic converter.

A downpipe with a 100-cell high-flow CAT has 100 fewer cells than a 200-cell CAT. This means the flow, and therefore the airflow, is even better than with a 200-cell CAT. However, emissions issues can occur more frequently with a 100-cell CAT. Fortunately, the four-gas test is no longer mandatory for petrol cars after 2012, meaning cars with a 100-cell CAT can still pass their MOT. However, no check engine light should be illuminated.

How do I get my car through the MOT?

There are several methods used in practice. For example, you can install a  downpipe  with a 200-cell high-flow catalytic converter, which in the Netherlands is MOT-approved. However, it's important to note that the 200-cell catalytic converter allows significantly more airflow than the original catalytic converter. The problem with this is that you can still get an engine light (not always) because the second oxygen sensor doesn't detect a functioning catalytic converter. The catalytic converter is working, but the second oxygen sensor doesn't see it due to the much higher airflow. To make this engine light disappear, you can go to a  chip tuner  who can deregister the second oxygen sensor. Deregistering the second oxygen sensor has no negative consequences for power, safety, etc. This is purely a check to see if the catalytic converter is working.

Another method used is for people to drive around with a "Decat Downpipe" year-round and replace it with the original downpipe during the inspection, which of course does have a catalytic converter. To drive smoothly with a  Decat Downpipe  , however, you must ensure that the second lambda sensor has been deregistered by a  chip tuner .

Are there any more tricks?

The well-known lambda spacer / lambda fix / Cel Fix / Cellfix is ​​an extension of the lambda connection, sometimes incorporating a small catalytic converter. This spacer is intended to be placed between the lambda sensor and the nut on the exhaust, preventing the car from displaying a malfunction indicator light when a Decat downpipe / high-flow cat downpipe is installed (in some cases). However, in my experience, this doesn't work nine times out of ten. I've tested it on several cars with a lambda spacer, a small catalytic converter, a small catalytic converter, a bend, or a bend, and it almost never works. We don't want to mislead anyone and therefore don't sell this product.

This blog covers petrol cars from before 2019 (NON-OPF).
Please note that this is only advice; we assume no responsibility.

Posted on 23-22-2023 by Juul, JT-Products.