Lambda / O2 sensor removal

Lambda sensors tell the ECU how much oxygen is in the exhaust so it can hold the
fuelling where it needs to be. Modern cars have them before and after the catalyst, and
the rear one exists mainly to check the catalyst is working.

A failed sensor gives you poor economy, a fault code and a failed emissions test. They
are a wearing part, they are not expensive, and replacing one is a straightforward job.
That is the fix in nearly every case.

What we would rather do first

Most of the cars that arrive asking for removal do not need it. They need the
underlying fault finding and fixing, and the system putting back into a working
state. That is diagnostics, and it is a real service rather than a way of hiding a
warning light.

We have the diagnostic equipment and the rolling road to prove a repair worked
rather than assume it did. If a repair is not viable and the vehicle is genuinely
off road, export or competition, we will talk about the alternative.

The legal position, stated plainly

It is an offence in the UK to use a vehicle on the road with its emissions
control equipment removed or defeated. Since 2014 the MOT test includes a visual
check, and a missing filter is an automatic failure. Insurers can and do treat it
as an undeclared modification.

We say this on every page because we would rather lose the job than have a
customer find out at their next MOT. If your car is a road car, the answer is
repair, and we are set up to do that properly.

Where removal is legitimate: vehicles used solely
off the public road, competition vehicles, plant and agricultural machinery, and
vehicles being exported to territories with different requirements. We ask which
applies before we quote.

Catalytic converters: the same job under another name

People ask for a catalyst removal as though it were separate work. It is not. The
converter is monitored by the lambda sensor behind it, so taking the cat off and
deactivating that rear sensor are the same job described from two ends.

They fail in three ways: the substrate breaks up, usually because the engine has been
running badly and dumping fuel into it; it gets contaminated by oil or coolant from a
failing engine; or it is simply worn out and no longer converting enough to satisfy the
rear sensor. There is a fourth possibility that is not a fault at all, which is that
somebody has stolen it for the metals inside.

An efficiency code very often means the converter is fine and something before it is
wrong: a misfire, a leaking injector, or an exhaust leak drawing air in ahead of the
sensor. Fitting a converter without checking those is how people end up fitting two.

For the trade

This is one of the jobs available through our dealer file service. Send the
original read, tell us the vehicle and what you need, and the file comes back
checked. If a job carries mechanical conditions on the car, they are listed in the
coverage table below and they apply to your customer’s vehicle too.

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