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      06-05-2022, 12:41 PM   #52
Saif2018
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Drives: E90 335i
Join Date: Jan 2019
Location: UK

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Quote:
Originally Posted by CarAbuser View Post
Because on decatted cars the diagnosis fails and will keep running.

It can happen on catted cars that have bad O2 sensors or bad cats.

The diagnostic routine manipulates the lamba target and looks for a proportional change in both up and downstream O2 sensors. It also looks at the lag in response along with a change in readings between the up and downstream sensors to work out how healthy the cat is.

These tests only occur at cruising and sometimes idle conditions. Once the engine is put under load they stop.
Many thanks you the explanation.
Appreciate 1
Dave92N54476.00