Quote:
Originally Posted by Saif2018
Juat wondering do the oscillations occur only on decattted cars and is there a reason why it doesn't occur in every car?
Many thanks for your input and help.
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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.