Hi All have got the following readings from my Mk3 punto(see pic) Car fully warmed up after 15 min. drive. It shows after cat lambda as being Open loop although it is showing a voltage, and says its on bottom limit,the pre cat is working ok flipping between rich and lean,car is running just fine,Has the after cat sensor failed?

Post cat lambda reports condition of cat, if there is a problem with cat or post cat lambda fault code should be logged.
If no fault code for lambda sensor 2 don't worry about it.

If you see post cat o2 sensor switching then its likely the cat isn't working.

The phrase open loop and closed loop is basically if the ecu reacts to the informatiom provided

Even if its open loop - most ecus will still recieve its signal from the sensor but it wont react to it the criteria is met

Since your on mes
You can do a graph readout - which will show 10x better what the sensors are doing

Go for a drive to get the car hot and then get the graph going

I would like to see the pre sensor zig-zagging going from lean to high alot

And post cat should also be reacting but not as fast less of s zig-zag more of a gentle wave

Ziggy

Turned out that the pipe just below the Cat(near o2 sensor) had a hole,which is now welded up!

texx said:

Turned out that the pipe just below the Cat(near o2 sensor) had a hole,which is now welded up!

Click to expand...

A hole or a crack?
As ive had my cat welded up 3 times now
1 around sensor lower and 1 at bottom on cat itself...

Ziggy