High CO MOT problem! Oxygen sensor defect or... ?

[HJ2]

Dear all,

During my last MOT the strangest thing happened:

With the O2 sensor in place, and the engine HOT, the CO % at idle was around 2,7%
With the sensor unplugged (so map based mixture only) the CO % dropped to 0.35!
(without any CAT)

Doe this mean that my sensor is faulty or that i have a leak in the exhaust somewhere around the O2 sensor, or does this imply another failure somewhere?
Is there a way to check if the current O2 sensor is functioning within specified band width? (for instance with elanscan)...

Any help appreciated!

[GeoffSmith]

ES logs the O2 output voltages and indicates open/closed loop operation.

[HJ2]

Thanks geoff.

What voltage should I expect at idle?
I now read 0,3v ... 3,6v and it jumps all over with a cold engine.
Oxygen Integrator says 88 and later on 8A(?)
Knock counter is high allready :61!

[HJ2]

Small update:

I took the plunge and removed the down-pipe again.
It looks like the seal between turbo and down-pipe is questionable, but even worse: there is a leak in one of the welds from the down-pipe (NOT a piper weld, but one from my welder)
This leak is only 2 cm. away from the O2 sensor.

Could this cause my high CO?
(it's out now, ready for welding again)...

[HJ2]

Okay..

I see that I wrote CO2, where i meant CO!
Down-pipe leak is welded up, and I replaced the gasket to the turbo flange. Everything reassembled now, after I warmed up the Elan I tested again:

Hot engine @ Idle:
0,86% CO
13,54% CO2
Lambda 1.038
1,50% vol O2

Unplugging the O2 sensor did not change anything @ Idle anymore, so that's an improvement... But the value of 0.35% CO open loop disappeared as well!
However I unplugged the O2 sensor with a running engine this time, should I have restarted it first?

so, a lot better, but I still aim at 0.45% CO with the O2 sensor in closed loop.

Also Elanscan shows:
PROM Error (?)
Manifold Pressure 0.35 bar (is this okay-ish?)
Spark advance = 17
Oxygen Sensor varies between 0,4 ... 3,5

How / where in Elanscan can i see if the car runs closed loop or not?

[GeoffSmith]

Flag 42 bit 0

[HJ2]

OK!