Polo 9n AZQ pre cat o2 sensor

[Psion]

Hi all

I have full VCDS and have a problem with my daughters Polo, I could not get the pre cat O2 sensor to do an ageing check, it refused to move from test off, although it does seem to flicker from time to time.

So far I have tested that there are 3.5 ohms between terminal 3 and 4 on the O2 sensor and have 100ohms resistance between terminals 6 and 1, I also have open circuit between the other terminals from 3 and 4 and the casing, I have power at terminal 3 on the wiring harness and I have checked for continuity on terminal 3, I have also checked the voltage on terminals 6 and 1 which varies between 0 and .45 volts i.e. what you would expect.

I have removed j121 (ECU connection) and checked for corrosion, there wasn't any but still gave it a squirt of contact cleaner and checked continuity on terminal 4 as belt and braces and still the test off refused to budge, so bit the bullet and bought a genuine VW precat O2 sensor, I again checked this with a multi-metre and still the test off will not budge.

Fuse 9 is fine.

I am out of ideas, please help as the MOT is due soon and took it down today as I know the guy and it failed on CO2 .5, .2 is the pass.

At the moment I have no engine light and the only codes I have had recently was a G62 implausible signal (it is a green sensor), I have just taken it for an Italian tune up, I still have no codes, but on the readiness both O2 fail or not passed, heating ok in both and the CAT is fail or not passed.

That's something else on the CAT test it just stays in the test on, i held that for a good 5 minutes and it never changed from test on

My dilemma is do I take a punt on a new CAT, or could it be something I haven't thought of, hence this long post.

thanks all

[rowdy-999]

So whats the actually wrong with the car?

[Psion]

The pre cat O2 sensor will not go into the ageing test and the car is running slightly rich, which is causing it to fail the emissions test on Co2.

[34stuey]

Suggest you try ‘Cataclean‘ to clean the Catalytic converter, unlikely to resolve the Lambda sensor issue but may help to resolve the high CO reading. Had a similar problem on my 55 plate Polo SE 1.4 BKY engine and the cleaner reduced the CO reading from.44 to approx .25. Apparently the cleaner is only a temporary fix as it’s likely the Cat is damaged beyond repair. Likely the car has been used for short journeys resulting in a film build up on the active precious metal in the Cat.

[Crasher]

The cats on the AZQ have always been unreliable, some of the aftermarket ones I have been supplied were so badly made I sent them back. One I was sent many years ago when the problem became common was fabricated from flat sheet steel and pigeon **** MIG welded together in square section; it was so ugly it was beyond words, I wish I had taken a picture.