2002 Polo 9N with AZQ motor (= 1.2 12v)

When presenting my car for the official yearly technical control here in Belgium I received a red card for the exhaust emission. I see on the official document I should have a lambda value between 0,97 and 1,03. The report does not give me the value measured, so no idea if it was higher or lower.

In VCDS I can see several lambda values in more then one of the measuring blocks 030..049 of the motor. However, although they are all called 'lambda', they give different readings. Does anyone has an idea if using VCDS the lambda value can be read out that the controlling organism is measuring through the analysis of the exhaust gas and the end of the exhaust pipe ?

Additional info and action meanwhile done:

The car had been out for almost a year due to an issue with the timing chain which had jumped (another thread in this forum). I just repaired it and changed oil + put a new oil filter. After resetting all 'chain jumped' related DTC's I had no errors re-appearing.

After presenting my car at the control organism and driving for about 10km, I had 2 error codes:

- 16555 : Fuel Trim; Bank 1: System Too Lean / P0171 - - - Intermittent
- 17658 : Fuel Level Too Low / P1250 - 35-00 - -

Some time already I have more then a suspicion that 1 or both of the oxygen sensors (before or after the catalytic convertor) is bad, as well as the catalytic converter itself (which makes a rattling noise when you take your foot of the accelerator and the motor returns to idle speed)

The fuel level in the tank was low (fuel reserve light was meanwhile on), so the first thing I did was fill the tank up almost completely. Another 50km was driven, then I reset all DTC's. No errors re-appeared. I meanwhile drove another 10km and still no errors.

Based upon what I could find on VCDS / VAG-COM: uitleg - tips - trics I understand that the 2 values that I can see in [Module-01], [Measuring Block-08], [Group 032] must be between +10% and -10% (or better even +5% and -5%) and they should certainly not exceed 25%. The values look to be called 'additive trim' and 'multiplicative trim'

Checking these values with VCDS I read :

- at idle motor speed (704 RPM) : additive trim (value 1 ) = 37,50% , multiplicative trim (value 2 ) = 0,0%
- at higher RPM's : additive trim (value 1 ) = 0,0% , multiplicative trim (value 2 ) = 0,0%

Not looking good... As 37,50% is far too high, and the 2nd value always remains 0,0%

I changed the 1st oxygen sensor with another one (not a new one - I stripped it from an identical AZQ motor from a crashed car I bought for spare parts - no idea what the state of the sensor is as I am at the moment not lucky to get that motor started). With this other oxygen sensor I am reading :

- at idle motor speed (704 RPM) : additive trim (value 1 ) = 3,9% , multiplicative trim (value 2 ) = 0,0%
- at 2912 RPM : additive trim (value 1 ) = 0,0% , multiplicative trim (value 2 ) = 7,0%
- at 4800 RPM : additive trim (value 1 ) = 0,0% , multiplicative trim (value 2 ) = 7,0%

This looks much better (values are within +/- 10% , the range mentioned on the gerritspeek site) and my old sensor before the catalytic convertor looks indeed to be bad, as nothing else was changed. But no idea if meanwhile my lambda value at the end of the exhaust pipe is within range now and ok to pass the technical control, hence my question of that value can be read out through VCDS