Fault Code 17559,please help!

Hi!

My mom has a Skoda Fabia Combi 1,4 I 16 V .

The problem is that the engine management light keeps popping on and staying on without anyone finding out the exact fault.The cars performance is *NOT* affected in anyway.She`s been to the car dealer seven times with this fault.Last time they change one of the lambda probes,to days later the engine management light popped up again.

A second car dealer she used some days ago told her:

Fault code 17559

Bank1 ,Sector 1 Mixture adaption (min limit exeded.Mixture to lean).

The car emission test that was done ,showed nothing abnormal.

A Volt test of both lambda probes showed that there were very little volt variations in the first lambda probe ,about 750 mV (located near the exhaust manifold).The second lambda probe (located after the catalytic converter) had more "normal" volt variation from 150 mV to 750 mV.The lowest volt occurred after the catalytic converter had reached a temperature of 450