My 2006 Fabia 1.2 has developed an intermittent check engine light, and i have plugged a diagnostics reader in which reads code PO171 System to lean bank 1. The CEL light seems to come on an off at random intervals, and when it is not on there is a 'pending' code showing on my diagnostics reader.

I have not long owned the car and i know the downstream lambda sensor was replaced when i bought it, wondering if the upstream one needs changing also. The car seems to drive ok regardless of whether the light is on or not. 

Does anyone have any ideas on what the issue could be?

I think its the 'AZQ' engine 3 cylinder 1.2 64hp, done 96,000 miles.

BME code engine in 2006, I reckon.

Check the brake servo vacuum pipe, especially the joins between hard plastic pipe and other bits.

Yeah your probably right i just went off what it said on wikipedia. 

Will check that line tomorrow, any reason why that causes this error code?

If its any link the brake pedal seems to have a really long travel but could just be a characteristic of the car

update:

nothing apparently wrong with the brake vacuum line

used a bottle of redex in the fuel tank and reset the light using OBD reader. so far it hasnt come back on so maybe it was an issue with dirty injectors/blocked fuel lines