Hello all and thanks in advance for all your expertise!

 

So... My Fabia is a 56 reg, 1.4 litre petrol. Had it a year, no problems so far. It runs well and has always been reliable. 

 

Over the last couple of months I've noticed fuel efficiency going down from average 37 to 35, I was a bit worried but thought maybe I've become more of a racer girl?

 

It had a full service and MOT 2 weeks ago in a good garage I trust. But a day later the emissions light came on. I called the garage - they said bring it in, it's safe to drive and that they'll check if it's anything they've done. They had it one day, went through everything. They had the error reader which said:

 

16555 Fuel Trim Bank 1 System Too Lean P0171 Short With Power

 

They then reset the code, obviously all free of charge. The guy said the oxygen (lambda) sensor looked non-standard and showed me, he said it might be the issue. The light stayed off for 2 weeks... then came on again today :(

 

In the meanwhile the car runs really really nicely, very smooth. But fuel efficiency doesn't go about 35.5 even when I'm very gentle.

 

So, I have a few questions - 

 

What do people think might be the issues?

Would you recommend I go to main dealership and pay again for diagnostics etc, or stay with my garage?

Is it safe to drive, and if so for how long?

If it's the oxygen sensor, how much can I expect to pay roughly?

 

Many thanks, this is really stressing me out as I'm totally reliant on my car for a 60 miles per day commute to work!

Correction - it's a 1.2 litre engine not 1.4.

It's very likely to be a vacuum leak, possibly in the brake servo pipe, they're known to split.

 

That's really poor economy from a 1.2 on a longer commute, you may have the dreaded leaky valve seats, only a compression/leakdown test will confirm it, your regular garage can do it for you.

How many miles has the car covered to date? Do you have any service history that suggests that the fuel filter has ever been replaced?

 

Welcome to Briskoda .

Thank you, it's good to have some advice

 

The car only did about 45,000 miles. Fuel filter was replaced in the full service 2 weeks ago! As were the oil, air and pollen filter and the plugs...

 

Btw, the error code website wiki.ross-tech says

16555/P0171/000369 - Fuel Trim; Bank 1: System Too Lean Possible Causes

• Mass Air Flow Sensor (G70) defective
• Intake System Leak(s)

 

So nothing to do with lambda sensor...?

In that case, sepulchrave's suggestion of the brake servo vacuum leak is hot favourite, I think.

Cool, will ask my guy to have a look!

Final question: how long do you think it's safe to drive my car before taking it to a garage, if the fault is as suspected? Is it urgent?? I might only be able to sort it out next week, but obviously if this could cause serious damage to my engine or explode or something I'll see if I can take it in sooner...

Relax, nothing bad will happen, get it done at your leisure.

OK. So took car to the garage, the guy looked at the brake servo and valves and apparently these are all in order and there are no leaks. He suggested the MAP sensor might need replacing so he's looking into this, does it sound about right?

No. The MAP sensor almost never goes wrong, hundreds of people come on here all the time, their garage always changes the bloody MAP sensor and it never fixes the problem. It just means the garage is hopeless at diagnostics, most of them are I'm afraid..

Gahhh. Well it's done now though it probably won't make a difference :( what are we left with options wise if it's not brake servo pads or valves?

Brief update: MPG is up to 38.5 from 35ish so maybe it was the MAP sensor after all? Will wait to see if the dreaded light returns. Thank you all for your help and advice!

I don't know whether this is appropriate for Skoda petrol engines but on my diesel cars I quite often reset the ECU which always seems to bring a better performance and MPG - No doubt someone will either confirm or condemn.

If it is appropriate then do this.

With a warm engine, switch off ALL electrics, disconnect the battery for 30 minutes, then without touching any pedals or switches start up and leave to idle for 30 minutes and hopefully things may now have improved.

DB.