Octavia 1.4TSI 140ps emissions failure at mot

[KeithJR]

The local garage I just took my car to for mot tell me that its failed Fast Idle Test CO reading way over the top @46k miles, also the Lamda sensor not showing any output. As this would normally show up as a fault (none showing on dash), they asked me has the software been tweaked to mask the lamda sensor fault. As far as I know the answer to that is no.

 

The history behind this is that my previous mot at another garage initially showed the same fault, but I ended up with a pass and all emission shown ok. Dont know how they got from fail to pass. It all sounds dodgy to the suspicious mind.

 

My question is, is it possible to mask out a lamda fault in this way? The garage where the car is now are now offering to reflash the software to std spec and fit a new lamda sensor hoping to get a pass, but say that the cat. might be in trouble due to running around rich

 

The garage seem honest enough. Just wondered if what they are saying sounds reasonable?

 

Worried🥺

[ChoonDoode]

I can't imagine you'd be able to mask a fault with a lambda sensor. The ECU's are too clever. By all means, you can wipe the fault off the log, but if indeed there is still a fault with it, it's going to keep coming back. Do you have notifications on the dash or the car info page on the infotainment?

 

Without having a scan of it with VCDS or an equivalent, it would be hard to give a thorough diagnosis, which is what the garage sounds like they're looking to do, but I can't see why they'd be reflashing software unless they know that's the problem. I assume this isn't a main dealer who's telling you this?

 

It would be a case of checking for any errors on your car and should they find any, fixing the root cause of those. Anyone can swap parts til the cows come home with the hope of fixing the problem.

 

With emissions problems, it does sound like the car is being incorrectly fueled. So MAF and lambda sensors are main places to look at. So best case scenario is a new MAF lambda sensor and you're sorted. You may have blackened spark plugs caused by the unburnt fuel, so at some point they may need changing. Also, depending how long this problem has been going on, would depend on whether it's been making your cat work overtime. That's a worst case needing that looking at.

 

The other questions would be what's the service history of the car like / how long have you had it? Also, how does the car drive day to day, is it sluggish to get a giddy on?

[KeithJR]

Nothing showing on the dash before it went in, thats all I can say for sure. Its a small independent garage looking at it, now waiting for new lambda sensor. Ive had the car 4 years, full service history, drives like a dream, very responsive to throttle. Cam belt done last year and before that had an issue with the waste gate actuator pivot seized. Found info on here about that and got it replaced /  greased up. Will know more tomorrow when the new lambda sensor is fitted. New plugs fitted as part of the service which was due as well.

[classic]

1 hour ago, KeithJR said:

Nothing showing on the dash before it went in, thats all I can say for sure. Its a small independent garage looking at it, now waiting for new lambda sensor. Ive had the car 4 years, full service history, drives like a dream, very responsive to throttle. Cam belt done last year and before that had an issue with the waste gate actuator pivot seized. Found info on here about that and got it replaced /  greased up. Will know more tomorrow when the new lambda sensor is fitted. New plugs fitted as part of the service which was due as well.

 

I’m fairly sure that it’s possible to have a faulty lambda sensor and not get a warning light. If I remember correctly the sensor produces more voltage as the fue/air ratio gets richer, so low or no voltage would be seen by the ecu as a weak mixture and it would increase fuel and keep trying to overcome that. 
If they are saying there’s  no output from the lambda probe, my interpretation would be that, it, or it’s wiring, are probably faulty. There are at least 2 lambda sensors, one before the cat and one after it, the ecu uses the readings from both to detect the efficiency of the catalytic converter and if it sees little or no difference in oxygen levels that would put the warning light on to signal a fault.

 Having said that there’s many other possibilities, the catalytic converter needs to be well up to operating temp or it could even be a simple air leak somewhere or slight misfire.

[KeithJR]

Got the car back, all fixed. 😃

After the new Lambda sensor was fitted, the emissions were still failing. Then some software updates were applied and emissions were all good. So maybe I have been driving around since the last mot with problems that were masked. Thankfully the catalytic converter was not affected by all this.

Edited 5 June, 2020 by KeithJR
clarity

[Guest]

3 minutes ago, KeithJR said:

Then some software updates were applied and emissions were all good.

 

It's the VAG way