My 2003 Octavia failed its MOT on the emissions a couple of days ago, and I am trying to diagnose why. The results were:

Fast Idle tests

CO (Limit 0.3%): 1.05% (1st Test) 1.77% (2nd Test)

HC (Limit 200ppm): 247 (1st Test) 233 (2nd test)

Lambda: 0.96 (1st Test) 0.98 (2nd Test)

Natural Idle test

CO: 3.83%

Suspicion has fallen on the Oxygen sensors. I have attempted to check the output from the two sensors, and have used both a Snap-on Solus gadget and Vag-Com. I have attached a screenshot of the readings from measuring block 31 which i believe is showing the voltages from the sensors, and one does not appear to be switching at all, and the other only sporadically when coming off the power and breaking. Red line is the RPM and the blue and orange are the sensors. Its a 1.6 engine, code BFQ.

Unfortunatly due to lack of ramps/axle stands I have not been able to get at the sensors directly to check the voltage at the connectors. From this info am I looking at the right things, or am I barking up the wrong tree completly? Last year I did have the MAF sensor replaced as it was aparently faulty. Could this be related to that, although it passed the MOT last year without problem.

Also, any reccomendadions for a place to take the car to get it sorted around the Northampton area?

Thanks

Jon

take it to Unit 18

Apologies, I appear to have acidentaly posted in the wrong forum!

Mods: please feel free to delete this post, I shall posta again in the propepr place!

3 things

Was the engine hot when they tested it, or did they mot it 1st then do emmissions?

Unless it was up to temp they may have conned you into getting work done.

Air Filter, these can cause this if too dirty.

Fuel Injector cleaner in half a tank, a bad spray pattern will also mess with the results.

So get a new air filter 1st, then put some cleaner in the tank, then go for a 20 mile drive @ 70mph in 3rd and 4th gear, you want to get some cleaner through it @ 4k rpm to have a chance of cleaning them, them boot test it, this is just stand one foot in the car and one out and rev it to 4000 rpm and hold it for 15 seconds, you may have an initial burst of black/grey smoke, this is normal, the acid test is if it stops soon after while reving it, and finally make sure you come straight off a motorway with a hot engine and get that probe in it's ass asap, hth.

Topics merged into appropriate section and duplicate & non relevant posts deleted.

It certainly looks like its got a problem, my 19 year old carburettored Ford produced better results. Surely there must be a fault code stored with results like that. Sound advice given in post #3 above.

What were the O2 readings?

Hi

Thanks for the responses so far.

The engine should have been up to temp as it went for its MOT after a 30min drive home from work where I deliberatly made sure it got nice and warm. The air filter looks fine, though for the sake of a few quid i may as well change that.

I checked for fault codes, and all that was present was one relating to the MAF sensor giving an implaudible reading, though that is from quite a while ago, and the engin light has not been on for a good few months. Think I may give Unit 18 a call on monday as they are quite close to where I am.

Not too sure what the actual o2 readings where, What measuring block would I need to look in to see these?

When my MAF failed I didn't get a CEL but had the implausible signal faults.