Right. After a couple of wheel bearings, and some brakes, and some springs, my Octavia is almost ready for MoT. Only thing is, it's failing now on emissions.

The EML is on, with the code for the SAI solenoid - firstly, is this going to be affecting emissions for the MoT test, and secondly is it easy (and expensive) to fix or replace?

There's also a leak around the backbox that isn't helping matters... where's the best place to get one? Even if I have to cut the existing one-piece pipe to fit the new back box, that's not a problem.

What's an SAI solenoid?, what code is coming up? An exhaust leak will affect the lambda reading, what are the emissions readings? The exhausts as fitted at the factory are one piece, when replacing just the rear section the factory fitted exhaust should be marked at where to cut it. VWs Trade Parts Speciallists were advertising some budget rear box applications, I don't know if the VRS was listed amongst them.

SAI is the secondary air injection, a system that's there to reduce emissions from a cold start.

Wouldn't have thought a SAI fault would cause high emissions as it only operates to help warm the cat converter up on cold start. I'd have thought that you either have a faulty CTS or one of the Lambda sensors is failing.

What's an SAI solenoid?, what code is coming up? An exhaust leak will affect the lambda reading, what are the emissions readings? The exhausts as fitted at the factory are one piece, when replacing just the rear section the factory fitted exhaust should be marked at where to cut it. VWs Trade Parts Speciallists were advertising some budget rear box applications, I don't know if the VRS was listed amongst them.

vRS not listed sadly - had a good look through the book.

Wouldn't have thought a SAI fault would cause high emissions as it only operates to help warm the cat converter up on cold start. I'd have thought that you either have a faulty CTS or one of the Lambda sensors is failing.

CTS? Is there a way to diagnose further with VAGCOM or similar, rather than replacing parts willy nilly? I'll be looking at getting a back box first, then retrying the emissions test.

vRS not listed sadly - had a good look through the book.

CTS? Is there a way to diagnose further with VAGCOM or similar, rather than replacing parts willy nilly? I'll be looking at getting a back box first, then retrying the emissions test.

Coolant Temp Sensor. If you follow the rad top hose the CTS is under the smaller of the 2 engine covers, If you have the old black type it's very likely that it's faulty. If you have the later revised green CTS it's probably ok as they rarely fail.

Yes check for codes with Vagcom if you have it, but a faulty CTS doesn't always throw a code. Lambda sensor failure should throw a code though.

Edited 27 November, 201015 yr by pauldazzle

D'oh, CTS, of course. Should be OK - I got a new one six months back, since it was easier than changing the thermostat... which I then ended up changing anyway. Temp gauge on the dash is reading normal, if that points to the CTS being OK?

Cheers mate.

The CTS has 2 feeds, 1 goes to the gauge & the other to the ECU so a working gauge doesn't mean the CTS is ok. If you put a genuine VAG green CTS in then I doubt it's at fault.

You really need to get Vagcom diagnosis before you start throwing parts at it.