I have a 2001 1.4 16v Polo variant (estate) , unfortunately it just failed the MOT on emissions.

The garage was pretty useless and basically said they couldn't help me!

From what i can tell, the emissions test show it is running rich in petrol.

It failed on the FAST idle test with

CO = FAIL ( 1.158%)

Lambda = FAIL ( 0.965)

I have a Vag com and read the codes.

2 Faults Found:

17584 - Bank1: O2 (Lambda) Correction Behind Catalyst

P1176 - 35-00 - Control Limit Reached

16520 - Oxygen (Lambda) Sensor B1 S2

P0136 - 35-10 - Malfunction in Circuit - Intermittent

Readiness: 0000 0000

So from this it looks like i have 2 sensors? And it's the lambda After the cat that is iffy?

I thought that sensor is really more for saying when the cat is faulty though and shouldn't affect air/petrol mix?

I'd great appreciate any advice!

cheers

I'm no guru on this but looks like the one in front of the cat is intermittent faulty,controlling the mixture making it rich and the one behind the cat is OK and saying it's too rich?

John

Thanks for the reply.

I haven't managed to get under the car yet to see where the 2nd sensor is.

I found the first one, but there doesn't seem to be any error codes for that one.

First sensor is right at the front of the engine , just where the exhaust manifold starts . Poking through the hot air shield. That's definitely B1S1 as when I unplugged it, vag com said it was open circuit.

I've cleared the faults for the minute and going to try some redex and go for a blast and see what happens.

My 1.4 16V failed MOT on emissions, changed the lambda sensor (wired in a univesal one from eBay) and it then passed.

Just a little warning: Sensors, other than genuine VW ones, CAN be unreliable. G2racer obviously got a good one.

Regards.

Thanks for the replies guys.

I had a chat with another mechanic friend of mine and he confirmed that the post-cat lambda can affect emissions as well.

I've ordered a bosch one from ECP which will hopefully arrive tomorrow and i'll try and fix it! Probably going to be rusted on big time!

Will report back how i get one.

cheers

Now is the time to get under and give it some WD40 and let it penetrate till you're going to do the job...

John

Just had a look underneath.....

Found the sensor, in a tricky spot poking out the back of the top of the catalyser.

Just ordered a lambda wrench off amazon that i hope will squeeze in place!

The cable from it seems to run a long way under the car and back up to some place under the bonnet that i haven't found yet!

Sounds like cat and rear sensor change the sensor then try again if it fails on the co again it needs a catylst

Right, well I had the car running tiptop Smooth and no error codes, so I put off fitting a new second sensor.

Now typically the evening before the retest, it's come up with intermittent s2 and thrown the idling off a little.

Does anyone know where the 2nd sensor plugs in? I can see the cable running along the bottom of the car, then it disappears up into the dark depths of the engine bay and I have no idea where too!

The new sensor only comes with bare wires so I have to wire it on, hard to do without unplugging it!

ITS PASSED! :)

I didn't get round to fitting a new sensor but i found where Bank 1 Sensor 2 plugs in. It's just behind the engine, half way down near the rear-left corner.

I cleaned the contacts with IPA cleaner. It could still be intermittant though. will keep checking.

Also for good measure, stuck in a bottle of Cataclean, which is said to clean O2 sensors and catalysers.

I also put in some Milllers ECO max .

The results are an easy pass, with bizarely a negative value in one of them! The guy at the garage was eager to ask how i made it pass!

BEFORE:

AFTER:

I used that "Cataclean" and it certainly improved my MPG and the last MOT the emissions were well below the limits