Engine Management Light on - Info on o2 sensor please

[devan]

This morning when i left work the engine management light came on, on my 2002 S3.

I had just finished a night shift so didnt have time to investigate so i drove it home approx 2 miles and went to bed, the car drives normally too btw.

Then when I woke up this afternoon i went back out to see if the lamp was still on, and it was. So i decided to drive to the local Tesco's carpark and call the RAC as if ive just broken down. Lucily the RAC man was actually in Tesco when i called them, so he was with me within 2 mins. He scanned the car using his laptop, and it came up with fault code: P315, which he says is the o2/lambda sensor. The fault code on the laptop explained it was to do with the heating element/wiring of the sensor. He then displayed an instantaneous graph showing the voltage coming from the sensor, with respect to when he pressed the accelerator, and it was not changing. He cleared the light, and told me to replace the lambda sensor.

I have been doing research, and I presume I need the pre-cat sensor, but understand its a pita to replace yourself?
Does anybody have any info on this fault, and/or help with replacing the sensor please?

Cheers,
Ash.

 

[Nilz]

Hey Ash

Did it say which sensor it was as there are 2 on the S3, there is one at the back of the engine bay (bank 1) and another one just about under the drivers seat (bank 2) - (under the car obviously).

The one at the back of the engine bay is a bit of a pita to get to and replace, however the one on the bottom of the car aint too bad, as long as you can get under it, decent jack/ramp.

 

[devan]

Hi Nilz,

It probably did say on the laptop which one it was, but i didnt think to ask because i only thought they had one , however bank 1 rings a bell. Plus ive just got it on the jack and checked out bank 2, including the junction box where it plugs into the wiring loom. I didnt take the sensor out because it was tight as hell and didnt want to risk it. But it all looked to be ok. Obviously the sensor could be faulty, so im not sure what to do now. I guess i really need vag-com to scan it again.

I also had a look for the bank 1 sensor, but couldnt see it, do you know where abouts it is, im guessing its right near the exhaust manifold because i couldnt see it going into the cats when it was jacked up.

Does anybody have a vag-com they wouldnt mind sticking on my car to check which sensor it is please? Im in S****horpe, North Lincs.

Cheers,
Ash.

 

[devan]

Or does anybody recommend one of these for a fraction of the cost of a vag-com kit?

VW VAG COM Diagnostic Fault Code Reader CAN OBD2 | eBay

 

[Nilz]

bank 1 is literally at the back of the engine bay when you open the bonnet, it is hidden away though!!

You can get a cheapo vagcom cable (one of the blue ones) and then install vcds lite off the ross tech website, its ok and basic, you cannot make any changes, bu tits good for fault code reading.

that will give you a defo description of what the issue is.

The one at the bottom of the car is sealed quite well and the main fault with this is that it does actually die, theres not much else that can go wrong with it.

 

[devan]

Ok cheers Nilz,

Think im going to order the full vcds in the new year, in the mean time im going to check the resistance across the lambda sensor heating elements, and see if i can see any other obvious fault until the vcds arrives.

Cheers,
Ash.

 

[Speedy Steve]

Oh how i remember the fun we had changing your top Lambda sensor Nilz. I actually found the top one easier to change with a proper lambda socket that the bottom one. Infact i never changed my bottom one i got bill to do it when he fitted my down pipe lol

 

[devan]

Well it looks like its also my pre-cat one which will need changing

Just checked the resistance across both lambdas and pre-cat is open circuit, and post cat is 10.5ohms.

 

[devan]

Its fixed!

OEM pre-cat lambda picked up and fitted today from a local vw/audi private spares dealer, and if anybody wants it for future reference, Kwikfit will charge £35 to plug the car into their reader and check, which is what i did in the end because I wanted proof it was definately the pre-cat one, and I couldnt be bothered to wait for a £20 OBDII reader from the Internet. Kwikfit also cleared the fault light for me for free after i had changed the sensor, so pretty pleased with that.

And surprisingly the lambda came out really easily, i just bought an NGK lambda socket for £3 from a local car shop, and used various ratchet attachments to get it out and new one back in. Oh and the local VW dealer wanted to charge £60 just to diagnose the faults!!!!

 

[Nilz]

Nice one, glad you got it sorted.

 

[Welly]

Oh how i remember the fun we had changing your top Lambda sensor Nilz. I actually found the top one easier to change with a proper lambda socket that the bottom one. Infact i never changed my bottom one i got bill to do it when he fitted my down pipe lol

You can just about do it with an adjustable spanner. It's tight mind.

 

[Nilz]

I think we did end up using an adjustable spanner....well I say we...I mean Steve, whilst I stood about freezing my bollards off!!