2 Faults Found:

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1

P1196 - 35-10 - Electrical Malfunction - Intermittent

17589 - Linear O2 Sensor; Reference Voltage

P1181 - 35-10 - Open Circuit - Intermittent

I get the above although the car appears to run OK. I gather the 1.4 16v has a pre and post cat lambda? Would be good if someone can point me in the direction of the right lambda to replace.

Wondering if this is a replacement for it too.

http://www.ebay.co.uk/itm/121110265929?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I believe that is the front sensor AKA wideband lambda probe, that's the important pre-cat probe.

Not being familar with the manifold/downpipe layout in this engine, will the sensor be accessible from the front of the engine, i.e with the bonnet up, or is it an underneath job?

I've replaced that sensor on a BBY engine, and it was easier to remove the heat shield, but ultimately, I needed to attack it from below with an open ended spanner as there was not enough clearance to get a specialist socket in. For what it is worth, I'd walk away from using a second hand Lambda sensor, get a VAG one or equivalent NTK (it is NTK that VAG fit at factory) - I found that when I needed to replace the one on my wife's Polo, it was roughly the same price to buy locally from a VAG dealer than to get posted out an NTK one from an on-line vendor. Mind you, I don't know what you use that car for, but my wife's car needs to get up and go reliability once I've left for work so that she can get to work - so messing about with a cheapy was never an option.

To be honest, I am a diesel head and I don't know what the lambda sensor even does.

The car appears to start and run fine at the moment, but obviously I am not driving it on the road, so I don't know if the car is using more fuel than usual, etc.

B1 s1 is the front one in the exhaust manifold, it is possible to pass an emissions test without it working especially if it's open circuit, sometimes you won't even get an engine management light on either. so if you are selling the car on just ignore it.

There is no CEL, no. This is why I was surprised it came up on VCDS

Yeh one of my audi's is exactly the same, if it wasn't such a pig to get to I would have changed it stuck up there above the propshaft..

the way it normally works is the first probe is what generally called a regulating probe, it adjusts the fuel trim so the correct air fuel ratio is maintained by measuring the exhaust gas content, then the secondary probe after the catalyst is a check probe to verify the catalytic convertor is working at maximum efficiency.

if one of the probes fails or is unplugged it can operate soley on either one with with limited operating strategy ( kind of like limp mode)

normally on late vehicles like this the front probe is a wideband type which returns a 0-5v analogue voltage to the ecu, this voltage is directly proportionate to the air fuel ratio and has the advantage that the air fuel relationship can be mapped, so say for example it could be programmed to deliberately run lean at cruise speeds, or run rich at wot ( wide open throttle)

the post cat narrow band operates in a different way, it acts like a weak battery, it produces approx 0.3 volts when the engine is lean, approx 0.7 volts when running rich and this is set to a predetermined stoichiometric air fuel ratio of circa 14.7:1

the way the closed loop fueling operates is the ecu constantly cycles rich/lean approx every 2 seconds, the feedback from the sensors tells the ecu that the engine is running close to ideal fueling, so it always hovers over the correct air fuel ratio

you should be able to see the output voltages of both probes in the measuring blocks using vcds, it's group 1 iirc, you will see the second prob switching between the to voltages roughly every 2 seconds, you front probe is broke so you won't see owt on that

it's not quite as simplistic as I make out, but I dont want to confuse anybody with the inner workings of closed loop fueling, so in summary, yes you will have slightly reduced efficiency but I'd wager you'll never notice the difference. Hope this make sense Jason?

Thanks. I will have a flick through group 1 measuring blocks at some point this evening.

Actually it might be group 31 on that type of ecu, I must confess I can't remember.

Tom has it about right but you can get away with the post-cat lambda failing since it doesn't affect fuel trim, it just throws the CEL to indicate that the cat or the probe itself has failed in some way. It's quite common to blank off the post-cat sensor with a cap and some tape and zip tie it up out of the way somewhere when you run a decat exhaust so that the CEL doen't come on.

Edited 7 June, 201313 yr by sepulchrave

Mine flashed that up once, just cleaned up the connector with some electrical cleaner and it fixed it.

When you open the bonnet the Exhaust manifold is right at the front with a PITA metal cowling. get that off and theres the sensor. alternatively the connector is positioned not far from it but for memory you need to get under the front of the car.