Hi guys,

My ecu is throwing up a fault code for the O2 sensor. Im just wondering if the process for replacing the sensor is difficult? or if anyone is familiar with the process, whats involved?

Are the replacement sensors expensive?

Presumably this will affect my MPG is the sensor is not working, correct?#

Thanks guys,

2012

p.s. 2001 1.4 MPI Fabia

As the above fault has come up, I would like to know what the O2 sensor does, measures etc.

The O2 (Oxygen or lambda probe) sensor meaures the amount of Oxygen present in the exhaust gasses. Ideally the engine should run on 14.7 parts air to 1 part fuel, this is the optimum value. This air fuel ratio (AFR) of 14.7:1 is known as the stoichometric value and is denoted as Lambda = 1. This O2 information is sent to the engine ECU, which adjusts the fuelling to keep it at 14.7:1.

When the car emissions are measured at the MOT test, there will be a Lambda value, this should be ideally 1. If Lambda is less than 1, there is too much fuel/not enough air (rich), if it is more than 1 there is too much air/not enough fuel (weak), or a leak in the exhaust system

On the 1.4 MPi there are 2 O2 sensors. One before the catalyst (this is usually a 5 wire one) and a 4 wire one after the catalyst. The second probe monitors what the catalyst is doing.

Replacement sensors are around £100 and replacing them involves disconnecting the electrical plugs and unscrewing them from the exhaust, though there are associated problems with tight/inaccessible probes and getting your fingers burnt.

The fault code should specify which probe is at fault, in Skoda speak B1 S1 is the first probe (bank 1 probe 1) and B1 S2 the second probe (bank 1 probe 2). The probes have integral heaters, to get them up to working temperature, these can go wrong.

This air to fuel ratio, is this for petrol engines or deisels or both?

my car also show up the engine light due to oxygen sensor problem.

Where to locate this sensor?

my car also show up the engine light due to oxygen sensor problem. Where to locate this sensor?

They are fitted into the exhaust pipe, if two probes, one will be before the cat (control probe) bank 1 sensor 1 and one fitted after the cat (monitor probe) bank 1 sensor 2. You really do need to get the actual fault code(s) before just grabbing a new probe. There is a cheap one less than £40 from Gendan www.gendan.co.uk get the VAG one. After that search the internet for a full VAG fault code listing as the lists supplied with that tool is a bit short! Finding a full VAG fault code listing on-line is easy though. Remember it is quite rare, but a broken wire and/or a blown fuse can give you oxygen probe problems - as can dirty connector pins - but normally it will be a faulty probe.

This air to fuel ratio, is this for petrol engines or deisels or both?

Petrol only.

An engine will sometimes run a certain amount either side of stoichometric- a little richer at full throttle, weaker when cruising, but it won't vary far either side.

Diesels run with excess air most of the time, except at full power.

my car also show up the engine light due to oxygen sensor problem.

Where to locate this sensor?

Somewhere on the exhaust or exhaust downpipe. It depends on your car, and as Fordfan has said, there's often 2.