Car warning light oxygen or O2, sensor, lambda

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Has your yellow light has just come on the car dash?

If so then the sound of cash registers will be ringing in the ears of your dealer so pop down to the bank and fill a wheelbarrow with money OR follow this quick and dirty guide...

    * My yellow light is on = oh bugger, don’t worry read on...
    ** This guide is for people whos motor was running fine before for MANY trouble free miles and who got a yellow light after 30 to 40k miles on the same previously unchanged oxygen sensor if your motor was toublesome running in other areas before then get a code reader and assume this guide is NOT for you! and it wont help...
Ok so what is an o2 lambda oxygen sensor = it is a thing wot looks like a spark plug usually found on the outlet manifold of an exhaust system, it has 2 or 4 wires sticking out the top, (sometimes there are more than 1 , actual 2 in fact... follow the the pipe where the hot gas does go and they shalt be there because is their job is to electronically sniff your exhaust gasses and to tell the Engine Management Unit what’s going on so then the EMU can use less petrol, up to 25% less in fact...

 So....   How do I know its my o2 sensor wots broke? = because they wear out , if the rest of your car was running ok , then it ran lumpy, then the light came on and you aint changed the o2 sensor for 30 to 40k miles then it is about 90% certain that your sensor(s) is (are) shagged
So ... Will my car engine be damaged if I run on the yellow light? = probably not if its just the o2 sensor because in most cases the cars EMU will click to a default setting (some call this a "get you home setting" - yawn) in reality it just cant sniff the action at the exhaust to allow a 25% leaner mix on a hot and fast run , and a yellow light pops on ... , but don’t run your motor indefinitely like this as deposits of unburned fuel can build up and cause other problems, I ran my car for 1000 miles before sorting & had no problems whatsoever.

So ... How do I change the sensor? You Buy a special socket from eBay or the web (about £8) you then find the pdf version of the replacement NGK oxygen sensor book available on the web , find your car make model and year locate the part number and shop around (web motor factors etc) until you get the best price .... also cross check the connecting plug diagram illustrated in the book as your oxygen sensor may be used on other similar models or engines - this is VITAL if you have this issue go for the sensor with the CORRECTLY illustrated and EXACTLY MATCHING the diagrams CONNECTOR BLOCK, this is as well as matching the make model and year in the index - check twice ! because sometimes (as happened to me) the  02 sensors can be used on slightly different engine sizes... as happened with my Mitusbushi Carisma - the o2 sensor i needed was listed against a different engine size - SO CHECK YOUR CONNECTOR MATCHES THE PICTURE IN THE BOOK

Fitting the new sensor
do i need to say ignition off? car not running? thought not :0) so ...
Follow the o2 sensor wire until you find its connector block, look for the locking tab release, press it in to release, and pull the connector apart
Using you special socket tool , remove the old sensor (exactly like unscrewing a sparkplug)
Now screw in the new sensor until hand tight when you feel it gently bed into the threads turn the spanner  one quarter to one third of a full turn to get the right tightness (torque) in fact exactly sparkplug tight ! geeky types may notice the exact same type of compressible heat resistant washer found on Mr Sparkplug... like me :0~

Reconnect the wires by clicking the new connector block on
Now we have a new sensor fitted in BUT we have one more thing to do, ...
The error code in the memory of your cars electronics will keep the yellow light ON, so we need to clear that error code, the way we do this is to reset & reboot the system, this is done by, removing the battery connector +POSITIVE (red) so using a 10mil spanner (usually) pop off the battery connector and leave it

off for about 3 minutes, bear in mind that you may need to reset stuff like the security code in your radio also if you disconnect the battery,  then reconnect the battery, this works maybe 90% of the time HOWEVER although some systems MAY require you to clear the error code in another way. more on this below

Now start the engine, the engine should run smoothly and the light should be off if the light is still on but the car runs normal and your fuel economy returns to normal - i.e. is about 20% better then you may have to do 1 of 2 things

1 Go to the dealer and get them to clear the code (£60 PLUS VAT AND LIES, MAYBE £600 - sucks air in through teeth) OR

2 Buy a code reader off eBay (£30 to £80) and clear it yourself - sounds hard but its >>> NOT <<< imaginge connecting something a scart lead to a socket on your car and then scrolling down something like an old mobile phone menu a menu until you pop off the light using a menu option... well thats pretty much what you do... just make sure your car is ODB2 compatible & compliant (nearly 100% of cars after 2001) buy a compatible error reader , making sure it has the ability to also clear codes too, basically you plug it into the ODB2 connector (a scart looking socket, which by law is located within 2 feet of the driver) and then you read the memory of the ecu , then clear any error codes it found on a hand held unit - its easy the trick is making 100% sure your the box you buy will talk to your car. - check car spec - manufacturer info , owners clubs / web boards etc

          o IF the light is reset and turned off and then after 20 mins and comes back on again then you have either one of 3 things
                1 a faulty sensor (bad luck - cos that’s rare)
                2 the wrong sensor (most likeley)
                3 a fault with something else (possible,if you suspect this, then really now is the time you need to get a fault code reader, and get it to pinpoint the exact location of the fault , dont worry all good code readers will tell you that CODE 997986 corresponds to a bit of your car that needs or replacing or repairing ... last word of warning, you can get UNIVERSAL 02 SENSORS for about £20 - probably best NOT TO, as 4 wire sensors can contain a built in heating element , this can be different amperages so yes it will fit in the hole BUT the yellow light may be re triggered by this incompatibility also the wire colours are wrong and there will be no plug on it so you wuill have to butcher your old plug and connect the wires manually... all these things are a bad idea and will lead to failure and this guide is written for your personal success! SO BEST NOT TO GO UNIVERSAL! cos one size aint gonna fit all in this case - physically YES - electromechanically NOOOOOOO!

DON’T BOTHER also some cars have MORE than 1 sensor and sometimes they are further down the exhaust system
ANYWAY that is my guide is should be good for about 95% of cars and situations, the other 5% of you will find the fault if you get an ODBC reader and this may lead to a new .... oh I dont know ... err lets say air sensor ... you will change the bad bit and reset the ECU and bingo you will be very happy , some of you may not be so lucky and like my freind have to get his ECU remapped (reprogrammed) to stop soot blocking stuff up (Ford CMax) so always check for known yellow light issues first ,,, this guide was for a car working fine that went lumpy with a yellow light after 30 to 60k miles ... this is classic O2 issue.

Now lets look at what you might save
A dealer who likes to make lots of money out of your ignorance will fleece you of all of your money and public hair whilst tell you all sorts of crap which you have no way of proving or disproving they will say : blocked injectors, faulty engine management unit, faulty sensors, in the air intake, fuel system etc etc , they will ordinarily keep your car a few days and charge you a massive £600 to £1200 billing you for loads of false labour and a EMU or an EMU refurb they probably aint fitted and aint done. Also they will charge you £55 to £120 to read an error code (per read!) if you try to DIY via the dealer - so don’t bother, buy your own reader and code clearer. Also buy a factor sensor (NGK) cos if you buy their O2 sensor expect to pay up to £200+ oh yes £200 notes for something that costs spark plug money to make ....nice ...

using this guide
NGK replacement £80 to £140 maybe (total) if you fix it fist attempt plus £8 for a O2 spanner
or add £30 to £80 if you really have to buy that ODB2 code reader.

Your saving? well you will be saving that wheelbarrow full of money I was talking about earlier.
GOOD LUCK and may your fleece stay upon you, and not in the pockets of the naughty dealers or garages.