Help please -engine warning light [exhaust emissions value]

[Mad Professor]

I wonder if anyone could me -a bit worried actually .....
When i started her up tonight the Exhaust emissions warning light came on and wont go off -aaargh
It says in manual :warning light comes on when exhaust emission values have deteriorated -have the vehicle checked asap
Sounds kind of serious -what does this actually mean -is it safe to drive ?
Do i need to take it to BMW dealer to get this diagnosed -what could it be ?
Car seems to be running ok as far as i can tell but didn't want to drive it any distance
Thanks

 

[Scooba_Steve]

Could literally be any number of reasons.

If I were you I'd look on ebay and buy a BMW specific cable and software too - should cost no more than £30 and you'll be able to read your own faults. A fault read usually costs £60+ each time at dealer/indy so it will pay for itself twice, instantly!

My money is on a lambda sensor - I'd say this is most common. But you really need to have the code read, some are safe to drive on, others not. Lay it up if you can.

 

[srhutch]

Probably an O2 sensor, but you need to diag it yo know for sure.

 

[Mad Professor]

Ok I'll take it in to the BMW dealer and fingers crossed it's the O2 sensor and not a cracked manifold
Might ask the local BMW indie if he has the code reader ,presume a code reader at the Indie is same as one at BMW ,is that the case

 

[Mad Professor]

So is replacing an O2 sensor a big or time consuming job ,are we talking circa 500 squid at a dealer

 

[Scooba_Steve]

Dealer/Indy will have a reader but they won't sell you one. I got a BM Cables one - if you can wait buy one and don't get someone to do it for you. Even with next day delivery it will be cheaper.

Pre cat O2 sensors are easy DIY and only about £100 for genuine Bosch - £150 or so for BMW parts. At least £250 to replace a pre-cat, more for the post but these are less likely to fail.

That's assuming it is an O2 sensor, without having the fault read it could be anything.

 

[Mad Professor]

Thanks for the advice
Im not technical wrt cars so I'll have to get it diagnosed and repaired
I'll see what the indie says in the first instance when he puts it thru the diagnostic

 

[Stratts]

First check is an air leak, rather than the O2 sensor. Check the hoses from the MAF to the throttle, including the vacuum bits that connect to the brake servo etc. any tiny holes anywhere will cause the emission light to come on after a period of time.

A decent diagnostic read would highlight the issues better, but a fault with a n O2 sensor can sometimes be the symptom rather than the cause. Do the cheap and easy things first is my advice.

 

[Mad Professor]

Ok thanks for the heads up ,will mention that fur sure to the Indie when I take it in to check for leaks

 

[Mad Professor]

Grasping at straws but could it be due to dodgy fuel , I've only been using tesco 99 and been running fine on that until now

 

[srhutch]

It could be and it might clear after three to four ignition cycles. Fault code reader is what you need though.

 

[Georgio]

Grasping at straws but could it be due to dodgy fuel , I've only been using tesco 99 and been running fine on that until now

First off, don't panic; it's not a light telling you the engine is about to blow, it's a heads-up that's all.

Secondly it's 99% the fuel especially if you've just filled up with super-market special; I get the light virtually every time I have to use Sainsbury's fuel.
You have two choices, either take the car to a garage where they'll read the fault, cancel it and charge you, or buy a code reader off E-Bay for £30 and read/cancel the codes yourself.

Bear in mind that 'some' garages will involve lots of teeth sucking and talk of replacing both O2 sensors, closely followed by replacing the manifold etc, etc.
Look on any garage talk especially main dealers with extreme skepticism as they are skilled at emptying the wallets of the unwary... :roll:

 

[Stratts]

It's 99.999999% nothing to do with the fuel. The light is an emissions warning light, nothing more and is telling you the exhaust readings are above tolerance. Usually this is caused by the air/fuel mixture being off owing to an air leak, but it could just be a dodgy sensor.

The supermarket fuel is fine, no different to anything else. Bit of a waste to buy the 99 stuff but that's your choice.

 

[Georgio]

Well, that's the beauty of forums you always get different points of view, but I'd bet that when you get the code read it's a mis-match between the two O2 sensors; one is infront of the cat the other behind and the 'system' is expecting the post-cat one to be reading different than the post-cat one. Once this difference becomes out of tolerance a certain amount of times, bing, on comes the light....

 

[Mad Professor]

OK so took into my local BMW indie this am who are highly recommended and it's def the Lambda sensor not the O2 sensor which is fine - they have ordered up a new sensor from BMW parts -wont be here till Monday heyho -they have quoted me 400 squid with labour and VAT -sounds kind of reasonable -was expecting a much bigger bill ?

 

[Scooba_Steve]

Lambda/O2 sensor are usually taken to mean the same thing. If they are charging that for a pre-cat job then it's pretty steep - especially for an Indy.
Post cat, maybe not as unreasonable but these fail much less frequently.

For my pre-cat sensor I was quoted £250 from an Indy, £150 for the sensor and the rest labour.
I got a genuine Bosch sensor for £80, socket for £5 and lost 2 hours of my weekend

 

[Mad Professor]

Def said not O2 sensor

 

[Scooba_Steve]

If it's a sensor and it's plugged into the exhaust manifold pre- or post- cat then Lambda/O2 sensor they are essentially the same thing.

 

[Mad Professor]

ok fair enough -ill check with them tomorrow to clarify

 

[Scooba_Steve]

It's up to you what you do with it pal. If you're not handy then you'll always have to pay for these jobs. If you don't mind getting mucky and having a go then you can save a fair bit.
If it's a pre-cat sensor then I'd go DIY - post-cat probably not. Definitely get some detail on what needs doing and shop around.