Diagnostic (OBD) scan - What are they and why do I need one?

[Boostist]

This is becoming a very recurrent theme with forum posters so I have posted this to save the information being repeated over and over!

What should I do if my BMW has a fault light on the dash board that will not go off?

If you cant rectify the problem then a diagnostic scan is the answer

The engine light is back on and I only just had the car serviced?!

An OBD2 scan (or OBD 1 for pre 95 cars) is needed to read the codes properly.

My car has running problems and I just cant work out what it could be?? what should I do?

Get a diagnostic scan done by a competent local garage. Most will have the equipment to scan the vast majority of BMWs. Estimated cost should be between £25-£40~ depending on location and other factors. Get a printout (if possible) or handwritten list of the exact fault codes the ECU gave and then post them up on here.
It makes helping you out remotely a lot easier...

I dont know....is it worth it to get one of these OBD diagnostic scans done?? My car only runs badly internittently?!

YES, it is! The ECU stores fault codes as various components on the car report them during runtime.
So even if your fault is intermittent, there is a good chance that the ECU will have logged an error code during the fault period and this can save a lot of legwork and £££££.


In summary, newer BMWs have even more sensors and electronic reporting systems...so there is an even greater likelihood of a fault being reported.
With slightly older cars...it is still a BMW and as such is clever by nature! The fault codes can really be a great signpost to fixing any problems that are present on your car.

Examples//
A faulty ABS sensor that gives you an ABS warning light on your dash will report itself to the ECU, with many models actually telling the computer which sensor (which wheel) is at fault.

Your car is drinking (stupidly expensive) fuel like there is no tomorrow. Your pretty sure it never used to be this bad!!
What could it be?

There is a good chance that the Lambda sensor(s) (commonly known as the O2 sensor(s) ) could be at fault.
This will be logged in the ECU as a fault and will confirm if that is the problem.

This list will be added to as I have time!

[RYM]

Great sticky thread Boostist.

[Ronnie]

Good post Boostist

And before anybody asks OBD stands for On Board Diagnostics