Decision time

[mzarifkar]

Mechanic says i need a new MAF and O2 sensor, based on codes. I suspect the fault of these has led to a bad cat as well, but that is a different story.

Prior to spending money on these, are there any relays perhaps i should check before settling on faulty parts?

[BMWDriver]

O2 sensor should be tested before replacing. The part is expensive enough that it warrants it.

[h2oyo]

O2 sensor should be tested before replacing. The part is expensive enough that it warrants it.

+1 on the testing, I would test both parts before replacing. Its not difficult with a good fluke and the Bentley for direction.

[yaofeng]

What's the symptom? Check out the following link for my saga getting over the NJ emissions hurdle. You can test the O2 sensor reasonably easy with a fluke multimeter.

http://www.bimmerboard.com/forums/posts/628805/

[mzarifkar]

poor power, which resolves after unplugging MAF, which likely makes it run rich, while likely spoiled the O2 sensor and Cat

[Ross]

Ditto the MAF which costs plenty. A malfunctioning MAF will cause an incorrect mixture that will set the O2 sensor code.
A code doesn't indicate need for component replacement, only that a sensor has detected a value outside of a predetermined normal range. This is a STARTING POINT for "diagnosis", a term lost on so many of today's mechanics.

[Ferret]

Dont forget these codes could be being thrown because of an air leak... are you *sure* everything's buttoned up correctly and there's no leaks/cracks in your hoses?

[mzarifkar]

I will double check all hoses for possible leaks and perform the excellent MAF test Shogun wrote about. I will check the O2 sensor relay as well. I already have a O2 sensor, any experience with the less than $300 MAFs?