BMW 520 E39 Cat failure? - PB
A friend has a 97R 520 with 100k on the clock. Recently it lost power badly and won't rev above 4000rpm now. The dealer says it needs a new cat for the exhaust. Does anyone know if this is normal atthis age, and if the diagnosis sounds right? Also is this worth getting done at a BMW specialist? Anyone know a good one in Berkshire? Thanks,
BMW 520 E39 Cat failure? - Cyd
I would say not normal. I would expect that a car with this high(ish) mileage should have no cat problems. Short journeys and lots of unburnt fuel are cat killers. In the US cats must be warranted for 100k by law.

Car's not burning oil is it? 'course the cat could have suffered mechanical damage or a severe dowsing on our wet roads.

One presumes that the dealer has examined the car to reach this diagnosis, in which case there's little reason to doubt their word. I'd ask them to examine the car carefully to make sure there isn't some other underlying problem which has caused the cat failure. Since the car is quite young, I'd go for a OE replacement.

If the car has full BM dealer service history, I'd press for a contribution towards repair costs - the cat really should last a lot longer than this.
BMW 520 E39 Cat failure? - David R
I don't know if its the Cat or not, but if it is make sure your friend gets the genuine BMW part. My 318's Cat failed at about 100000 miles and to save money I got a Bosel Cat from Kwik Fit. It failed after 2 months and was replaced. This saga was repeated every 2 months for a year. As the end of the warranty period approached and the cat was stuffed again the Kwik Fit manager suggested I pay the difference between Bosel and BMW and get the genuine part. Needless to say this was the answer. I will be slow to stray from BMW parts again.

BMW 520 E39 Cat failure? - Dizzy {P}
I don't think a BMW E39 cat should fail after only five years. The one on my ten-year-old 525i E34 (118,000 miles) is the original and the MoT tester told me that it was very rare for BMW cats to fail and he couldn't remember the last one he came across.

On the other hand, my daughter's late-1996 Peugeot 106 needed a new cat after five years and 65,000 miles, and the replacement (non-Peugeot) lasted less than a year! This was replaced under warranty but we expect to be buying yet another before long.

I agree entirely about buying genuine BMW exhaust parts. The only part of mine that has needed replacement in ten years is the back box and the genuine part that I fitted is superbly made and will probably outlast the car. (I know that the system on the car was original because the factory-fit centre/rear assembly is all-in-one whereas the service replacements are separate items).
BMW 520 E39 Cat failure? - GGH
I recommend you have your Lamba oxygen sensor checked. My 320i sensor failed at 50,000 miles, I had it diagnosed by computer at a PTA motering centre. Symptons were nil or erratic tickover, hunting, and lack of power.Bosch replacement part cost approx. £65 from German and Swedish or £120 from BMW. Beware, if you fit it yourself, it is a pig to get at in situ on a 320i, I had to buy a special type and shape of spanner.
Also check for any split or air leak in the rubber bellows fitted to the air inlet side of the inlet manifold. Best of luck, GGH


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