BMW breather hose failure a.k.a. oil separator drainback hose   Leave a comment


We at Autobahn Performance Inc. have seen an abundance of drivability and check engine light problems for this breather hose failure. We changed three today. We usually keep 2 in inventory but will increase that number. The replacement part is inexpensive and fairly easy to replace although it is tough to see and even tougher to access. The symptom for this hose failure is usually a slightly rough idle, hesitation when accelerating at times, and rough running engine (misfires). The check engine light will usually be on with multiple codes set for misfires on some or all cylinders (codes p0301 – p0306) and random misfire (code p0300). There are usually a couple of fuel trim management codes set.
These are indicators that the fuel mixture is outside the normal controllable parameters. On a Mercedes this would almost automatically be an air mass sensor MAS or MAF sensor. We have seen lots of shops replace the MAF sensor, reset the fuel adaptation, and send this BMW customer down the road, only to have them return within a few days with the same codes set. Then the spark plugs usually get replaced — list price is currently $17.50 for each plug. The factory NGK 3199 plugs are supposed to last 100,000 miles although we recommend replacing them at 75,000 as most customers will notice an improvement in drivability and fuel mileage when done at 75,000 miles. Make sure to use the NGK plug as they seem to work and last better and longer than any other spark plug in these engines. This is opposite of what we have preached for years when we would only install BOSCH spark plugs. As a rule we try to install the same plug the vehicle left the factory with (except Bremi plugs — but that is a different story). The customer gets sent down the road again only to have the check engine light return within a few days and usually complain that the vehicle is just not running quite right. Hopefully by now the technician checks things thoroughly enough to discover the broken hose under the intake manifold. It is just barely visible with a small flashlight or a bend-a-light. The hose is easiest changed from beneath the vehicle, although it is not an easy job and brittle plastic components and other hoses must be carefully dealt with to gain access to the suspect hose. The new replacement hose may not look the same as the old one: the part has been updated, but even the updated part has been known to fail. The picture below shows one of the common high failure rate hoses on the top and its replacement on the bottom.  -> JASON ATHANAS


jason athanas 1/26/2009


Posted January 26, 2009 by jayauto in BMW

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