Oxygen Sensor diagnosis - lessons learned

Just wanted to share my experience here, hopefully can help someone out in the future:

At 56,000 on the odometer, my Service Engine Soon (SES) light came on, no other symptoms, car ran and started fine several times. Used the Peake tool, got the following 2 codes:

E 10 PreCat oxy sensor aging, Bank 1
E 11 AfterCat oxy sensor response time, Bank 1

Ok, easy enough, will replace sensors, see what happens... Best price I found for sensors (ordered all 4) was at BavAuto, about $350 with removal socket, replaced the 2 pre-cat ones, cleared codes, but they both came back again. At this point, decided to take the car to a new shop that just opend up down the street, since spent enough time on the pre-cats, the post-cat ones looked tough, so...

They connected their $30,000 analyzer up (sorry, forgot make), and the code read indicated malfunctioning MAF Sensor! Also, the tech pointed a vacuum leak in the rubber elbow past the MAF Sensor, next to the engine, which he said was very common, but generally would not throw a code. I allowed the shop to order and replace both parts, sure enough, codes cleared and stay cleared.

Lessons learned:

1) Check for vacuum leaks, apparently relatively common due to age and high temps under hood.
2) According to two BMW mechanics (different garages), the MAF Sensor fails more often than O2 Sensors, especially if using oil-lubricated filters (i.e. K&N, Dinnan).

Also have to give good review to German Auto Group in Springfield, VA, just opened, have the lowest labor rates around in the DC area, also do work on Saturdays, nice shop, easy to deal with

I had similar codes when using the Peake at first following the instructions to turn the ignition on first. Later had trouble getting codes and read the trouble shooting section. Said E 10 may be an error code! Said to try plugging in first then turn on ignition. When I did this, I got table 19 and code 41 for intake cam sensor! Try this procedure and see if you get similar results.

That's excellent advice, I never assumed that I was getting an "E" - error code, since the Peake tool worked for service and oil interval resets as detailed in the instructions.

Unfortunately, the codes were reset when the MAF was replaced, but will certainly refer to the troubleshooting section of the manual next time anything pops up.

Originally Posted by Paul325Ci

Also, the tech pointed a vacuum leak in the rubber elbow past the MAF Sensor, next to the engine, which he said was very common, but generally would not throw a code.

Past the MAF? It sounds like you are talking about the elbow that goes to the throttle body, and the small neck that normally cracks goes to the idle valve. If he told you that normally doesn't throw codes, you need to find another shop to go to.