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      04-15-2015, 03:51 PM   #1
DAT240
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M3 E93 pre-cat O2 replacement

My M3 has 125K km - engine light appeared, checked with the OBDII. The code read P2414 - bank 1, sensor 1 O2 sensor exhaust. I searched the forums, some info exists, but I'm posting this in case anyone else needs to change theirs.
First of all, I'm in Canada, so $ are in Cdn and measurements metric. I qualify for the seniors discount in most places, so no whining about working under a car with no room to move. Suck it up.
These are the pre-catalyst sensors. Bosch part number BOS1828336. $340 ea from the stealer, $233 ea online. Likely cheaper in the US, but that's the price I pay for living in the great white north. Bought 2 because I'm only crawiling under there once. The pre-cat sensors are labeled as "1" on the drawing. They are located in the exhaust, under the car, right before the catalytic converters.
You'll need a 7/8" wrench. Due to the cramped location I don't think that an O2 sensor socket will fit. The wrench worked perfectly.
I put the car on ramps, proceeded to move the cover around the transmission. Lots of small fasteners, not all the same type, so be anal and keep them separated.
The drivers side sensor is accessible. The connector comes apart by pressing the plastic bar down and pulling the connector. The sensors were not seized as i feared, likely due to the anti-seize compound. (The new sensors came with it already applied). Disconnect the plug first so that the nut will turn (duh). The connector is held by a U shaped clip. Slide the connector out of the clip, and there is also a clip for the wire. Reinstall the new sensor in reverse order.
The passenger side is the problem. There is a shield which prevents the connector from sliding out of the U clip. To do this "the right way" you probably have to remove the large aluminum plate under the engine bay, remove this shield, etc. I was able to loosen the bolt holding the shield in place (not too much or you'll be removing the big shield to find the bolt), then with a small pry bar I pushed the shield aside and was able to re & re the connector. No small children should be within earshot while you are doing this.
I reinstalled the transmission cover, zeroed the code with the OBDII. It has been a week of hard driving with no alarms. And I'm sure that the engine is running much better than before I changed the sensors. They definitely mess with the engine management functions. I can't comment on any improvement on the mileage (usually averages 12 L/100 km) because spring is here, the top is down and the engine just wants to go.
So, not a difficult fix, but a hoist and smaller hands would have helped. I worried that there were underlying problems, but my research indicates that the O2 sensors just wear out. In the meantime I'm happy to have my baby back.
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      04-16-2015, 01:58 AM   #2
Gbyleveldt
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Nice, thanks!
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