S54 O2 Sensors — Deciding Not to DIY

BMW S54 Engine

Recently my 2006 E46 M3 started throwing a code signifying a problem with one of the oxygen sensors in front of the catalytic converter (pre-cat). The S54 engine in the E46 M3 has four oxygen sensors, two in front of the catalytic converter and two behind.

Initially I thought this was a chance for a relatively straightforward DIY.  I replaced the pre-cat sensors on my 2002 E39 M5 in 2011 and it wasn’t very difficult. There was also a detailed video from Bavarian Autosport on exactly how to replace the oxygen sensors on the M54 BMW engine found in many BMW models. BavAuto is an authoritative source for DIY information and I hoped the instructions would hold for the S54 engine in my M3.

Unfortunately it quickly became clear that the process for replacing the sensors would be very different than either my previous experience or what the video showed. The BMW S54 engine doesn’t share much with the M54, having evolved not from the M54 but from the S50B32 engine that powered the later versions of the Euro-spec E36 M3. Reviewing threads on M3Forum.net indicated that a lot of parts would need to be removed to get at the pre-cat sensors, and even more importantly I couldn’t find any step-by-step instructions about exactly how to proceed.

The S54 engine is widely hailed as the finest non-turbo 6-cylinder engine ever made by BMW. The E46 M3 was produced in significant numbers, and the engine powered a few other BMW models as well. So I was surprised that this information wasn’t out there. It wasn’t available from BavAuto or from Mike Miller, the DIY columnist for Roundel and Bimmer magazines. Gordon Arnold, aka “Bavarian Otto” at BavAuto, said he’d consider adding this to his 2016 DIY video production calendar. That should help the next guy, but not me.

So I’ve decided to bring this job to my independent mechanic. I will be purchasing the sensors directly to avoid the obscene BMW markup. Since I’m paying for the labor and the car is 10 years old, I’m having all four sensors replaced. Purchasing the sensors myself will save over $400.

This is the first post I’ve written about a procedure I’m not doing myself. But I want to keep it real with my readers – sometimes DIY advocates get too doctrinaire and advocate doing all work yourself, no matter how difficult or time-consuming. Unless you’re a professional mechanic, it’s smart to stay humble when it comes to working on your BMW.

Without clear documentation, I’m more comfortable bringing this job to my indie. He’ll treat it like it was his — because it used to be!