Getting Your Hands on the Right Manual
The 2015 BMW M4 comes with two distinct documents you actually need, and most people conflate them. There is the owner's manual that lives in the glovebox, which covers routine information like fluid capacities and dashboard warnings. Then there is the service manual, which is the thick book with torque specs, teardown procedures, and electrical diagrams. If you are doing anything beyond checking your oil level, you need the service manual. The owner's manual is useful but limited. I spent about forty dollars on a used printed copy of the service manual from a junkyard in 2017 because I needed the timing component procedure for the S55 engine, and at the time it was the only reliable source. That PDF version probably exists somewhere online now, but I never hunted for it. For the official documentation, BMW makes the owner's manual freely available through their website. You go to bmw.com, find the support section, enter your VIN, and download whatever is listed. It is free and usually accurate. The service manual, also called the Workshop Information System or WIS in BMW's internal language, is not something they hand out casually. Dealers have it through ISTA. Some independent shops subscribe to professional diagnostic software that includes it. Enthusiasts typically end up finding digitized copies through BMW forums, though the legality of distributing those is unclear and I am not going to link to any specific source. What I can tell you is what is actually in there and how useful it turns out to be. The manual covers the S55 twin-turbo six-cylinder in detail, which is good because that engine has some quirks. The N55 it replaced was relatively straightforward. The S55 is more complex, and if you are working on it blind, you will make mistakes. The manual shows the exact torque sequence for the cylinder head bolts, the correct tensioner adjustment procedure for the timing chains, and the special tools required for the turbocharger servicing. Without that information, you are guessing, and guessing with an S55 is expensive.
One thing the manual does not do a great job of explaining is the dual-mass flywheel inspection procedure. You cannot reliably judge its condition without pulling it out and checking the dampers visually. The manual mentions symptoms but does not give you a tolerance range. I learned that the hard way when I replaced a flywheel on my M4 in 2019, thinking the shudder at launch was just clutch wear. It turned out the flywheel had worn internally, and the new clutch started shuddering again within two thousand miles because I did not catch it the first time. After that, I always remove and inspect the flywheel whenever I am already at that point of disassembly, even if the symptoms seem to point elsewhere. If you are doing maintenance yourself and want the technical data, another option that works reasonably well is subscribing to a service like Alldatadiy or doing it through an independent specialist who uses ISTA. The dealer route costs more but gives you access to the same technical publications without the ambiguity of downloaded PDFs. I find that for simple things like brake pad replacements or air filter changes, the owner's manual is sufficient. For anything involving the valvetronics system, the variable geometry turbos, or the rear differential, I would strongly recommend having the service manual open in front of you. The difference between stripping a helical gear on the diff and doing it right is mostly about knowing which bolt is preload-adjustable and which one is just holding the cover on. There is also the vehicle-specific data that applies differently depending on whether you have the Competition Package. The manual notes the differences, but they are scattered across sections. The Competition Package raises the horsepower to 444, tightens the suspension tuning, and uses a different final drive ratio in some markets. If you are sourcing parts or adjusting settings, confirming which variant you have by checking the build sheet through your VIN is worth five minutes and prevents ordering the wrong components.
The manual is not perfect. The index is functional but not intuitive, and some procedures reference figures that are cut off or poorly reproduced in the PDF versions that circulate online. Electrical troubleshooting sections rely heavily on schematic diagrams that assume you have a working diagnostic tool. If you are just changing fluids and filters, you probably will not need those sections. If your check engine light is on and you do not know why, you will wish you had the full ISTA setup rather than a static PDF. I keep a printed copy for reference on the bench and use ISTA on my laptop when I need live data, and that combination has worked well for me over several years of working on this car.
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