BMW M70 / M73 / N73
V12 · naturally aspirated · petrol · 1987–present
Also known as: m70, m70b50, m73, m73b54, n73, n73b60, s70, s70b56, bmw v12
BMW's naturally aspirated V12 — the 5.0 M70, 5.4 M73 and 6.0 N73 — in the 7 Series and 8 Series.
⚑ The M70 and M73 are two straight-sixes on a common crankcase, and that is not a metaphor. Each bank has its own engine management, its own throttle body, its own set of sensors and its own idle. A fault on one bank leaves the other running normally, so the car can be running on six cylinders and feel merely rough rather than broken.
So diagnosis means treating it as two engines and comparing them. Fuel trims, live data and even the ignition system are bank-specific, and a reading taken from one bank says nothing about the other.
The N73 is a modern single-ECU engine with Valvetronic, and almost nothing about the older pair transfers to it.
Age and complexity are the practical problem rather than any one failure: twice as many coils, twice as many sensors, and a wiring harness whose insulation on the earliest cars degrades. The N74 twin-turbo that replaced them has its own page here.
Cars fitted with this engine
2 generations, across 1 make. From the authored catalogue — an absent car means the catalogue has not reached it, not that the engine was never fitted.
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Posted about this engine
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about M70 / M73 / N73.