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MSD80 to MSD81 Upgrade for N54 Engine

Basic Information

BMWs one of the best engines, model N54 was used in

  • BMW 135

  • BMW 335

  • BMW 335is

  • BMW 535

  • BMW Z4

  • BMW X6

N54 Engine had two versions of computers managing it, MSD80 and MSD81,

Other names of engine computer are:

  • DME - Digital Motor Electronics

  • ECU - Electronic Control Unit

  • ECM - Electronic Control Module

In this case, It's all same, We prefer to call it DME.

Problem Description

MSD80 has potential problems that are likely to happen:

1) the First problem is MOSFET failure

MOSFETs are electronic components on the MSD80 board, that do fail due to age or high performance,

and when one of them fails,  it causes the car to misfire hard and go in limp mode

With bad MOSFET, either the first bank is misfiring or the second bank

In case of bank 1 misfire there are these errors/codes:

  • 29CD Combustion Misfire, Cylinder 1

  • 29CE Combustion Misfire, Cylinder 2

  • 29CF Combustion Misfire, Cylinder 3

  • 30BA DME digital motor electronics, internal failure

In the case of bank 2 then there are these errors/codes:

  • 29D0 Combustion Misfire, Cylinder 4

  • 29D1 Combustion Misfire, Cylinder 5

  • 29D2 Combustion Misfire, Cylinder 6

  • 30BB DME digital motor electronics, internal failure


Very often, along with MOSFET, there is a burnt ignition coil, We strongly recommend replacing it

2) PSUs on board (Power Supply Units, one per bank)

Each PSU feeds electrical components of a specific bank.

PSU failure is rarer than MOSFETs problem, but when it happens you get the same symptoms as in the case of failed MOSFET, with the same error/codes.


The updated version of the engine computer, MSD81 has no weak points, Comes with stronger MOSFETs and PSUs.

We offer programming, aka matching MSD81 instead of MSD80 to your CAS module, i.e. basically replacing MSD80 with MSD81.


How it works

We have MSD81-s in stock, Our turnaround time is the same day or the morning of the next working day, it depends what time package is delivered to us.

To do this upgrade, You will need to send us: 

1) CAS module

2) 1 working Keyfob (without metal key)

If you want us to code injector numbers to replacement DME MSD81 then:

3) Injector numbers

If you don't know how to read injector numbers that is not a problem, 

If your original DME MSD80 is responsive and you can read codes, you can read Injector numbers by tools like INPA or BimmerGeeks ProTool.

You can also send the original DME and we will read injector numbers from it.

In case if DME MSD80 is not responsive, you can read injector numbers on injectors themselves.

These are the numbers we need:

CAS3 Module

CAS3 module looks like this:

You can find CAS3 module at this location, It's underneath steering wheel, on top of pedals:

** Please keep in mind, The shipping type you choose during checkout, is for return shipping only.

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