I believe after reading this entry, you will get 100% confirmation:

  • the reason for the error message 30BA/30BB is not an “accident”, but a constructive defect of the DME;
  • the replacement of the damaged spare part to the same part (even more powerful) is not a solution. The installation of the protection elements (as described here) of low-side MOSFET switches is critical.

Today’s patient: E90 with an N53 series engine. Have to admit – the owner of the car is not particularly demanding to the performance of the car: individual misfires and vibration of the engine did not confuse him. Even with an active error message 30BA (with 3 cylinders disconnected) he drove more than 100km till the service. Yes, the car was “slightly less responsive”, but otherwise – no problems!

Yes, the DME error message memory has a full set with error messages: regarding the plausibility of the HPFP (obviously, some injector has started to leak), error messages regarding fuel mixture (obviously, when the injectors stopped to leak when the engine has warmed up, fuel adaptations turned out completely incorrect), for granted – misfires, etc.

Here, also the tests of the chemical efficiency of cylinders – incorrect. Obviously, the injectors are not short of problems:

Here, leaking of the injectors in idle:

Without illusions – several injectors have serious problems.

The repair of the car I started with eliminating the causes of the error message 30BA. When this problem will be eliminated, DME will turn on all 6 cylinders – we will be able to continue diagnostics of other problems (including injectors, ignition system, fuel mixture).

1. Performing diagnostics of DME, I determined that the low-side switch of the injector of cylinder No.2 is damaged. IRF644 transistor was replaced with SiHB30N60 (for this transistor Uds = 650V as opposed to 250V for IRF644).

In the picture: the low-side switch of the cylinder No.2 has been replaced.

2. DME restored the performance of all cylinders, but when the re-adaptation of the engine was performed, DME repeatedly turned off 3 cylinders, the error message 30BA was recorded in the error message memory. Yes, before recording the error message the performance of the engine was far from perfect (what is not a surprise, taking into account the condition of the injectors and other systems), but – what happened again?

3. Performing repeated diagnostics of the DME, I determined that this time the low-side switch of the injector of cylinder No.3 is damaged. Transistor was replaced with SiHB30N60, and DME was subjected to more serious testing:

a) heating of the low-side switch was checked, using a thermal camera. Here is the result:

Low-side switches are in the center of the picture, in the marked area. As you see, none of the switches is warming un increasingly. Increased warming-up could be due to several reasons, for example, incorrect management of the switch, leakage between its Drain and Source; defect of load (in this case – injector: increased leakage of the current), also – due to partial damage of the MOSFET itself.

Technical note: high-power MOSFET actually consists of 4 .. 20 MOSFET crystals of lower power, which are inserted in one case. If any of these cells are damaged (and damaged in such a way, that the connection is broken, not creating the short-circuit), the good cells continue to work. But, as after the damage the number of MOSFET cells has decreased, the performance of it also decreases (including – Rds on and heating of the transistor increases).

b) the signal of all 6 low-side switches was checked. Signal – correct, no objections.

In the picture: MOSFET of cylinders No.2 and No.3 replaced:

4. After several motor hours, again 3 cylinders were turned off, in the DME error message memory again the error message 30BA was recorded. This time the low-side switch of cylinder No.1 was damaged!

In the picture: a low-side switch of cylinder No.1 replaced

And this time – the overvoltage protection for all low-side switches installed.

After installing the overvoltage protection, DME works without problems.

Yes, you understood correctly – SEQUENTIALLY all low-side switches of the 1-st bank were damaged. At the same time – some moment after repair DME worked correctly, MOSFET signals – were correct. In my opinion, it’s completely clear: in this case, we can not blame anything else (for example, only injectors), not DME. Even if we theoretically assume that suddenly sequentially three injectors of the same bank were damaged, the question – why the high-side switch of the management of these injectors was not damaged?

Yes, if knowing, how this DME is built, it is clear for me, why these low-side switches are getting damaged (more info here).

One more nuance: for this defect, exactly the error message 30BA dominates (the problem of exactly the 1-st bank). But both banks of the engine are with identical hardware, what also is not normal!

I think, even the most skeptical person has to agree, that in this case, DME is one to blame in these troubles. As already mentioned before, the low-side switches of these DME’s are getting damaged by the defects of the injector or its connection (in addition – one injector or its connection defect can damage the low-side switches of the whole bank sequentially), the undervoltage problems; cutoff operation (due to leaking of fuel or misfires), when the result is turning off the injector.

These DME’s have a construction defect, which is intensified by the software bugs (due to them the error message 30BA and 1-st bank dominates).

And finally: useful external link:



Here, the management principle of the piezo injector (image from the link mentioned above):


Pay attention to the low-side switch (on the right side, on the bottom). In all work cycles, it has to be open! If this condition is not fulfilled, the damage of this switch is inevitable!

Here, both overvoltage protection solutions displayed (mentioned in previous entries of the blog):