[cwelborn211]

Hey everyone!

My 2008 (2007 in the Door with MSD80) 335i was stuck in a cranking but no start condition 3 days after a Voltage Regulator went bad and the car was running at a high Voltage. Here are the codes:

2E30 - Injector 1 activation
2E32 - Injector 3 activation
2E33 - Injector 4 activation
2E34 - Injector 5 activation
2E35 - Injector 6 activation
30BA - Injectors 1,2,3, or DME, internal fault
30BB - Injectors 4,5,6, or DME, internal fault

Tested the MOSFETs for continuity and the multimeter didn’t beep. Assumed they were good.

Fast forward 4 years and a new battery later, and the car magically cranks sometimes but no fuel in Bank 2 (Cylinders 4, 5, and 6 Are dead, no change when unplugging ignition coils. Codes are now:

29D0 - Combustion Misfires Cylinder 4
29D1 - Combustion Misfires Cylinder 5
29D2 - Combustion Misfires Cylinder 6
30BB - Injectors 4,5,6, or DME, internal fault

When it starts it starts immediately, then sometimes it doesn’t even try to turn over. It just cranks.

Pulled the DME out yesterday and measured the resistance between the MOSFETs. All injector Drain to Source readings were 500 Ohms. Drain to Gate were infinite resistance.

The Ignition Coil MOSFETs read infinite resistance for both source and gate to drain.

There were 2 other MOSFETs that read the same as the injector readings but I could not find online there purpose (Any ideas??)

I was under the impression the source to drain should have infinite resistance, my readings indicate a short between the two for 8 MOSFETs.

Can anyone confirm/deny my suspicions and have some insight on the 2 MOSFETs that are by themselves? Many thanks in advance!

[cwelborn211]

Any info would be greatly appreciated!

[Warishuku]

I read in some discussions here (comment 357) that these 2 mosfets are related to the boost control solenoids, not related to injectors or coils.

[cwelborn211]

Thank you for your reply! I could not find any ecu schematics, these measured the same as the other 12, maybe I’m not measuring impedance correctly or they cannot be measured while on the board. The only option I can think of is to send the unit to ECU Pro for them to test (Also test on their E90). If anyone could help with a reliable testing method while the MOSFETs are still on the board I would really appreciate it. The videos I’ve found do not seem to go in depth on the various faults inside these components. I’m guessing the ECU or Injectors are my issue, but I’d like to find the issue before throwing parts at the car! Any information would be greatly appreciated!

[GSB]

MOSFETs can fail short-circuit or open-circuit. It sounds as though your MOSFETs have not failed short-circuit. Measure them again with your multimeter set to the highest range of resistance and compare them again. They should not be "infinite resistance", especially when mounted in a circuit board with a load connected. You should see megaohms or less, and they should all read about the same.

These MOSFETs are designed to switch the load (injectors) to ground. The injectors should all have 12V on them when the engine is running, and the MOSFETs would pull them to ground for an instant each time they fire. Ideally, an oscilloscope would be used to check that each one is firing properly.

It is highly recommended that you replace ALL 6 injector MOSFETs with an upgraded part (same as MSD81) as soon as you see codes 30BA or 30BB.

There could always be something else going on too. An over-voltage situation might have damaged or shortened the life of other components in the chain, including sensors or other DME input components. For example, read the following excerpt from the BMW Training Manuals...

The ECM will also protect the Catalytic Converter by deactivating the injectors. If the ECM detects a “misfire” (ignition, injection or combustion) it can selectively deactivate the Final Stage output transistor for that cylinder(s). The injector(s) will not open, preventing unburned fuel from entering the exhaust system. The ECM controls the individual injector circuits resulting in deactivation of one or multiples. This will limit engine power, but protect the Catalytic Converter.

A bad sensor (or connection in the harness) could also cause the ECM to assume such a condition. Do you see any other codes recorded?

One more thing... if spark plugs are fouled or not firing, injector firing may also be suppressed by the DME. To check that the coils are working on 4, 5 and 6, you could pull those coils one at a time and use an old spark plug (grounded to the engine) to check while you crank.

[cwelborn211]

All cylinders are firing, I will get all multimeter readings and report back! I wish I had an oscilloscope, but unfortunately, I don’t have access to one right now. As far as the MOSFETs go, does polarity matter? I seem to remember getting different readings when switching the leads.

Other codes:

2ACC - DME Master Relay Shift Delay
2DED - DME Power Management closed-circuit Current Violation
2E8E - IBS Missing

I did replace the Fuse Box with the Master Relay inside.

[GSB]

Originally Posted by cwelborn211

As far as the MOSFETs go, does polarity matter? I seem to remember getting different readings when switching the leads.

Yes, polarity matters. Measure both ways, but, to be consistent, compare all MOSFETs with the meter connected one way, then compare all MOSFETs again with the meter connected the other way.

Originally Posted by cwelborn211

Other codes:

2ACC - DME Master Relay Shift Delay
2DED - DME Power Management closed-circuit Current Violation
2E8E - IBS Missing

I did replace the Fuse Box with the Master Relay inside.

Hmmm, these are more serious. I suppose a short-circuited MOSFET might cause a DME Power Management closed-circuit Current Violation, but you didn't find any that were blown short-circuit. it sounds as though you have other issues. There may not be anything wrong with your MOSFETs at all. It's possible that the 30BB code is a symptom of the others. IBS missing? Your over-voltage situation may have killed other stuff, or replacing the fuse box may have left something misconnected. What was the reason for replacing the fuse box? And are you sure you got an exact replacement?