MSS54HP ECU Problem After H-Bridge Mod

[Mpoweralem]

Hello everyone,


I’m having an issue with my MSS54HP ECU and I’m hoping someone here might be able to help.

I soldered an H-bridge to the ECU as described in the common guides, but it did not work. After that, I switched to a Bosch H-bridge, however the problem is still the same.

Currently, when the ignition is switched on, the ECU continuously drives the CSL throttle valve. If I remove pins 8 and 9 from the ECU (throttle motor pins), everything behaves normally and there are no issues. But as soon as I reconnect the pins, the throttle is immediately activated automatically, and there seems to be very little current output from the ECU.

Because of this, the car is currently being driven without the throttle connected.

I would really appreciate any advice or ideas on what could be causing this.


Thank you in advance for your help.

[terra]

Sounds like a short circuit somewhere. Using the correct H-bridge for sure?

[karter16]

I guess wiring would be another thing to double check - presume you've wired yourself and not using a CSL wiring harness? If so then would be worth double checking that as well.

[Mpoweralem]

Thanks for the quick replies.

The first time I soldered the H-bridge myself, but it didn’t work, so I had it re-soldered twice afterwards. There is now a Bosch 30348 H-bridge installed.

The wiring harness was properly crimped and connected according to the wiring diagram.

The problem only occurs when the flap motor is connected and I turn the ignition on – then the ECU voltage drops. Is it possible that something else got damaged? Unfortunately I don’t know what else to check at this point.

[Mpoweralem]

I uploaded 3 pictures.

• In the first one, I soldered it myself, but after that nothing worked.
• In the second, I had it professionally soldered, and the control unit worked, but the flap still showed the same symptoms as described above.
• Then I switched to the Bosch chip shown in the third picture. That’s the current status.

[karter16]

Is that the supply voltage to the DME that drops? That doesn't sound great.

Dumb question but just to make sure. This DME has the 0401 CSL program and tune binary loaded on it right?

Are you 100% confident regarding the wiring? A possible reason for the voltage drop could be that input and output pins are mixed up and being incorrectly drawn high or low.

[Mpoweralem]

When I cycle the ignition, I initially see normal voltage. After a few seconds, the voltage doubles and the flap actuator starts moving automatically.

I’ve checked the wiring carefully and I’m 100% confident it’s correct.

If I remove pin 8 and pin 9 from the flap actuator motor, the voltage stays normal permanently. As soon as those pins are connected again and I just switch the ignition on, the flap is actuated automatically.


Yes, the full 0401 CSL software and tune are loaded on the DME.


Thanks a lot for your help, I really appreciate it.

[karter16]

Hmmm there's a diagnostic mode in code that repeatedly toggles flap state between open and closed. Are there any changes that have been made to the 0401 tune or is it fully stock?

[Mpoweralem]

Such a stupid mistake on my part.

When I switch on the ignition, it is actually normal that the flap starts adapting and moving. I panicked immediately and turned the ignition off again.

After watching some CSL flap test videos where it behaves exactly the same way, I let the ignition stay on — and guess what, it stopped moving by itself. Then I went into Tool32 to actuate it, and everything worked perfectly.

That means I actually did everything right the last time as well.

Still, thank you all very much for the quick replies and help.

Top community! 👍

[karter16]

Nice one! glad you were able to get it figured out.

[Mpoweralem]

I only have this issue since I installed the HP control unit with the CSL software: the green indicator icon doesn’t show up on the gauge cluster when I turn the lights on.

Does anyone else know this problem or has experienced it?