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.