Progress! The connector is indeed quite easy to remove if you just pull the tab the right direction.
I took the module indoors and popped it open on the bench. It's not sealed at all, just 4 T10 screws at the corners will open it up.
Good:
- Very easy to implement Dieselbenz's fix internally!
- Easy to grab regulated 5v power
- Easy to cut traces to take over outputs
- Lots of room for an ESP32 on the top side of the board
Bad:
- No discrete output transistors to easily drive by cutting traces. They look to be on the covered Bosch daughterboard. The low voltage gate drive signals are probably available between the CPU and daughterboard though, making a full trace and reimplementation a summer project unless I wanted to build a more complex PCB.
- Windowed EPROM, despite the sticker, I wouldn't leave this board outside of the box for too long if you want it to keep working.
I would have implemented Dieselbenz's fix this evening and unplugged the EGR valve except for one issue... I promised a friend I would pick her up for a ride in my Mercedes tomorrow
I also have to confirm pin numbers with a meter.
- EGR output has to be 18
- MAF, the 602's sensor does not have 5 pins, and it's not documented on the drawing which resistor is the thermistor and which is the vane. I am suspecting pin 22 from the drawing, but will have to check with a meter.
I'm not sure if I want to do that 12v pullup or just put it to 5v, as the MAF input appears to be limited to 0-5v. However the diode will only conduct when the EGR output pulls it down, making the actual pullup voltage fairly irrelevant as long as it's higher than the MAF output. Either 5v or 12v should work.
Was 12v just used for convenience, or was it needed because the ECU checks the valve is floating up to 12v in between pulses or something?