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Need some non-W116 technical advice


Over my years here I've learned to rely on the scary amounts of Benz related knowledge you folks bring in, so before I go searching even deeper on other sites here's a question - does anyone happen to know if it's possible to test the electronic throttle actuator on a W124 off-car? If so, what's the inputs it is expecting - especially the actuator motor. I know the inputs it's supplying to the ECU, so that's not an issue.

I've had trouble with mine - the usual, crumbled insulation - and replaced it with a new VDO part, but have since rebuilt the old one and now just need to test it before I declare success and call it a day.

What's confusing me is that the actuator motor is just a dumb DC motor with a 30deg, physically limited, range of movement. If it were a servo I'd give it a DC power supply and a PWM signal to control speed and direction, and off we go. I'm guessing it has direct PWM drive from the ECU, and works in an on/off fashion rather than continuous control. There's a ton of information on how to rebuild one of these (which is dead easy), but none on how to test them other than putting it back on the car which I can't do.

I was hoping to build a test rig on top of a micro-controller.

The part number is A0001416525, non-ASR M104 - as seen below during the rebuild.

...and while I was re-reading what I've written, the "you dumbass" bulb went on. It might be a dumb DC motor, but it works in a closed loop system using the throttle plate position sensor as an input into the ECU, which in turn controls the PWMed supply voltage. So, unlike a typical RC servo which integrates all of that, here it's done in the ECU.


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