Look at the article in the dIY section on evaluating engine controls. It explains impulse counting. Yes, you have the basic concept. Trigger the response and count the blinks.

This transition period where some systems were impulse and some digital really messes with some techs. I had a car in not long ago that had been told it needed a control unit and something else on a SRS problem on an E420 (124 car). I started out with a scanner and couldn't get communications. Because the car came with a known diagnosis, I let myself stray and tried to prove a negative.

I spent some time verifying that the SRS controllr was properly powered (turned on) before it hit me that this was an impulse system. Got my impulse counter and quickly pulled a code for drivers airbag squib, which as in this case usually means clockspring arrangent beneath the steering wheel.

Whoever had made the original diagnosis condemned the controller because he couldn't get communications with the scanner. The whole repair was somewhere around $200 not the couple thou they had been told. Actually a fairly easy mistake. It will be nice when all cars are newer than 96 for us techs.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician