Was wanting to find out if on the cars with the OBDI scanning, that if there were codes from some kind of failure. Then the particular problem was corrected per se. Would the diagnostic system continue to hold the codes or would they clear out on their own?

I think it goes both ways - some would clear and others may not. It's easy enough to erase the codes to be sure it's gone.

I picked up the items from RS to build the code reader. Was not for certain what to put it together on? Wanted to see what some others here may have used. I have never used one, and I thought it would be good to have one.

I used a generic small plastic box and drilled holes for the led, button switch, and test leads. I built mine using this as an example.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Thanks for the information on the mounting of the tester! I got it put together & tested it. With the ignition on position 1&3 for the 201 I got a single flash. Looking at the code list it saying no trouble. I would have thought it would have some bad boys stored from previous issues? I tested with ignition switch in on position. It showed on or in the engine run idle speed. I presumed from reading it either one is acceptable for testing??

Just for kicks, you might want to unplug your Engine Coolant Temperature Sensor, start the engine, after minute or two turn it off. Plug it back in, then do the LED test again to see if you get 3 flashes. If you do, then clear it...that way you'll know you are storing DTC's and your tester is working.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

I did some re-testing today! 1. Continuous Fuel Injection using socket #3
I continued to get just 1 flash. I then pulled the coolant temperature sensor & started engine for a few minutes. Then I checked it again & I got 3 flashes. So, I cleared it out. Then I tested 2. Continuous Fuel Injection (MAS Controller) socket 14 I got code 4. Output for oxygen sensor heater control defective
& code 6. Output for kick down control defective. So, I then reset all the registers. I drove it a few times today on short trips, & then I did a follow up check. I didn't show anymore codes on either socket after that. I wasn't for sure if trouble showed on the MAS Controller socket if that meant it was bad or just related to the different components, as well? I wasn't for sure on the fault codes which ones pertain to the Crank or Timing sensors?