Jay,
Scroll to the bottom of this page under Home Brew DTC Tool
K6JRF Auto Page
Build the tester and then pull and clear the codes on each module. You will probably have quite a few if they haven't been cleared in a long time. Focus on the codes that come back after you've cleared them all.
I used three large paperclips for my tester where the terminal ends plug into the 38-pin cannon plug. The schematic shows these as banana plugs. This tester is not difficult to build. I am not an electronics guy and I built it in about an hour. I've used it hundreds of times over the years.
If you don't want to build it, I think they are available on ebay.