I retrieve the codes according to mt "Haynes" manual. After driving, turn off the engine, turn the ignition to on, then off, then on, then off, then back on and leave it. The codes show up as flashes of the "check engine" light. Is there another way to retrieve the codes? If I buy one of the retrievers from JC Whitney, will it work on other vehicles???

Just a used 4 cyl '94 Wrangler