I'm glad it's running well again. Hopefully he did write down the exact code or codes he read before clearing. The generic OBDII codes (the minimum codes mandated by the EPA) will still tell you plenty. P0300 through P0316 are the ones in misfire. For example, P0304 tells you that cylinder four is misfiring, and P0313 says you have misfire with low fuel. So if the car's computer only stored a P0304, the mechanic can switch the number four and five wires and then see if P0305 is generated.

It is important to record the codes before he clears the codes out of the computer. If the engine light comes on again tomorrow and there are different codes, then he has two pieces of a puzzle: the earlier codes and the later codes. The second one is important for you. Say the mechanic tells you that he read P0172 (too rich) and P0304 (misfire on cylinder four). He changes the wires, cap, and rotor and clears the codes. Tomorrow, the light comes on again and you bring it back in. Same codes, so he now tracks down a vacuum leak and charges you another $150. At that point, I would tell him to put the old wires, cap, and rotor back on because he misdiagnosed the problem yesterday AND he had enough information to look for a vacuum leak first.

I'm not asking you to understand all of this. The point is that keeping a record of these codes can be an excellent way to reduce your costs on subsequent visits and a way to legitimately question a mechanic--even if you don't know much! So, if not this time, make certain taht in the future he writes down any OBDII codes (or DTCs) on your receipts.

Optimist