Interpreting multiple codes

[94q45t]

My recent Nissans have been a 97 & 00 Maximas, 01 Pathfinder (SE-2WD auto), and 94 Q45. One thing the 00 Max and the 01 Pathie have both done is to throw multiple codes simultaneously. In the case of the Max, it stranded my son and had to be towed I was out of town and he owed it to a dealer who said the wiring harness needed to be replaced - $2500 - (never in my life...). I told my mechanic to come get it, and he reported a bad MAF. He replaced it and the car was fine. I took it back to the dealer who showed me a report with, oh, 10-12 different codes on it, but the car's been fine ever since and passed two emissions.

Sometime later, the Pathie did the same thing. The emissions folks said it was a bad IAS, which I replaced. Didn't help, but it was due for the 100,000 tune (new plugs basically), so had that done. The mechanic said it was throwing a code indicating a transmission issue which required a specialty shop. Before we got there, the CEL went out, never to return, and it passed emissions, and currently, it's not throwing any codes.

So question for all you trained Nissan techs out there, are ECU codes typically this hard to interpret? Friends with newer Cadillacs tell me this is a constant nightmare for them, and very expensive if you can't do your own work. WE do a lot of work with computers, and in that world, error codes are clues, but rarely are they reliable for specific rouble causes. Same thing here? Thanks!

[ARKQX33V6]

Multiple codes often mean nothing, but can mean everything but if not related can be a bus error and be just the first code entered. But it takes a bit of smarts. Examine the codes, what do they mean, are they relates and could they be related.

Eg A transmission code related to 1, 2, 3 or 4th gear related to a TPS code related to an O2 sensor. After looking at all codes it could really mean the TPS was intermittent and came open or WOT telling the transmission your in the wrong gear...really