It sounds so easy — just bring up the trouble codes for your later model car, buy the part, put it on and off you go!
Except that it doesn’t work that way. Identifying the code is helpful, but it’s only the first step.
What the code really tells you is that the computer is getting information that is not normal from a specified area. It might actually be a major component, but it might be something as simple — and sometimes as hard to find — as a loose wire, or a corroded connection or ground.
It might be something else that is not triggering the target gizmo. Could be a vacuum line, or a crack in a hose. It could be a water, or oil, or fuel leak that is seeping onto somewhere other than where the leak actually is.
It could be a loose bolt that is allowing something to be out of its proper place or alignment. It could be a bad fuse, or a bad connection in the underside of the fuse box. If a fuse is blown, that just pushes the question back to the components connected to that circuit.
In other words, you’re not dealing with a single cause — you’re dealing with a whole system, with a varying number of places where something could be messing with the information that the computer is getting. And some cars are known for having failures in the sensors and monitoring system itself.
Many of the same problems are possible in a pre-computerized vehicle; but instead of a code to chase, you are working with what appears to be a failed component. The approach is the same: before dismantling anything, check for things that are probably beyond their useful life.
When you do find an obvious or suspicious defect, remember that there can always be more. Over the years, I have had techs tell me that “It’s got to be this”, or “I’ve already done this, so it’s gotta be that.” My answer is always “There can always be something else wrong; it is possible to have measles and chicken pox at the same time.”
We just finished a job that came in with everything pointing to the carburetor. Turned out that the carb was fine, but everything that connected to the carb had something wrong — clogged vacuum lines, contamination in the fuel, bad wiring on gizmos that work off the carb. Poor carb didn’t have a chance.
Familiarity helps, as well. There’s always a first time we see a particular failure, but the more familiar we are with a specific car or system, the better chance that we’ve already been there, done that, learned something.
There are some things a technician can figure out the first time, but there are other things that have odd things going on that the technical info available may give you a valuable shortcut to; or, there may be things in a particular car that may be a fairly uncommon add-on that is not mentioned anywhere.
We found something like that just a few days ago. The factory-recommended procedure called for loosening a couple of mounting bolts in the suspension to provide clearance for the item being replaced. One of the bolts was easy; the other one turned out to be underneath a part that is part of a a rare, optional system that had to be partially dismantled to get to the bolt in question.
There isn’t a computer yet that can match the one between an experienced tech’s brain and fingers!