I worked for over 30 years in a contract defense plant, on both commercial and military avionics. At first, the equipment we sold had what we called “monitor” circuits. If a circuit failed, it alerted the pilot to an unreliable piece of equipment. On one project, monitor circuit failures were a full 50% of all failures.
When they went to embedded microprocessor units, the self-diagnostic operation was called, self-test.
By far the worst problems were intermittents. If we hadn’t had contracts for service, some of those intermittents would have cost the customer a fortune. And, with avionics, one must be very careful about writing NTF (no trouble found) on the paperwork and sending it back.
When I bought my 2002 Sienna, that was my first OBDII car, and I was nervous about it. Then, once I realized what OBDII was, I said, “Hey, I can do that. It’s the same as self-test in my work.” Except, of course, in the avionics I had access to the software listings so I knew exactly what self-test was doing. In OBDII one really has to dig to figure out exactly what it is doing.
Eventually, I had an intermittent Evap problem. I knew from personal experience that intermittents like that could bankrupt me very fast, unless I was lucky enough to get a mechanic who had learned over the years exactly what could cause an intermittent evap problem. After doing all the usual stuff with the gas cap, I just waited and kept recording problems as they occurred. In some cases, it would go months without a failure.
Finally, someone on Sienna Chat reported the exact problem with the solution He had two Sienna’s so swapped parts until the problem moved over. It was probably self-actuating valves on the canister assembly.
I took the car to the McAllen dealer, and signed a waiver of guarantee, and had them replace the canister. I was happy to take responsibility for my decision, using my own money, much as for over 30 years, I used my employers money to learn.
Years have passed with no further failure on the canister.
When I posted this tale here at that time, someone said if he was told what part to replace, he’d hand them his tool box and tell them to replace it themselves. I think I told him what I’d do with his toolbox, heh, heh.
It was my money, and while I realize a mechanic may have confidence in his troubleshooting abilities, well, it was an intermittent and I certainly knew how hard they are to troubleshoot, even for the best troubleshooters. And, as i said, it was my money he was going to be playing with, not his.
) and at the end, finally looked at the hub. Yep. It’s the hub. Fortunately, all that was warranty so I didn’t have to pay, but it was an example of the unfortunate fact that some mechanics today rely on computers to do all of their diagnostics, and since there is not a “hub out of true” sensor, they were lost - and it’s those mechanics who will bleed customers dry replacing random crap until they finally, entirely by accident, stumble on the part that is actually bad.