Yes, you need a mechanic. As you can see, diagnostic fault codes never say to replace parts or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. In this case code 101 is just the starting point that tells the mechanic which circuit to look at. He will start with a visual inspection of the hose between the mass air flow sensor and the throttle body. It can't have any leaks. Next will be some electrical tests to look for corroded splices and connector terminals, and other wiring problems. Once everything else is ruled out, it may be necessary to replace the mass air flow sensor.
Most of this testing requires a scanner to view live data to see what changes while the mechanic makes changes within the system. He has to see how other sensors react during these changes. For every fault code there is a long list of test procedures he has to follow. It takes pages to list all the steps.
One other less-known problem is the Engine Computer constantly runs many self-tests, and some are run only at specific times, and those tests rely on the results from various sensors. If one of those sensors has a fault code set already, the computer knows it can't rely on its results, so it suspends some of those self-tests. A second problem could pop up that does not get detected, that is, until the first problem is fixed. THAT'S when the second problem is detected for the first time, and the mechanic has to tell you more diagnosis and repairs are needed. That is very frustrating for mechanics and car owners. He had no way of knowing about that second problem when he gave you the estimate for the first repair.
The problem of repairing this type of fault code is most people resort to trial and error, and replacing random parts. First of all, that adds a lot of new variables, mainly with new sensors. The computer has to learn the characteristics of each new part, and sometimes that procedure doesn't take place when the original problem is still there. A new part could actually make the engine run worse, or it could run better because the computer purposely ignores a known-defective part. Second, replacing random parts is the most expensive way to diagnose a problem. Too often we read where someone spent way more on parts than they would have spent having the problem professionally diagnosed.
Sometimes you can make an agreement with a mechanic to have him diagnose the problem, then you can replace parts, but that leads to a whole lot more potential problems, particularly when that new part wasn't the right answer.
Tuesday, January 27th, 2015 AT 4:20 PM