There is a misunderstanding. You do not purchase an entire circuit; you diagnose it. I suspect you purchased a speed sensor. This is a real common mistake, and your mechanic is right. In fact, I do not read that very often. What he is referring to is diagnostic fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. First we have to inspect the wiring for breaks or grounded wires, and the connector terminals to see if one is corroded or stretched. Next, voltage readings will help to identify a wiring problem, but that is much easier when you have a scanner to view live data. When you pop in a new part that is referenced in a fault code, there is only about a fifty percent chance that part will solve the problem.
By replacing the part yourself, you spent a little money on a good suspect and saved much more on the mechanic's diagnostic time. Unfortunately this time it did not pan out, but you are probably still money ahead in the long run.
Friday, August 12th, 2016 AT 11:43 PM