On Sun, 1 Dec 2019 15:24:46 -0500, Ralph Mowery
wrote:

In article ,
says...

I do similar - but usually I "test" the relay (or whatever) to either
prove it IS the problem or it IS NOT the problem. This is because I
don't always have the replacement part available, and in most cases if
I get the part and it is NOT the problem it is not returnable - and
I'm stuck with it. If IDO have a "Known Good" part to swap in, it IS
(generally) the quickest way to prove the fault.



If I had to buy a part, I would try to make sure it really was bad.
Where I worked, we had thousnds of spare parts as the plant needed to
run 24 hours a day, nonstop. Usualy had one or more replacements for
most everything. Those were small realys and I would usually put one in
my pocket before I left the shop as it was in another building. I also
carried some test equipment just in the rare case it was not that part.
There was another part that was known to fail so took one of those with
me, but as it took about 20 minuits to change it out, I would run a few
tests to determin if it was the problem.

I did have a Toyota that started running rough. As I am not a very good
car mechanic, I threw a few logical inexpensive parts at it. Plugs,
wires and coil. The hint page on Autozone pointed to a mass air flow
sensor, but it was around $ 500. Took it to the Toyota dealer thinking
they could test it. Two weeks or more later they finally decided it was
the sensor and put in a new one. Not sure what kind of mechanic they
had, but did not seem to be much of one.

Then there are the ones that do not have a clue and do not seem to know
what to do, so they just change parts blindly.
The MAF on the 22RE and 4MGE as well as many others was actually
REALLY easy to test with an ohm-meter and your finger.(I was Toyota
service manager for 10 years from '79 to '89 and toyota tech back in
'72