Can't Feel My Overdrive!


#1

My 2000 Buick Century 3.1L doesn’t seem to have it’s overdrive upshift any more. Would I be able to hook up an aftermarket tachometer to this engine? What do they get connected to, a crankshaft position sensor perhaps?


#2

You could, but the money would be better spent having the computer scanned for fault codes, getting the tranny serviced, having the engine serviced, and other activities that ensure that the engine and tranny are operating properly… or find clues to why it isn’t.

The assumption that the upshift is a response to only the engine’s RPM is erroneous. Thus, using only the engine’s RPM to try to diagnose it will be counterproductive.


#3

I agree. Just get it scanned. There is a trouble code for OD and a solenoid for it that could be shot.


#4

+1 for both comments.


#5

I suppose you could install an aftermarket tach but the time and effort would surely be more than the $100 for a professional scan and road test with data recording and diagnosis of any failure. You may be able to determine whether or not it is working but that still wouldn’t tell you why.

I suppose if you have a complete wiring diagram, service manual, good electrical meter, and a lot of patience you could figure it out. It’s not really cold where you are is it? OD is often locked out under very cold conditions to hasten the rise to operating temperature. Other than that it could be a broken wire, a faulty electrical solenoid, low fluid level, mechanical fault in valve body, pump housing, or torque converter.


#6

Thanks for these comments folks. I’ll have it checked for trouble codes.


#7

“The assumption that the upshift is a response to only the engine’s RPM is erroneous”. This is true, but a tachometer would tell if the overdrive was working. Probably not worth the money, time or effort.


#8

A quickie way would be to ask around among people you know to see if someone has any kind of scantool capability - on the does live data. Most will do the RPM output.

Of course, you’ll need to get the scanning done either way, so I suppose it doesn’t matter much.

Do note that there are plenty of things that can cause the transmission to misbehave, but that have nothing to do with the transmission - e.g. TPS or MAP sensor issues. If you do have it scanned and want to ask for feedback, make sure to report any specific error codes that were read (format: “P0123”), and any other testing that was done (e.g. solenoid acutation, line pressures…)


#9

On my Riviera I knew it wasn’t going into OD because the RPMs were 3-400 higher at highway speeds than normal. So instead of running at 1800 at 70, it was more like 2200. Plus of course the Riv had on board diagnostics so you could check and see if the solenoid was being energized. You kinda have to know history though to know there was a problem but still there should be a final significant drop in RPM-but then just listening to the engine works too.