Trans/speedo SES... PROBLEM

[jamesshall]

I picked up a very clean 1995 Grand Am SE for a great price about one month ago. Everything is in GREAT condtion, but the transmission and speedometer are having issues. I think their issues are related somehow.

Problem(s) #1 -
If I am driving the car and come to a stop and then begin to accelerate I have to go very slow or the speedometer won't work. If I take of normal the speedometer remains at 0mph. If I take off slowly, the speedometer reads 0mph until I reach about 20~25mph and then the speedometer kicks in and starts working.

If at ANY time (from a stop or while rolling) I decide to accerate quick enough to where the tranmission would normally downshift, the speedometer drops to 0mph and NO downshift occurs. If I accelerate hard from a stop and ignore the 0mph, the car will stay in 1st gear and NOT upshift while the speedometer sits at 0mph. It will even get to the poin where the engine will rev so high that the SES light comes on. I have to let off the accelerator and wait for the speedometer to start working before it upshifts... the SES light goes off after I left off the accelerator.

If I ignore the 0mph readings that the speedo gives me and I drive as if the car was operating properly (not slow and not fast... just normal), the transmission will mess up. It seems like the problem has something to do with letting the speedometer read 0mph when it reaches the shiftpoint for 2nd gear. If the speedometer is reading 0mph when it comes time for it to shift into 2nd - it WON'T shift. If I back off the accelerator it will allow the speedometer to come back on the car upshifts, but by then it's too late and the tranny acts screwed up. I'll come to a stop light and then begin to accelerate, but the transmission won't be in first gear... it will be in 2nd gear and will not go back to 1st gear for the remainder of the drive. I usually will just manually shift the car into 2nd and just leave it there. The other alternative is when I come to a stop, I can turn off the car and restart it (I can do this as fast as I want... doesn't matter for how long the car is off). For some reason this will get 1st gear back. If I "baby" it by driving slower than a bluehaired grandma from stop through 2nd then I will have 1st gear for the whole the drive.

It seems that the problem is worse after the engine has completely wormed up.

I replaced the VSS on the tranny with a new one, but that didn't change anything.



Probelm #2 ---

I have seen the SES light come on a couple times, but it goes right back off. I would like to find out what error was being sent. This is a 1995 car and it seems like there is no reasonably priced scan tool for it. I just want to see what codes there are and I don't need a complete $700 diagnostic tool. I have seen these at Pep Boys and Auto Zone for about $30, but they don't have them for the 1995 Grand Am. From what I understand, the car is OBD-1 and is equiped with a plug that requires a scan tool just like OBD-2 cars.

[Flatrater]

Trans and speedo are related. Trans needs a speed input for proper shifting. I would bet the SES light is related also to the speedo. Your problem sounds like a problem with the speedo sensor wire on the trans, most likely it is broken inside the insulation. Pull on the wire if the insulation turns white the wire is broken there!

[jamesshall]

That's what I figured. I was going to try to run a wire outside the car and hook it directly from the computer to the VSS and see what happens. I also noticed that there are 2 wires on the VSS. I'm sure that one of them carries the signal back to the computer, but I don't know what to think of the other wire. Is it just a ground? Maybe I have a loose ground wire?!?!?!

[Flatrater]

Both wires go back to the computer. If you have a meter put it across the 2 wires key on engine off you should see 5 voplts on the wire. Next put one lead of the meter on sheet metal and the other on the wire terminal (don't jamb the lead into the terminal you can damage it) should see 5 volts on one wire and nothing on the other. If you see anything different than you have a broken wire.

[jamesshall]

Great! thanks for the help!

As I stated earlier I had already replaced the VSS. Over the weekend I tapped into the wires at the VSS and ran new wires into the cars comoputer. Problem solved! I must have a rotten wire in the stock harness.