The speedometer quit working in the Buick Skylark. I replaced it, but now it works when the car is in reverse and does not work with the car goes forward. Can anyone tell me where I messed up? This is a digital speedometer w/odometer.

 

What do you mean by quit working? Does it always register zero unless it's in reverse? Is it blank / dead unless you're in reverse?

 

This is what has happened. The vehicle is a 1988 Buick Skylark, 2.5 liter, 4 cyl engine, 3 speed transmission w/torque converter lockup. Replaced the speed sensor because it quit working. Did not register at all. Replaced it with one that looks identical. Now it registers speed when the vehicle is in reverse, but doesn't register at all going forward. Hope this is the information you needed.

 

When it doesn't register the speed, is the speedometer reading 0 (zero)? Or is it just blank, as if the key was off?

 

Check to see if the computer has a code for a bad speed sensor.
If you have cruise control, see if it works, not on just a flat surface, but check to see if it can maintain a speed when going up a hill. This should be done at a speed of 40MPH or more such as on a highway. That may help to determine if there is a fault with the speed sensor circuit or the digital speedometer.

 

This is a 1988 Buick Skylark with 660,000 miles on it. It has cruise control on it, but it has not worked in a long time. It is not a digital speedometer so when going forward, the needle sits at 0. In reverse, it registers the mph.

I really appreciate all the help you all are giving. Thanks a lot.

 

I'm confused. Digital or not?
Is the odometer correct?

 

If I recall this is a spedo with a pointer for the speed and a digital odometer.

 

Yes, this is a speedometer with a pointer and a regular odometer...does not light up or anything.

 

Thanks for clearing that up michael van and PatOba.

Any chance you could have installed something reversed, a connector or wires? Are you sure the speedometer you replaced was identical funtionally with the one you replaced? Eg: Was it crossed referenced to fit your car at a junkyard? Wondering if the speedometer is an exact replacement for the original.

Just out of curiosity, have you tried using the cruise control since replacing the speed sensor?

 

Everything seems to be hooked up correctly. I was told it could be the VSS Buffer causing the problem. Any idea where the buffer might be located on the 1988 Buick Skylark? I have looked behind the glove box where someone said check. It it is there, it is hidden really well.

 

...that the buffer/amplifier is located in the engine controller. it was a separate piece used mostly on cars with mechanical cable driven speedos. at any rate...the buffer would bolt on to the back of the speedo assy right next to where the cable plugs on. yours doesn't have a cable, it's electronic...so...try removing the speed sensor and have someone watch the dash. spin the speedo gear in both directions while they watch for a speed indication...i'd be surprised if you only get a reading in one direction doing this test...as the speed senor generates an ac signal and it makes no difference electrically which direction it turns.

bottom line...if you get a speed indication when you do this...the problem is how the drive and driven gears are meshing in the tail end of the trans. perhaps the plastic driven gear is worn...

 

So, the VSS Buffer is not a necessary part of the 1988 Buick Skylark (without a cable driven speedometer)? If it turns out to be worn gears, can they be fixed or is another speedometer and speed sensor going to be needed?

 

...the vss buffer is built into the ECM...it can't be the problem if you get a speed indication in reverse...it almost has to be something else. that's why i suggested spinning the VSS by hand. if the gear is worn, it's replaceable. i can't imagine that the drive gear is messd up...it's metal and pressed onto the final drive carrier inside the trans. likewise, i can't see that speedo being the problem...it doesn't make sense that it would display a speed in reverse but not forward. the electrical signal produced by the VSS is a simple one and the speedo head either reads it or it doesn't.