My 96 Bonneville SE has a speedometer that reads between 10 and 15 mph above what the car is actually doing. A Google search turned up quite a few 1996s with the same problem. Most posts I've read say they replaced the VSS but still had problems. I've got the original wheels/rims and the stock suggested tire size so it'* not a wheel/tire size issue that'* throwing things off.

As an added bonus, I've also seen that Rock Auto has an ABS wheel speed sensor and coincidentally, my ABS Brake indicator light is on (and stays on) on the dash.

Car accelerates and shifts smoothly with no issues. The only problems are the speed being off and the ABS light being on.

Where should I start troubleshooting?

ABS light is best to scan and see which WSS is not reading properly, then replace that hub/bearing.

On the speedo reading fast. This is read solely from the VSS sensor on the transmission and determined as 4000 pulses per mile. It'* very odd that the speedo in the cluster could be running faster than the car. Best to scan the pcm as well for mph to determine if the speed matches between the pcm and cluster. If they do, it would appear that the VSS reluctor or diff may be incorrect. Maybe a bad VSS or the ground for it.

Or would metal shavings have an effect Bill?

I've pulled a good number of VSS full of shavings with mixed results. Usually glitching/twitching speedo, not higher though.

Bonnie'* been running well so I haven't been playing with it for a bit but it'* time to roll up my sleeves and clean up some of the lingering issues. Like the new site by the way.

Couple of questions...you mention "scan" in a couple of places. Just want to make sure I'm understanding this correctly. I assume you mean scan with a scan tool that reads live engine data. Would something like the Equus 3160 Innova work or do I need something a bit more substantial? As for scanning the WSS, can I do that with a voltmeter (and if so, what am I looking for) or would the same tool I use for the pcm scan work?

And just to confirm...the VSS is on the lower back of the engine? I haven't gone looking yet but is it easy to recognize? My Hayne'* manual doesn't have a picture.

Not sure if that particular scanner does live data view.You'll have to check the mfg'* website to make sure.

Yes, you can use a multimeter to check wss. Just use the lowest AC scale, and disconnect the connector at each wheel. Spin tire and watch for readings, jumping voltage etc.

Your VSS is located on the differential housing on your transmission....

The speedometer used on most GM vehicles are of the Air-Core design. This is a moving needle operated by a magnetic coil. Because there is no direct mechanical linkage, there is some variation in accuracy that cannot be eliminated.

Digital readout devices, such as some speedometer displays and Head-Up Displays (HUD), are direct readouts of the Vehicle Speed Sensor (VSS) and their accuracy is much greater. Tire size, tread life and inflation may cause some variation in the readings. In addition, the Tech 2(R) reads the VSS directly and is quite accurate.