My mother'* 1998 Bonneville SE had a strange problem today. The speedometer is way off. When you drive 20 mph it will show 40 and the faster you drive it gtes even more outrageous. At about 40 mph the speedo says about 70! I also noticed the system isn't charging at all and the Check Engine light came on. Any ideas or has anyone ever encountered this? Could these things be related?

Seems like alot of electrical gremlins here are caused by corrosion on the battery terminals. Pull them apart, clean them and put them back togather. Check the grounds for corrosion also. Then check the connections at the alternator, make sure that they are tight and clean. If all is well, check the alternator. If you cannot test it yourself, Auto Zone and many other parts stores will check them for free. Probably a good time to have the battery load tested as well.

Hope this will fix your problems.

Probably has something to do with the check engine light..have it checked out. If the charging system died and the voltage is low..all sorts of crazy things have been known to happen.

The battery is a new Delco installed a few weeks ago. I checked all the connections and everything is tight and clean. We are taking it in tomorrow to check everything out. I sure hope the whacky speedo is related to the charging system. I was thinking maybe it had something to do with the transmission. I sure hope not. The car only has 56,000 miles on it but it apparently sat for awhile. We purchased it in late February. I will let you all know what they find. Thanks for the feedback. I love this forum!

I'm thinking a wheel speed sensor....

You will end up being wrong... the VSS which feeds the PCM and then the speedo is located on the transmission. WSS only feed the ABS/TC.

When you say all connections are clean and tight...did you look UNDER the rubber boots on the cable ends?

After taking the car in to be looked at, the problem was a bad alternator. The lack of any charge caused the speedo to act up since it is electronically controlled.

The check engine light had nothing to do with the alternator. That was caused by a cracked hose on the emissions system evaporator line or something to that effect. All is well now. Thanks for everyone'* input.

We are here to help... The more information you give us..the better we can diagnose the issues.

The battery must have been getting low for the gauges to start acting that bad.