Did you use some type of memory saver while the battery was disconnected? GM is one of the three worst manufacturers at designing in tricks that require trips to the dealer after just disconnecting the battery or letting it run dead. Usually though if the engine starts, no computers should be locked up and everything should work, however, the instrument cluster is now an entire computer module itself. Since some gauges are apparently working, look at your speedometer to see if the needle is on the wrong side of a little peg that sets its position at "0 mph". These are not the reliable and trouble-free spring-loaded gauges we had in the past. The needle is placed at the desired position by pulsing the coils inside a "stepper" motor. When you reconnected the battery, a voltage surge could have caused the needles to jump momentarily, and if one jumps more than half way around the dial, the next time you turn on the ignition switch the computer magnetically runs that one back to "0". It always takes the shortest way to get there and that is to go clockwise, but then it gets stuck behind that pin.
If that looks like what has happened, there's three ways to correct it. The easiest is to just go out and drive it and hit a speed that is more than half scale. You need to hit the speed that would normally have that needle pointing exactly away from that pin, then a little faster. The computer is constantly setting the needle's position and once getting to it the shortest way is counterclockwise, the needle will bounce there, then follow the speed back down like normal.
The second way to return the needles is to connect a scanner and run the gauge test. That will run all of them to 1/4, 1/2, 3/4, and full scale, then back down. Once full scale is reached, the speedometer needle will come back down with the rest of them like normal. Not all aftermarket scanners have that capability, but a lot of independent shops have the same scanners the dealers use.
The third and most time-consuming way to fix this is to disassemble the front of the cluster and push the needles back down.
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Thursday, November 1st, 2012 AT 11:39 PM