Speedo doesnt work after battery swap?

[kev2809]

2002 ext cab sierra, 4.8 auto, 97k miles

Was working perfectly fine, battery quit on me after work on friday. went down and got a duralast battery from autozone and now the speedo doesnt work. truck turns on and runs fine, all other gauges work. as soon i put the battery in, i jumped in to start it up and i noticed it was sitting all the way on the other side. turned it on and took it around the block and nothing....

anyone know why this would happen?

[kev2809]

guess ill post to my own answer. i got in the truck and hit about 40 mph and it started working again. i think this might be an early sign that my cluster is goin out (from i have been reading, its a common problem)

[bigrusty]

It could just be the way it was sitting on the other side. The stepper motors are zero contact, relying purely on magnetic fields made with coils, and the position changes depending on an input voltage, with each position being specific to a voltage. As your speed changes, the voltage changes and the motor takes the shortest path to the next position. When your needle was on the other side, it didn't go to your actual speed until later because the shortest path to your actual speed was to continue around clockwise but that was impossible because it was being stopped by the plastic rest, so it just sat there until the shortest path became "possible".

If you turn you key to the "on" position really quickly and then off again without cranking the car, you might notice that your gauges jump a bit or move. When your battery died it could have made the odometer jump to the other side and get stuck.