My speedometer don't do a sweep when i put power on should it

could be the computer trying to tell you an error code.

CPU Unit may be faulty, will not give you true readings .

Circuit/System Verification
Important: If the suspect gage is the speedometer, the drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear.

1. Ignition ON, with the scan tool, perform the IPC Gage Sweep Test in the IPC Output Controls. Verify that all gage dials move from minimum to the maximum value and back to the gage minimum value.
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If the gage does not perform the IPC Gage Sweep Test, replace the IPC.

2. Start the engine, with the vehicle drive wheels raised and place the transmission in drive or first gear. Verify that the speedometer value matches the scan tool Vehicle Speed parameter in the ECM/PCM Engine Data List.

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If the speedometer is incorrect, test or replace the IPC.

Speed sensor is mounted on gearbox and counts the final drive gear teeth to compute bike speed. These are a sealed unit and do fail. Three wires, one has 5 volts, one is ground and the other is signal out. By using a signal generator square wave out, you can check the speedometer. Sweep the output from 10Hz upwards and speedo should sweep. Check at plug where sensor goes.

Dash board or gages

Have a shop sweep the guages with a scanner that has bi-directional controls for the application. If the speedo still rests at 100 after the sweep then you will need a new cluster. Or have the stepper motor rebuilt, its just cheaper to replace after you add in the labor. This is a very common problem with GM products.

trry this link
www.repairmanualclub.com

Sounds like a short in the cluster. You maybe able to recalibtrate it, but not likely. To recalibrate, Hold the trip buttons in, turn the key to the on position, wait for the gauges to start sweeping, or the odometer will display a fault code for you, release the button and see what happens.

sit in the drivers seat close the door. with the key off hold the trip odometer button in then while holding the button in turn the key on. if done correctly this will put the MIC (mechanical instrument cluster) into a self test. if the speedometer does not move like the rest of the gauges during this test the MIC must be replaced. if the speedometer does move it is likely your problem will be fixed, however, if the speedometer does move but it does not start working properly then further diagnostic will be needed.