2004 GMC Envoy speedometer

You need to scan for "B" codes with a tool capable of reading them, but it should show this code.
DTC B0540: SPEEDOMETER CIRCUIT Circuit Description The IPC monitors the vehicle speed signal to determine the speedometer position. If the IPC determines the vehicle speed signal voltage is out of the normal operating range, a DTC will set. Conditions for Running the DTC à   The vehicle speed is more than 10 km/h (6 mph). à   The ignition voltage is between 9.0 volts and 18.0 volts. Conditions for Setting the DTC à   The IPC detects that the commanded state of the output driver and the actual state of the control circuit do not match. à   The condition above must be present for a minimum of 5 seconds. Action Taken When the DTC Sets à   The IPC stores a DTC B0540 in memory. à   The speedometer defaults to 0 km/h (0 mph). à   No driver warning message will be displayed for this DTC. Conditions for Clearing the DTC à   The history DTC clears after 100 malfunction free warm-up cycles. à   The DTC becomes history when the conditions for setting the DTC are no longer present. à   The IPC receives the clear code command from the scan tool.
You can also check these four ground points, clean em up with sandpaper and reattach.