will a defected speedometer cause the odometer on a 2004 chevy truck not to work. Its digital

of course same thing they work together .. .most likely a sensor down on the trans

It depends on whats causing the speedometer not to work. If it is your speed sensor then yes the odometer will also not work. If it is your gauge cluster then you will need to have it replaced. Legally if you replace the cluster the mileage needs to match the old one (should not be replaced with a truck with lower miles and not corrected). Some vehicles the mileage is retained in the ECU vs the cluster to prevent fraud.

Take truck to local dealer there may be a recall on this problem they did recall 2004 instrument clusters on sierra and silverado. To answer your question they will affect each other