My 1941 Lionel train stops getting enough power to run all the way around the track. Voltmeter says 15 volts around all track and transformer says 15 volts. How do I test engine?

All the parts have worked for years in the same configuration. Usually I just clean the track with emery paper. Did not work this time. All the parts have worked for years in the same configuration. Usually I just clean the track with emery paper. Did not work this time.

It may be that you have dirt build up on the wheels or your motor brushes are worn down or that graphite from the brushes is packed into the commutator slots creating a high resistance short circuit. Check the wheels first. Use a small piece of wood to scrape off any hard, built up dirt from the wheels and contact rollers. If that doesn't help, take the engine shell off and unscrew the brush plate. Replace the brushes if they are too worn. Clean out the commutator slots carefully with a pointed wooden dowel. If you don't want to do the repair then take the engine to a Lionel service center. My guess is that you have worn out brushes. It may be that you have dirt build up on the wheels or your motor brushes are worn down or that graphite from the brushes is packed into the commutator slots creating a high resistance short circuit. Check the wheels first. Use a small piece of wood to scrape off any hard, built up dirt from the wheels and contact rollers. If that doesn't help, take the engine shell off and unscrew the brush plate. Replace the brushes if they are too worn. Clean out the commutator slots carefully with a pointed wooden dowel. If you don't want to do the repair then take the engine to a Lionel service center. My guess is that you have worn out brushes.