Polar express battery powered wood engine works and then doesn't

Sounds like a track connection not completely together. Put a meter on various points on the track to find where it is not completing the circuit.

these are all basically at the same time in sequence,

1. test batteries, need at least 75-80% power for train to operate at all. will be very weak but should operate. or use known good batteries.

2. next are the battery contacts. a lot of time the positive contact gets bent so far it either makes no or very weak contact, simply bend it back out very carefully to make better contact and clean it with a little rubbing alcohol of nail polish remover and a q-tip.
3. next would be the switch for continuity and then loose or broken wire.
after that you can email me for further help.
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IfIam correct, the basic Polar Express came with just a whistle. There is an optional coal tender that has a better sound system in it...Whistle bell and steam sound also try reversing the power wires at the transformer or track

The instructions are sometimes a bit vague: for example, once switched on the train needs to sit and charge before it runs, but that is not very evident from the instructions and many folks spent some frustrating minutes wondering why the train wouldn't move.

There are more than just one Polar Express set. What's the set number?

Replace all the batteries, then keep the remote close to the
train. if it's too far away, it will shut down.

No power to the transformer or to the track?
If not to the track, make sure you have the correct wire connections made from the transformer to track.
If no power to the transformer from the wall plug,
sounds like the cord needs replacement.

I rewired my train this weekend..it now works on my outdoor setup....I found that the circuit board inside the engine had a blown capacitor and the power transitor was fried. I by passed the engine board found that it only would run backwards....went into the tender and taped into the power from tack bypassing the rectifer... By the way the engine does not start up when one uses the remote...there is a 20 second delay before starting

Search the Internet. Also contact the manufacturer, they may be able to email you a PDF file containing the instructions.

There is a small screw hole on top of the train, down inside what looks to be the smoke stack.  Then insert 2 AAAs!