Thats what it sounds like. Diagnostics is a step by step procedure. Check the easy things and most common problems first. There is a saying in my line of work when it comes to diagnoseing problems. KISS it. Keep- It- Simple- the last S I will keep to myself.
The decoder is making sounds when you have control. The track is somewhat clean because you were running other locos at the same time. You said it ran good the week before so it sounds to me that either a contact problem or bad conection in the plug.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
So you think that it is a connection problem and not the decoder?
Check those little wipers behind the drivers and also the ones on the tender trucks. Make shure they have real good contact and spring back. Then check the plug between tender and loco. Unplug and look for bent pin and blug it back firmly.
It could be several problems. It could be poor continuity in the tracks (joiners not tight, dirty tire surface on the rail heads, weak signal due to insufficient feed) or faulty wipers, dirty wipers or wheels, misaligned wipers, improperly seated connection between tender and locomotive (they do wiggle loose, and more quickly unless you firmly press them into the socket the first time...even then some of them are poorly designed and will come loose due to the wires flexing on curves and over turnouts). Your hand-held throttle, if you are using one, may have an intermittent wire contact along its length or at the press-in connector. Decoder, itself, may be loose.
You have to begin a series of eliminations, but often they begin with diagnosis and observation. The next time the engine stops, press the joiners on either side of it and see what happens. If it moves, you'll know what the problem is. Inspect the wipers and the connector between tender and engine....and so on.
A week ago I bought a Bachmann Spectrum K4 with sound and DCC. When I brought it home and ran it on my DCC layout it sometimes would just stop. I assigned it a 4 digit locomotive adress and ran it fine for the rest of the day. A few days later I came back and put it on the layout and typed in the adress. At first it wouldn't respond and after a few minutes got it to respond. Then after about a minute, it just stopped running and wouldn't respond to any sound command. I tried to reprogram it but it wouldn't accept any new adress. Sometimes only the sound would work and it wouldn't move, and othertimes it would move but it wouldn't respond to a sound command. Everytime I would get control of the locomotive it would run for a short time and then stop and it wouldn't move. Does anybody have any suggestions or help?