Engine lights

[wch]

Hi, I have 4 bachmann enines with DCC on board. I'v had them for a year or so.I'm in the process of building my layout. I'v been running theengines for almost a year with DC power. For the last month or so the engine lights come on when their first powered up, but then go out within a minute of operations. I just switched to DCC and the same issue exists. Is this a issue with the lights or some other issue. It just seemed strange that they all developed this issue around the same time even thought they don't all have the same run time.