It is locked in a speed control on mode. You need to unlock it. Read below and give it a go and you should be OK. Before doing this, reprogram your engine.
Transformer operations Your locomotive’s Odyssey™ System speed control You can lock your locomotive into speed control mode (ideal for low speed operation) so it will automatically compensate for grades, or to simply maintain a specific speed setting. To turn on the speed control, get your locomotive moving at the desired speed, in forward or reverse. Let it run at the desired speed for at least 5 seconds. Press and hold the horn/whistle button for 2-3 seconds as you increase the throttle by at least 3 volts. Your locomotive will accelerate briefly, then will return to your set speed once you release the horn/whistle button. As long as the throttle position is maintained at a higher setting than the initial level, your locomotive will maintain a constant speed. If the throttle is turned below the original level, your locomotive will slow down due to the available voltage decrease below the “set” level. To check if the speed control setting has been “accepted,” turn up the throttle. You will see the lights brighten, but the speed will remain constant. For best results, adjust the track voltage about 3-4 volts above the “set” point. This will provide enough spare voltage to compensate for uphill grades, etc., but will prevent excessive voltage to the lamps and smoke unit. (In conventional mode, these operate at track voltage, and excessive voltage may lead to premature bulb burn-out.) • If you wish to change the speed control setting, you must deactivate the speed control, then reactivate at the new setting. To turn speed control off, get your locomotive into neutral for at least 5 seconds. Press the horn/whistle button for 2-3 seconds while lowering the throttle voltage to 1/4 of full power or at least three volts. Do not turn the throttle off or speed control may not deactivate. This can be difficult if you have established a low speed control setting. Once you are in neutral, you can increase the track voltage before pressing the horn/whistle button and lowering the voltage. This will give you more “room” to lower the voltage. (The speed control deactivates when it sees a 3 volt change with the horn/whistle button pressed, regardless of initial voltage level.) Note! Speed control settings are retained in memory even if power is turned off. They will remain present until deactivate
