While there are many different symptoms of transmission problems in a Ford Explorer, one frequently reported symptom is the illumination of the "check engine" light on the instrument panel. While the light says to check the engine, the sensors throughout the power-train constantly check the condition of the engine, transmission and, in some cases, the anti-lock brakes.
The smell of burning transmission fluid indicates that the transmission is overheating. Ideally, the fluid is a bright red on the automatic transmission dipstick. If it is brown, the transmission is overheating. One common cause of the overheating problem is low transmission fluid, normally caused by leaks. Owners need to refill using the vehicle manufacturer's recommended fluid in order to prevent overheating. If the vehicle continues to leak, repairing it is necessary to prevent further damage.
If the Explorer's transmission is noisy while in neutral, it is likely suffering from excess wear. HowStuffWorks indicates such noises are indicators of worn bearings, a worn reverse idler gear and possibly worn gear teeth.
Under normal operating conditions, the Explorer's automatic transmission shifts from one gear to the next in a way that is almost undetectable. However, if the Ford starts to shift roughly, there is likely a developing problem with the transmission. HowStuffWorks recommends taking it to a mechanic for a check.