Engine light and AT light
 

My engine light was on all day yesterday and for about a minute, the AT light was on. During the time the AT light was on the car wouldn't shift into 4th gear - it didn't cause any problems.

The car drove fine all day and by the next morning, the engine light was off.

Took it to one mechanic I trust - he said they don't do transmissions, but he said it could be bad solenoids ?

Went to the Mazda dealer and they said it would cost $150 to diagnose, but it would be better if the engine light was still on. They suggested that it might be the speed sensor.

Anyways, the car is driving fine now and drove it all day with no warning lights.

Does anyone think this could be the beginning of a transmission problem or another issue ?

The car is a 2005 Mazda 3 sedan with 225,000 kms (140,000 miles).

Thanks.