1990 Chevrolet 1500 Pickup Q&A

1990 Chevrolet 1500 Pickup Question: check engine soon light stays on when pulling a trailer

After I put a load in my trailor I go approx. 15 miles then the "service engine soon" light comes on steady and stays on. I turn off the engine unload my load, I start the truck up the light is out,It does it everytime. When I go a distance with the trailor empty the light does not come on at all. -
Answer 1
Once the Check Engine Light has come on a code is stored in the computer it would be interesting to know what code is stored to see if it relevant and worth "fixing". -