Check Engine Light

I'm no master mechanic. For some reason every time I tow my boat, the check engine light comes on in my tow rig. It's a 2003 GMC Denali, 102K miles. I've never had any problems with it, wondering it this is a prelude to issues coming my way?

I would take a stab at it being a transmission issue with the weight of the boat. They have soft codes programmed in and if something happens where it may cause it to slip it will trip this code and cause the light to come on. Do you use the Tow/Haul mode when pulling the boat? Another thing you may do if you dont have the Tow/Haul mode button on the gear shift is to drop it out of Overdrive and into 3rd and you probably wont have any more "Lights" but you wont be able to drive/tow as fast. Any problems with the light when not towing?

Sounds like a post converter O2 sensor code. When towing, especially up hills, the exhaust gets extra hot and the converter gets a little overloaded and it's efficiency drops. At this point, the post converter O2 goes "lean", because the converter was not able to convert the remaining oxygen to CO2.

I Think the post converter i Had an 09 that did the same thing

sorry i had a 99 not an 09.

I use the tow/haul mode when towing. The light will not go out right away when I unhook. Usually takes about 10-15 miles for it to go out, then I don't see it again until towing.

I'd bet there are service codes that will be logged. You can try the ODBC scanner from your local auto parts store. But sometimes the chassis codes can only be accessed by the dealership service dept.

If it were me I would just hook the boat up and pull it until the light came on and then have the code read at an automotive parts store or dealership. Most places wont charge you just to have it checked and then you will know. Those lights are so sensitive that if you dont put the gas cap on tight it will come on.

Thanks guys for all the input