2003 Jeep Liberty

I would start with having the blender door checked. It's located near the heater core and determines if you get AC or heat into the vehicle. It is actuated by vacuum, so there is a chance you have a vacuum leak.

The car's computer receives signals from sensors. If there is a problem, it set a code in the computer and the light turns off. What you need to do then is have the computer scanned to know what code is set and where the problem is coming from. As far as the blender door, it wouldn't set the light.

Most nationally recognized parts stores wll scan the computer for free and tell you. If the light is on, that is what I would recommend. Let me know what you find.

Did he reset the light after you replaced the cap? If he did and the light came on again, the gas cap isn't the problem. He most likely got an EVAP code and it could be a cap or several other things. If that is the case, take the car to a shop and ask them to fog the EVAP system. What happens is you most likely have a leak somewhere in the system. You could look for days and not find it. If the system is fogged, they fill it with fog, and wherever the leak is, the fog will leak out and they can identify the leak.

If he didn't reset the light, it needs to be done. Once the light is out, it may stay out because the cap may have been the problem. If it comes back on again, then do what I mentioned above unless he said something other than an EVAP code was found.

Let me know what he said, and if you have other questions.

Take care,
Joe