I just picked up an 03 LS with every option.This thing has been a challange to say the least.I do like the car and I am hopeful I can fix the issues and enjoy the car.

So far I have had the throttle stick and just about get me killed.After remove and clean of throttle body,new TPS,new cables it turned out to be a defective pedal asm.The pedals are stocked at all my local dealers so it must be an issue of some kind and it only cost $40

Over heating was a stuck thermostat not to bad to fix.Flushed the system while I was in there as well.

Door locks inop was just a fray wire under dash a pain to find but easy fix.

I am left with 2 issues
Trunk is leaking water and the radio says LOC,I did try the hold 1 and 4 buttons but it never shows any number.On my radio you cant hold 2 and 3
so I guess the radio is toast.The truck seal I replaced so it must need the latch adjusted.

Any input for my last 2 issues?I would be glad for any help.

LOC is displayed when the VIN expected by the radio isn't what is being transmitted by other modules in vehicle. Is it possible you have a radio from another vehicle installed? I think only a dealer can fix that because they would have to force the radio to relearn a new VIN.

Do you have owner manual for vehicle?

https://www.mygmlink.com/pdf/go2content/manual/US/en/chevrolet/2003malibu.pdf

A friend of mine with an '02 had a bad tail light gasket leaking water in the trunk-might check that.

Not in my Malibu, but my Yukon XL gives me a LOC about once every 3 months.

Well the throttle sticking turns out to be the pedal asm its self.New gas and brake pedal unit was instock at local dealer they had 9 of them.Radio was locked due to the vin not matching.It was a junk yard unit so I just put in an after market cd with sirius.Have not gotten to the water leak yet.