Not sure, I just had a similar code reported with my Durametric (I can't remember the exact number sorry) and it seemed like the problem was just a loose gas cap. I looked up your error number in AllData for your 99 but it wasn't there (I only saw 40440 and 40441 I believe)
The book says it is for detecting leaks in the fuel tank ventilation system. And that there is a problem with a line or 1 or 2 valves.
Vapors from the fuel tank are collected in a cannister. When the car is running these vapors are sucked into the intake and burned. US law requires an onboard system to determine if there are leaks in the emission system. A vacuum is created in the tank and measured with a pressure sensor to determine if you have a bad line or valve(s) for the emission side of the tank. There is a valve to open the cannister and a valve to close the system so that vacuum can be built up.
So with that code the book says you are to check the lines and valves for leaks. Like when you forget to put the gas cap on and get a check engine light.
Linear Mode
