no gas tank pressure

hello. my 2004 s10 blazer 4.3 ltr 4x4 with 23000 miles on doesn,t have any pressure in the gas tank yet i don,t have any codes.the only indication of a problem is when testing with obd2 tester i have a yellow light that indicates test pending. however it has been that way for about a month.my gas cap seems fine. i would appreciate any input you might have in solving this problem.also does anyone know where i can get a diagram of the EVAP system for this blazer? ty malamar

No CEL? Don't worry about it. All it means is the conditions to run the test haven't been met yet. Do you only take short trips, do you leave the tank full or empty, do you not drive on the highway at a somewhat steady speed? All the right conditions must be met before the test will run. Don't worry about it, yet.

thank you for your reply. you are right, i make a lot of short trips.but i keep the gas tank at least 1/2 full all the time.so i will let well enought alone. again thank you...melamar

hello. my 2004 s10 blazer 4.3 ltr 4x4 with 23000 miles on doesn,t have any pressure in the gas tank yet i don,t have any codes.the only indication of a problem is when testing with obd2 tester i have a yellow light that indicates test pending. however it has been that way for about a month.my gas cap seems fine. i would appreciate any input you might have in solving this problem.also does anyone know where i can get a diagram of the EVAP system for this blazer? ty malamar

They are made to run under vacuum not pressure.

If the yellow light is on it is because of a code.
Check code no and clear codes and see what it does.
If a code post back code no.