So I have an XL80 and am having problems getting it to light. I am getting a diagnostic code of 9 flashes. Which is check ignition. Will the gas valve not work if this diagnostic code is happening? I tried to light it with a fireplace lighter but it is not lighting. I either think the valve is bad that controls the gas being sent to the burners or it is not working because of the diagnostic code that I am receiving.

While I am not familiar with the Trane furnace, I'd take a look at the "hot surface ignitor". This part should be easy to test and replace. Get it at a local appliance parts dealer.

Best of luck,
WallyH