One nice thing about the 99 is that the drive cycle for the engine control system has been simplified. This makes it much easier the do a repair, reset the monitor system, drive and see if the error occurs.
This version of the evap system on a 99 GLT still has the canister at the rear of the car near the fuel filter. Other cars have the canister in the space under the driver's side front fender. The purge valve is mounted on the radiator shroud. I decided to give the front of the system a once over. It is important to note that in the 99 version of the turbo charged engines the intake manifold is a different design than the 98 T5 cars that I also own. MOST important is to recognize that the MAIN vacuum line used for the EVAP system, Brake Booster, and possibly the turbo boot valve ALL use a single line that comes off a nipple that is right on the top of the manifold near the fuel line in the middle of the manifold. There is NO vacuum tree. Fortunately this hose if visible and a strong flash light gives a good view and the line. There I saw a dried out line that looked cracked. Closer inspection showed that it was.
There is a short run of "3/8" rubber line that goes behind the manifold and comes out on the drivers side of the manifold as 5/8" inch (all measurements are approximations) into a T fitting that has a medium diameter hoses and check valves.
How does the diameter change? There is an inline adapter. The attached photo came from a different article on this site related to poor idle performance but shows the adapter and the same split down the length of the line! On my vehicle this is NOT a check valve. It is just an adapter for two different size lines.
My hose had the exact same cracks running along the top and bottom of the hose for the same length. Since the car had been running well and had no codes I can only guess that the hose was collapsing along the length as vacuum was applied until it failed completely and opened up. The system lost vacuum, triggering a "gross leak" code. I was not able to find any vacuum lines at a local parts store that worked. Fortunately I collect stuff like this to help bail me out of situations like this one. I found some transmission coolant line for the wider hose and some vacuum line for the thinner section to rebuild this line. I used screw clamps at the adapter and just attached the ends of the line to the T adapter and the manifold nipple.
Driving the car with the repaired line has cured the P0455 code. All monitors are in the ready condition.
Boost response seems to be better.
Ever since I purchased this car with only 59000 miles on it the brakes have not been as good as on my other to 1998 s/v 70s.
Since I replaced this line the brake pedal feel had improved. I had previously bled the system and did other brake work but the feel was always different with more travel before the brakes grabbed. Now it is better and more like the other cars.
Hope this helps others with the same dreaded P0455 code.
