I have a 2001 Ford Escape with a 3.0L V-6. i just did a complete engine rebuild(vehicle had 170,000 miles) after 500 miles the "check engine" light came on. The only code was P0420, i cleared the code, another 100 miles or so and the codes was back. I replaced the rear HEGO on the back(rear) bank of the engine. My question is: Is the rear of the engine bank #1 or is it hte front?