Ok so I have the code p0131 that causes a CEL every now and then. Code says it's the bank 1 sensor 1. I have been unable to find somewhere that says exactly which location this is. Is this in the front by the radiator or behind the engine between the engine and firewall? If someone can please provide this answer it would be much appreciated. I don't want to accidentally take out the front sensor and find out I need to replace the one by the firewall.