The codes are for the secondary air injection systems and the 491 and 492 are for banks 1 and 2. There are a few things to inspect when this code comes up. The first is to inspect the system checking for a proper seal. Check the connection pipes and hoses between the Secondary Air System, (AIR), pump motor and the combination valves for a proper seal. See FIG 162 for the pump location.
The solenoid for the system may be bad but you need a special tool to test it so if you go through all the suggestions I give you as it is something you may have to have a repair shop adress.
Then, you can check the fuse for the air system, see FIG 194 Position B, to see if it is okay. Another FIG 195, shows the position of fuse S234 which is in the number 34 position in the fuse box. I hope the included diagrams, (FIGs), help you to determine if there is anything you can do.
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Thursday, December 15th, 2011 AT 11:09 PM