P0174 p0491 p0492 code info
 

Hey I have questions regarding the codes I'm getting. Was curious if the p0174 because of the saip codes or vice versa? Also not sure which o2 I should be going after. I know its bank 2 but pre cat or after cat? Thanks in advance for any help.

Start by googling the codes. None of those are O2 sensor codes? Or do you think the bank 2 O2 sensor is showing lean because it is faulty (this is unlikely)? However the front O2 is for tuning AF, the rear is for catalytic converter efficiency.
The lean code may be due to a big vacuum leak from rotted out vacuum lines to the SAI valves on the back of the engine, at least I found on my D2 A8 these hoses were bad.

Thanks
 

OK if you need more help maybe tell us what car you have.

Also, it's been noted before that the first place to check needs to be the fuses/relay for the SAI...replace the hoses and keep rocking them or delete them and code the CEL out...they are a PITA to be honest...once they start acting up, you'll be chasing the forever...

2001 a8 4.2
 

2001 a8 4.2 also unrelated to the cel the car will randomly start and stall due to the immobilizer. Dise the fob battery have anything to do with the immobilizer? I serched the a8 d2 forum and not much info except for how to disable it. Again thanks for all the help.

No the fob battery is for the remote lock/unlock.
Flaking Immo is usually improved by disconnecting the gauge cluster connections and then re-connecting them. This worked for me. Some say it's "rebooting" the cluster that does it by disconnecting it from the power and bus.
These instructions on installing gauge rings show how to partially remove and disconnect the cluster:
audipages Installing Dash Rings in the Audi A8/S8

You just need to get the cluster out enough to reach behind and disconnect the harnesses.

Secondary Air Injection codes are usually caused from breaks in the vacuum hose running all over the engine bay used for triggering solenoids. Here is the procedure:

audipages 40 Valve Vacuum Hose Replacement

Basically, start at the back of the engine, passenger side (for rhd cars), and work clockwise around the engine chasing/replacing the frayed/broken braided vacuum hose.

Hose: https://www.jbugs.com/product/N203531.html

Thank you to PaulW for hosting that site.

Regards,

Brian

Saip fuse?
 

not sure where the fuse is for the saip. Im only getting 3.5 volts to the relay. I jump out the relay and pump turns on.