P0174 p0491 p0492 code info - AudiWorld Forums

A8 / S8 (D2 Platform) Discussion Discussion forum for the D2 Audi A8 and S8 produced from 1994-2002

P0174 p0491 p0492 code info

 
Old 02-06-2019, 09:57 AM
  #1  
AudiWorld Newcomer
Thread Starter
 
Join Date: Feb 2019
Posts: 3
Default 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.
sponerdiner taylor is offline  
Old 02-07-2019, 10:59 AM
  #2  
AudiWorld Senior Member
 
Join Date: Oct 2005
Posts: 890
Default

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.
jfrahm is offline  
Old 02-07-2019, 01:46 PM
  #3  
AudiWorld Newcomer
Thread Starter
 
Join Date: Feb 2019
Posts: 3
Default Thanks

Originally Posted by jfrahm View Post
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.
I'm trying to figure out where to start. I checked this morning on cold start and didn't hear siap running so I'm gonna start there. Then vacuum lines. Thank you for replying.
sponerdiner taylor is offline  
Old 02-08-2019, 04:50 AM
  #4  
AudiWorld Senior Member
 
Join Date: Oct 2005
Posts: 890
Default

OK if you need more help maybe tell us what car you have.
jfrahm is offline  
Old 02-08-2019, 08:56 AM
  #5  
AudiWorld Member
 
SC_09iduA's Avatar
 
Join Date: Nov 2009
Location: MTns
Posts: 139
Default

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...
SC_09iduA is offline  
Old 02-08-2019, 09:37 AM
  #6  
AudiWorld Newcomer
Thread Starter
 
Join Date: Feb 2019
Posts: 3
Default 2001 a8 4.2

Originally Posted by jfrahm View Post
OK if you need more help maybe tell us what car you have.
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.
sponerdiner taylor is offline  
Old 02-08-2019, 12:53 PM
  #7  
AudiWorld Senior Member
 
Join Date: Oct 2005
Posts: 890
Default

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.
jfrahm is offline  
Old 02-08-2019, 01:35 PM
  #8  
AudiWorld Senior Member
 
Join Date: Jan 2004
Posts: 607
Default

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

Last edited by BrianC72gt; 02-08-2019 at 01:55 PM.
BrianC72gt is offline  
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
compassluxor
A8 / S8 (D2 Platform) Discussion
6
05-24-2013 01:12 PM
Zuds41
A6 / S6 (C5 Platform) Discussion
2
07-23-2011 01:20 AM
tdhixon
2.7T V6 Discussion
3
11-13-2008 02:21 PM
DashingMax
A6 / S6 (C5 Platform) Discussion
10
06-22-2004 09:04 PM


Thread Tools
Search this Thread
Quick Reply: P0174 p0491 p0492 code info


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: