Interesting developments: P0492 and P0491 -- Request Tech Assistance

[JD S4]

Alright.. So for the last 6 months I've had a P0492 and P0491 codes on my B8 S4 (Secondary Air Injection - cold start).

So here is what has transpired:
I removed my supercharger to add an EPL pulley as well as change out (preventative) thermostat. I also added a Gen1.0 MercRacing Heat Exchanger during the process.
Upon first drive after reinstalling - I pulled a check engine light P0492 and P0491 for the SAI.
This was strange but I figured that during the install - I must have triggered something for the carbon buildup block flow and trigger the light.
So. I took the car to Audi for extended warranty cleaning of the SAI and they cleaned it under warranty. Picked the car up, CEL gone. 3 days later - it popped again.
So. I took it back. They took the car in again and the tech says the carbon/flow values are in spec. They spent the whole day on the phone with audi corporate tech and came back with this:
"Bad Combi Valve" - or EGR value. Quoted this not under warranty, $650 parts and labor.. Hmph.. Strange..
https://www.ecstuning.com/b-vemo-par...6e131101e~vmo/

There are left and right combi valves. But.. Now I'm suspicious AF.. Why? Because of the "binary" nature of this CEL. Car never pulled a CEL, then I pulled the blower for a mod and boom - CEL.. Did the EGR/Combi Valve go bad? Doubtful.

As of this morning - I am convinced (telling myself that) that I have a vacuum routing issue. This is where I need your help. I don't know the way the vacuum routing SHOULD be - but it's got to be that.

I created this thread a few months back with a bunch of pictures of my vacuum routing. Something must be wrong.. Can someone look at this thread (Audi Tech!?!?) and tell me where I am off?
https://www.audizine.com/forum/showt...ighlight=P0492

Also - after looking at this thread where the AZ'er had service work done and then pulled these codes and then found vacuuum lines weren't connected - I'm even more confident that this is the root of my error
https://www.audizine.com/forum/showt...ighlight=P0492

I may have a cracked hose or a hose routing issue. Please help!!! I'm going to tackle this thing - it would be much easier if someone way smarter than me just said "look bozo - you have these two vacuum lines switched around behind the throttle body" or in front of the blower...

There are lots of threads on this topic - with varying results. I know mine isnt an actual SAI carbon buildup since that is done - but I am skeptical on the EGR/Combi *actually* being bad since it was a binary before/after modification that it triggered. This leads me to believe that it's vacuum related somewhere.. I just don't know where..

[theweebabyseamus]

Hey bud, I haven't examined the pics yet but I do remember one hose goes back from the engine into the trans tunnel area. Also, have you tried pulling the blower again to see if there's a kink or something? This has happened to me.

Edit: let me take a look under the hood, I could swear youre missing an elec plug.

[whiped]

SAI Pump is behind the passenger fog then a hose goes up to either the stock airbox or to a small after market filter.

From the other side of the pump lines go out, up the front of the block, under the blower and down under the vacuum lines to the Combi valves.

1. Nut
􀁺 9 Nm
2. Bonded Rubber Bushing
3. Secondary Air Injection (AIR) Pump Motor -V101-
􀁺 Removing and installing, refer to Secondary Air Injection Pump Motor -V101-
􀁺 Attach the connector to the bracket
􀁺 Checking in Guided Functions using the vehicle diagnostic tester
4. O-ring
􀁺 Replace
5. Secondary Air Hose
6. Retaining Clip
7. O-ring
􀁺 Replace
8. Gasket
􀁺 Replace
9. Bolts
􀁺 9 Nm
10. Vacuum Hose
11. Right Secondary Air Injection (AIR) Combination Valve
􀁺 Checking, refer to SECONDARY AIR INJECTION COMBINATION VALVES, CHECKING
FOR FUNCTION AND LEAKS
􀁺 Removing and installing, refer to SECONDARY AIR INJECTION RIGHT COMBINATION
VALVE
12. Bolt
􀁺 9 Nm
13. Secondary Air Injection (AIR) Sensor 1 -G609-
􀁺 Removing and installing, refer to Secondary Air Injection Sensor 1 -G609-
14. O-ring
􀁺 Replace
15. Secondary Air Hose
16. Bolt
􀁺 9 Nm
17. Left Secondary Air Injection (AIR) Combination Valve
􀁺 Checking, refer to SECONDARY AIR INJECTION COMBINATION VALVES, CHECKING
FOR FUNCTION AND LEAKS
􀁺 Removing and installing, refer to SECONDARY AIR INJECTION LEFT COMBINATION
VALVE
18. Vacuum Hose
19. Bolts
􀁺 9 Nm
20. Gasket
􀁺 Replace
21. Bolt
􀁺 9 Nm
22. Bracket
􀁺 For the AIR hose
23. O-ring
􀁺 Replace
24. Secondary Air Hose
25. Bracket
􀁺 For AIR pump motor
26. Bolt
􀁺 9 Nm

You could pop the blower up and check all the lines if you really wanted to.

You can fairly easily test the Combi Valves both Left and Right side. If you think they are trying to pull a fast one have them show you in person.

You essentially blow into the PCV and confirm it is closed, then you manually presurize the valve to open it using a hand pump and confirm you can now blow through it.

Test should take all of 10 minutes.

[JD S4]

Thank you both - super helpful responses..

I'm trying to avoid pulling the blower *UNTIL* I have exhausted that it's not a simple vacuum or electrical miss where blower removal is not required.


Weemus - let me know if you see anything
Geoff - helpful diagram! I'll use that to trace lines. I am not suggesting that they are pulling a fast one. I know that they didn't actually remove the valve and test it - they just "diagnosed" it as it was clearly not the carbon. My assumption (perhaps incorrect) is that they are DX'ing it because of what they see (CEL after SAI clean) and not that they tracked it back and proved it was still bad..

Reality? If I paid them the $650 to replace - they would rip/replace the EGR and "fix" the vacuum issue during that replacement OR replace the EGR and say "whoops, that's not it" and have to diagnose it's something simple like a line or plug that I could have solved on my own with zero dollars..

Again - just a hunch based on HOW it happened.. The first time the CEL popped was immediately after blower removal. It is incredibly suspicious that an EGR or SAI carbon buildup popped "during" that and WAY more likely that MY dumbass messed something up! :-) I know myself.

Admittedly - I was hoping that during the SAI clean they would identify the vacuum/kink/electrical problem and fix it.. They did not.. So here we are (again).

[whiped]

If you messed up those vacuum lines in your first link they valves won't open which could cause an issue.

[quickglx]

You check the vacuum supply at the valves when they are active? Could be a throughput issue- solenoid or kinked vacuum line?

[JD S4]

You check the vacuum supply at the valves when they are active? Could be a throughput issue- solenoid or kinked vacuum line?

I don’t know what that means. Talk to me like I’m less smart than you did.

Thank you


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[bhvrdr]

I don’t know what that means. Talk to me like I’m less smart than you did.

Thank you


Sent from my

One of those plastic shits that all those hoses are hooked up to might be broke or the hoses themselves are bent up some making it hard for air to get through

[JD S4]

One of those plastic shits that all those hoses are hooked up to might be broke or the hoses themselves are bent up some making it hard for air to get through

Back behind the TB?


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[bhvrdr]

Yuppers

Back behind the TB?


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[JD S4]

Yuppers

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I’ll dig around back there. Anyone see anything that looks off in my pics?


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[bhvrdr]

I’ll dig around back there. Anyone see anything that looks off in my pics?


Sent from my

I looked at your connections and from up top they all look normal. Have you had the chance to pull the bumper and see how everything is working coming off of the secondary air pump

[Corradobrit]

Got the same CEL and codes within 12 hours and 10 miles after TSB completed for cold start rattle. Problem traced to bad gaskets in SAI system. But sounds like these codes could be indicative of a number of other issues.

[JD S4]

I looked at your connections and from up top they all look normal. Have you had the chance to pull the bumper and see how everything is working coming off of the secondary air pump

Not yet. Avoiding it - but more and more likely looking necessary


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[JD S4]

Got the same CEL and codes within 12 hours and 10 miles after TSB completed for cold start rattle. Problem traced to bad gaskets in SAI system. But sounds like these codes could be indicative of a number of other issues.

Another thing to think of - thank you


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[bhvrdr]

Not yet. Avoiding it - but more and more likely looking necessary


Sent from my

Yeah I understand. While pulling the bumper off only takes 20 minutes it does put you in a different frame of mind when you see the car that way.

It turns into a "we are not leaving here until I figure out what's wrong with you" frame of mind .

Start early in the morning because we all know how those frames of mind end. Usually with a greasy tablet screen from googling, 3 parts that are broken on the car that weren't before, two bloody hands, and four trips to Pep Boys and then come four o'clock in the morning she's good to go. But of course as far as Audizine will know it was a 30 minute job wink wink

[theweebabyseamus]

Yeah I understand. While pulling the bumper off only takes 20 minutes it does put you in a different frame of mind when you see the car that way.

It turns into a "we are not leaving here until I figure out what's wrong with you" frame of mind .

Start early in the morning because we all know how those frames of mind end. Usually with a greasy tablet screen from googling, 3 parts that are broken on the car that weren't before, two bloody hands, and four trips to Pep Boys and then come four o'clock in the morning she's good to go. But of course as far as Audizine will know it was a 30 minute job wink wink

He knows all too well, he's counseled (consoled? Lol) me on more than one of these occurrences.

[JD S4]

Lmfao. Exactly. ^^^^
I’d rather teach than learn. Worst part of this car shit is all the extra work that comes woth it.

Fuck it. In Vegas with wife and kids for cinco de mayo and have a cabana at red rocks today and tomorrow. Zero fucks on car.

Deal with it when I get back


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[Polo77]

I have the same code on my car been going on for a couple months. I just keep deleting the code. But it’s time I take my car into the dealer to get it fixed. I’m CPO. Should be covered? I’m assuming CW and Roc Euro intake should be removed


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[engineerjet]

I've brought my car in 3 times for those codes. This week will be the fourth. They have done the cleaning, replaced the kombi valves. They went back and forward with a tech from Audi and they thought it was fixed but this is the 4th time the code has come back and I just want it fixed. I'll keep you updated.

[jeremy@matrix]

JD, did the dealership smoke test the system for vacuum leaks?

[Bifffairburn12]

I have the same issue. After getting my intake valves carbon cleaning done I’ve been getting CEL codes for insufficient air flow bank 1. I clear them with my OBDELEVEN but they keep coming back. Worried that I won’t be able to pass inspection with the CEL on. Yeah I can clear the code before getting inspection but just putting a bandaid on a headache IMG_4170.JPG


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[Claudi-o]

I have this same issue and I live in Maryland which the state does the inspection meed to know how to fix this and my emmisions are due.

It actually happened after a
I pulled the SC to change thermostat, water pump and clean the carbon buildup... now I have the check engine and not sure how to tackle this

[Slenderjim]

Old but any updates? I have had this bank 1 code forever and I've had the carbon cleaning done, the pump works, air comes out of the hoses from the combi valves when it's on, solenoids work, relay is replaced......now what

[Manystylze]

For anyone coming here, hope this tidbit helps

I have been experiencing these codes for a few months now, and like most before, I just kept deleting them; however they were getting relatively more commonplace. Finally looked back in to it and found this videoo pointing out a 40amp fuse located near the ECU that is responsible for setting off these codes:

https://youtu.be/3S1c0vmoSJw

[shreddykrueger]

For anyone coming here, hope this tidbit helps

I have been experiencing these codes for a few months now, and like most before, I just kept deleting them; however they were getting relatively more commonplace. Finally looked back in to it and found this videoo pointing out a 40amp fuse located near the ECU that is responsible for setting off these codes:

https://youtu.be/3S1c0vmoSJw

any idea where exactly this fuse is? I was digging around the fuses near the ecu on the drivers side but couldn't find a 40amp anywhere. Ive been chasing these codes for months, recently changed the SAI pump and hear it kick on as well as change the combo valves but still having these CELs pop up

[SwankPeRFection]

any idea where exactly this fuse is? I was digging around the fuses near the ecu on the drivers side but couldn't find a 40amp anywhere. Ive been chasing these codes for months, recently changed the SAI pump and hear it kick on as well as change the combo valves but still having these CELs pop up

Did you actually clean the channel that runs from the front of the engine behind the freeze plug all the way back to the combi valves and has passages into each of the exhaust ports on each bank? Carbon will build up in it and causes restricted flow and when it gets below a certain expected level, these codes get set off.

[shreddykrueger]

Did you actually clean the channel that runs from the front of the engine behind the freeze plug all the way back to the combi valves and has passages into each of the exhaust ports on each bank? Carbon will build up in it and causes restricted flow and when it gets below a certain expected level, these codes get set off.

yes. looks like the T hose under the SC has a small tear that can only be faintly heard when the pump is running, everything else checks out. replacing that next week and should fix the issue

[shreddykrueger]

jk. even after replacing the sai pump, doing the SAI cleaning (again), pulling and cleaning the combi valves, and replacing the hose under the SC, the codes popped again this morning after cold start. no clue what the issue could be at this point, might just find a tuner to code it out I suppose

[JRYtheS4]

jk. even after replacing the sai pump, doing the SAI cleaning (again), pulling and cleaning the combi valves, and replacing the hose under the SC, the codes popped again this morning after cold start. no clue what the issue could be at this point, might just find a tuner to code it out I suppose

Damn. That's so frustrating. I have occasional codes for p0492 but it hasn't been consistent enough to stop me from passing inspection

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