P0491 - The Woes of the Secondary Air Pump

Hey guys,

Back at it again with some discussion. As some of you are aware of from my build thread, ever since I installed the K04 I've had a CEL pop up on random mornings. It seems to happen so random that I cant pinpoint an accurate trend. It seemed to happen every morning when it was REALLY cold, but then this morning it didnt do it. So I'm at a total loss and would like some other brains thinking on this. Here is the original Scan:

1 Fault Found:
001169 - Secondary Air Injection System: Bank 1
P0491 - 000 - Insufficient Flow
Freeze Frame:
Fault Status: 01100000
Fault Priority: 0
Fault Frequency: 1
Mileage: 65873 km
Time Indication: 0
Date: 2000.00.00
Time: 12:37:14

Freeze Frame:
RPM: 1758 /min
Load: 14.1 %
Speed: 0.0 km/h
Temperature: 18.0°C
Temperature: 17.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.970 V

Readiness: 0010 1001

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I contacted Arin yesterday and got a explanation back about what the code is and what its looking for. I'm a little foggy about how to interpret the secondary parameters and what engages the air flow testing from the secondary pump. Heres what I got:

DTC: P0491
Error Message: Seconday Air System - Insufficient Flow
Diagnostic Procedure: Check the Secondary Air Combination Valve
Malfunction Criteria and Threshold Value: SAI Pressure sensor vs. Modeled pressure < 0.62%
Secondary Parameters:

• MAF = 7-150 kg/h
• Delta Engine Load = -10% - 10%
• ECT = 5*C - 60*C
• IAT = 5*C - 40*C
• Altitude < 2700
• SAI Pressure Sensor, Ready = No Fault

Monitoring Time: 18.5 sec
Frequency of Checks, MIL Illum: 2 DYC


I obtained VAGCOM last Friday and have been playing with it since then. Upon some intense googling, I found I could ACTUALLY log the startup process of the SAI pump and if the test went well or not. (Reference: Group 77 - Air Mass from Sec. Air. Inj. bank 1 %)



I have no clue what is causing it to do a system check or why there is a delay from the start, but the fact that the SAI Pump is not pulling air during that entire system check looks to me like a shit valve. I'll double check the relay and make sure its not fried before I do a vacuum test of the system. But the valve seems to be moving. Seeing that the air mass is -100% before startup, 0 during testing, and -53.9% after it failed lets me know the combination valve is opening and closing, but why is it closed during the testing phase? Is there something in the software from preventing it? I dont want to swap out the valve and not have it work.

I want APR's POV on this as well, maybe Arin can talk to Chris about this, but aside from vacuum testing the system, I'm at a loss. Anyone have a part diagram of the SAI? I'll also check the breather filter attached for any clogs.

I have 3 other logs where the CEL did not come on...these will be posted shortly. EDIT: Seems there is a passive routine for allowing a certain number of checks before a CEL/MIL

I know this is the cheater's way, but you could always just remove it.

Bender said:

I know this is the cheater's way, but you could always just remove it.

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I could, but a Constant CEL isnt something I would want. I could see if APR could eliminate it but I wouldnt want it to negatively effect my 02 sensors, etc. etc.

No one care to comment?

Here ya go: http://www.golfmk6.com/forums/showthread.php?t=23225

http://forums.vwvortex.com/showthread.php?5406184-DIY-SAI-Delete-on-CBFA-Engine

Been watching this thread for a while.....its good but unfinished. There are some resistors that can be used to fool the cel and basically everything is there to cancel the sec air inj. I think maybe the cel has not been completely cancelled yet or not enough ppl have tried it. I would love to get rid of mine as it would be quite easy otherwise. Would be nice to make a sticky thread about it and add to it as other members work on it because it is eventually going to work one way or the other.

dsm1983 said:

Here ya go: http://www.golfmk6.com/forums/showthread.php?t=23225

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OMG Beaten to the punch by a min. by another Dave. Thats funny.

Edit: Well I didn't refresh my screen so that didn't help lol

I've been waiting for mk6 to tackle this one for a bit.

GunMetalGTI said:

OMG Beaten to the punch by a min. by another Dave. Thats funny.

Edit: Well I didn't refresh my screen so that didn't help lol

I've been waiting for mk6 to tackle this one for a bit.

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yeah, hopefully one of those vendors (IE or INA) will pull the trigger on a complete solution. I just don't want to sit there and buy 3 or 4 of their different resistors with the hope that they'll foul the CEL.
There are two sensors that plug into the Solenoid Secondary Air Valve, and one that plugs into the Secondary Air Pump. So three total -- let the trial & error begin. :thumbsup:

dsm1983 said:

yeah, hopefully one of those vendors (IE or INA) will pull the trigger on a complete solution. I just don't want to sit there and buy 3 or 4 of their different resistors with the hope that they'll foul the CEL.
There are two sensors that plug into the Solenoid Secondary Air Valve, and one that plugs into the Secondary Air Pump. So three total -- let the trial & error begin. :thumbsup:

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Ya for sure. I'm sure they will eventually. I would imagine something would work as long as they have the proper connection for them all. If its not a variable sensitive sensor maybe even jumping the connector with a fuse or something would work. I've done that before to say something like a windshield washer pump level sensor.

Again, I am not going to delete the SAI. Its more work than is needed to be done and until theres actual VAGCOM to eliminate it altogether, this simply isnt an option. It would be easier if it was a bad relay or a pinch in the system from the install.

It just seems to coincidental that it started happening after my install. That makes me believe I managed to loosen a hose or crack tubing somewhere when I had my hands up my GTI's skirt.

yea....I agree. I would try it but I have to pass emissions in the next six months. Don't feel like taking the risk of it still being an issue. I'm in MD and I'm catless but I should pass otherwise.

grambles423 said:

Again, I am not going to delete the SAI. Its more work than is needed to be done and until theres actual VAGCOM to eliminate it altogether, this simply isnt an option. It would be easier if it was a bad relay or a pinch in the system from the install.

It just seems to coincidental that it started happening after my install. That makes me believe I managed to loosen a hose or crack tubing somewhere when I had my hands up my GTI's skirt.

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I understand you're not trying to delete the SAI.
I posted because the thread has an exploded diagram of the system.

dsm1983 said:

I understand you're not trying to delete the SAI.
I posted because the thread has an exploded diagram of the system.

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I saw that and found it helpful, but where exactly did you get it? I'm thinking I can use part numbers to accurately detail whats going on and maybe search through vagcom for some sort of fix.

If I prowl the label file enough, there might be some sort of SAI bit I can modify to shut the damn thing off.

EDIT: NVM found it.

grambles423 said:

If I prowl the label file enough, there might be some sort of SAI bit I can modify to shut the damn thing off.

EDIT: NVM found it.

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PLEASE SHARE! :thumbup::thumbup::thumbup:

dsm1983 said:

PLEASE SHARE! :thumbup::thumbup::thumbup:

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I found the part numbers, not the extension in the label file lol Sorry to get your hopes up.

I see this being a multitude of things right now:

- Combi Valve shot to shit (Seems resonable)
- K04 not allowing breather air into block efficiently (I sure hope not...if so the SAI delete will be required for CBFA K04 users)
- Downpipe not allowing breather into block efficiently....???Doesnt make sense though
- Clogged SAI Filter (Not likely since I was able to breathe through it this morning)
- Loose combi valve vacuum line (Seems plausible)
- Faulty Coding within ECU from APR. (Doubtful)
- Bad Sensor in the tract

Could be a combination of these things as well. Objectively, the data shows there is no air mass moving across the sensor when system testing is activated. Whether that means the sensor is crap or the valve is stuck close, we wont know until we test.

Stay tuned, hopefully I can work on this this weekend.