Secondary Air and MASS_SA_REL values

[slykens]

Hello all -

Like many with early B8 S4s, I've got the SAI codes for both banks. My car was cleaned just before 50k miles and now appears to be asking for it again at 134k - so driving it harder has extended the time between issues.

I pulled the TSB with the procedure and figured I'd go through the diagnostic portion to be sure before planning a DIY project like this since the local dealer ballparks $2500, the local indy shop won't do it, and the tool is going to cost a grand by itself.

Using vagcom I performed the "Checking Secondary Air System" procedure and then checked the values stored in the MASS_SA_REL[0] and MASS_SA_REL[1] blocks as per the TSB. The diagnostic procedure states that if the values are between 0.1 and 0.7 that the system needs to be cleaned. In my case the values were both 0.047.

Anyone with an idea of what that value actually means? The after values are supposed to be 0.9 to 1.0 so I can only assume mine is "terrible" and might be so low as to be a pump or a hose problem instead?

Thanks for any insights.

[djn876]

Should be pretty obvious if the pump runs, or if the hose has popped off or something.

You should be able to test with VCDS as well. That number is likely just a mass flow rate value in g/a or kg/hr or something like that.

I would agree it seems like you are below the normal detectable range, so could be another issue other than blockage and worth checking out.

What were the specific codes? Did the value fluctuate at all or was just hard downscale the whole time?

Sent from my SM-G988U using Audizine Forum mobile app

[slykens]

Well, I need to get some help testing this weekend where one person can trigger the test in the cabin and depress the pedals and I can get my head around the SAI pump.

The test is done with vagcom/vcds in Basic Settings in the Engine module. When I look at just the values out of the measuring blocks they are only 0 or 1 with the car warm so you have to conduct the test to get a real value populated as the TSB procedure says.

I will have to set up graphing on the codes to see if they fluctuate but the procedure is to run the test then immediately read the values from those blocks, which I did. The DTCs were P0491 and P0492 and appeared at the same time which led to this line of investigation.