2001 Audi A8 check engine light on

  • 2001 AUDI A8
  • 4.2L
  • V8
  • 119,000 MILES
Followed by fault codes 0491,0492 what's the solution to these codes?
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Tuesday, February 10th, 2015 AT 10:30 AM

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I had never heard of the air injection pump (The ABZ engine does not have the system, only the 00 and newer cars have it), but we found it in the airbox, on the suction side of the air filter. See photo number one

The Bently says to check the hoses and make sure the fuse is good and the motor works. Hook up the ross-tech software, do an output test and it starts testing all the components in the fuel injection system!

Get to the one for the air injection pump, it pulses 12 VDC to it and you can hear it spinning. But it doesn't seem to have any airflow, like whatever it is discharging into is closed. So we follow the hose and find that it goes here (hose is removed in picture, but the hose was just fine). See photo number two

The codes are P0491 & P0492. Secondary Air System Fault.

So we pulled the hose as shown in the picture above and did the output test again, and that air pump was blowin'!

So we looked at where it went and found that the diaphrams have to be activated to have the valve open and allow air flow. There is one at the aft end of each cylinder bank. What controls the diaphram you ask?

A vacuum line. So we follow the vacuum line and see that it goes here, which is on the top side of the left cylinder bank, mounted on the aft side of the fuel rail. See photo number three

The vacuum hose was disconnected, for some reason it was too short to reach it, we did a little rerouting of the hose and got it connected again.
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Friday, February 13th, 2015 AT 7:54 PM

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