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Discussion Starter #1
I have a 2004 vw Touareg and the secondary air pump relay switch is working but not being activated. The fuses are OK and I have 12v to the relay. I'm looking for the unit that activates it. Any help is appreciated.
 

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Discussion Starter #3
Hi TurboABA, Thank you for the great illustration but I'm looking for the location of the Cut-Off Valve 7L0906518 because I think it controls the ground side of the relay switch. I've checked the relay switch and it is working like it should. I have jumpered out the secondary pump at the relay switch location and the secondary pump works fine. I have 12v to the relay switch when the key is on to activate the relay switch. I'm looking for what tells the pump to turn on and off? Thanks again
 

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Discussion Starter #6
Hi TurboABC, Sorry for the long delay. Thank you for some more great illustrations. I have been able to find the first two but not the last one which points out where it is located. Thank you for locating it for me. I've been crawling all over that engine from the bottom and the top for many hours looking for that part. Thanks again. I hope this is the problem but I keep thinking that what ever turns the system on and off has something to do with a heat sensor or more complicated an oxygen sensor. If you or someone else knows, please let me know. Thanks
 

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Secondary air system

To heat the catalytic converters as quickly as possible, the mixture is enriched with fuel on cold-starting and during warming up. This results in a higher percentage of uncombusted hydrocarbons in the exhaust gas during this period.

Thanks to air injection downstream of the exhaust valves, the exhaust gases are enriched with oxygen, leading to oxidation (afterburning) of the hydrocarbons and the carbon monoxide. The heat released during this process also heats the catalytic converter, helping it to reach its operating temperature faster.

The secondary air system is comprised of:
  • the secondary air pump relay J299,
  • the secondary air pump motor V101 and
  • two self-opening combination valves
Input signals
  • Signal from the lambda probes (for system diagnosis)
  • Coolant temperature
  • Air mass meter engine load signals
Secondary air injection

The secondary air system is switched on during cold-starting, at the start of the warm-up phase and for test purposes as part of EOBD. In this case, the engine control unit actuates the secondary air pump via the secondary air pump relay. When the pressure which has been generated is present at the combination valves, they open and the air flows downstream of the exhaust valves. Afterburning takes place.

Function of the combination valves

The combination valves are self-opening valves. This means that they are opened via the pressure generated by the secondary air pump, and not via vacuum as in the previous secondary air systems.

Combination valve closed
The pressure in the combination valves corresponds to ambient pressure. The valves are closed.

Combination valve open
If the current for the secondary air pump is activated via the relay, it begins to deliver air. Pressure builds up due to the fact that the combination valve is closed. This is present at the valve disk and, via the hollowed-out valve stem, at the diaphragm. If a pressure of approx. 450 mbar above ambient pressure acts on the diaphragm and the valve disk, the valve opens.

The air delivered by the secondary air pump now flows downstream of the exhaust valves and afterburning takes place.
 

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Discussion Starter #8
Hi TurboABA, Thanks again for a great response. Now I need to check to see if the ECU is doing its job. I'll let you know if I can figure it out. Thanks again
 
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