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Old 03-19-2019, 07:26 PM
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How to test secondary air injection valve?

Hi guys, I've been sporadically getting P0491 on cold starts so I removed the air pump, valve and all the hoses to see if I could find the problem. The hoses all looked good and I was able to supply current to the air pump which seemed to be working well. The only part I wasn't sure how to test was the egr valve. It didn't really seem to react to vacuum on the small line. I sprayed a bunch of brake cleaner in it and it seemed pretty dirty. I'm thinking I may need to replace it. Any tips? Thx
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Old 03-19-2019, 07:38 PM
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Which car is this on? At least on the 3.0, pre lci and lci sap systems are different. Early has a vacuum controlled valve while the later ones eliminate this and just use the air pumps pressure to work against the spring and force the valve open. If you can blow through it, it's fine. There's also a mini maf that goes bad and can throw the generic obd code. Inpa or equivalent will tell you.
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Old 03-19-2019, 07:48 PM
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Quote:
Originally Posted by e39_touring View Post
Which car is this on? At least on the 3.0, pre lci and lci sap systems are different. Early has a vacuum controlled valve while the later ones eliminate this and just use the air pumps pressure to work against the spring and force the valve open. If you can blow through it, it's fine. There's also a mini maf that goes bad and can throw the generic obd code. Inpa or equivalent will tell you.
This was on the 2002 4.6is. The valve has a large inlet and outlet hole and a small vacuum line which attaches to a black tube with a blue stripe that goes under the engine cover.
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Last edited by rwm514; 03-19-2019 at 08:01 PM.
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Old 03-19-2019, 08:12 PM
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Ok, no mini maf on that system. Basically, the air pump operates at startup, and the ecm looks for the added air to affect o2 values. If it doesn't see the change, it throws the code.

The air pump comes on at cold start and should produce a brisk breeze out of the hose if you disconnect it. To test the valve, apply vacuum to the vacuum line and blow through the big hose to the valve. If you can't, the diaphragm is probably holed.
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Old 03-19-2019, 08:16 PM
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Quote:
Originally Posted by e39_touring View Post
Ok, no mini maf on that system. Basically, the air pump operates at startup, and the ecm looks for the added air to affect o2 values. If it doesn't see the change, it throws the code.

The air pump comes on at cold start and should produce a brisk breeze out of the hose if you disconnect it. To test the valve, apply vacuum to the vacuum line and blow through the big hose to the valve. If you can't, the diaphragm is probably holed.
Ok Thanks,
I wasn't able to get air to flow through it, with or without vacuum to the small line. I guess its frozen up inside.
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