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Discussion Starter · #1 · (Edited)
I don't have any engine lights but on scanning I have 2 codes about the secondary air pump:
P0411 16795-02
P1411 17819-02

There's a good summary of what to look for.

My Secondary Air Pump relay works correctly, I've tested it with voltmeter and 12V battery

But the installed relay part number is 7M0 951 253 A
but when I look up 7zap, it should be 1J0 906 381B (which is dearer)

Does the part number matter?

The air pump is brand new. The plastic hoses are not cracked.

But when I test the combi valve under vacuum, it doesn't open. So I guess this must be the culprit (021 131 101E).

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you've got the wrong relay imo all the right relays for the mk4 platform start with 1J0 ... 7M0 is for a Sharan.. now in most cases the parts can be swapped about but with electrical switches sometimes the internal resistance is different so best to get the right 1J0 counterpart (even though it is more expensive)
 

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Fault codes are for incorrect flow. Your combi valve is broken. Compare relay schematics (they are printed on the top of the relays usually). If they are the same, there is no difference. A relay is just a switch, it doesn't have internal resistors.
 

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A relay is just a switch, it doesn't have internal resistors.
most used on the mk4 platform are just switches... my daily though (GM build Vauxhall Vectra C)has resistors build-in some of the relays, mostly the ones for the exterior lights. think they are needed for the canbus setup as that car constantly checks the state of everything connected to it. It's also a nightmare to do oem upgrades as everything is coded to one another. So not al relays are just switches...
 
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