[Tebessi]

Hello,
I have 2015 passat 1.8 tsi limited. I got the P0491 code and I am trying to do some diagnostics. I am trying to locate the secondary air pump relay but I don't know why I can't
find the fuse box diagram for this model. I looked everywhere but with no luck.

 

[Alpinerunner]

Bump. I have the EXACT same engine bay fuse box layout and I can't find a diagram that looks like this anywhere!! I've looked at youtube videos and the 49 page PDF of all possible fuse box locations and configs. Car is a 2014 Passat with 1.8L TSI motor. I'm also looking for the SAP relay location.

 

[Tebessi]

I found it. It is the big green 644 in the bottom.

 

[Alpinerunner]

Awesome! Thanks. Was yours blown? Is there also a fuse in the circuit? I’ve seen mention of a 40A fuse.

 

[John_E]

Make sure it is really bad before changing it. On a cold start, you should be able to hear the secondary air pump spooling up and then winding down when you turn off the ignition.
You can also remove the relay and insert a jumper wire to bypass its contents, and then listen for the air pump with the engine off. This will verify the 40A fuse, the pump motor, and the associated wiring.

If you have access to a VCDS, it will allow you to energize the air pump, as well.

When I ran the secondary air readiness prep. routine with my VCDS, I got -100% of expected air flow. The problem turned out to be one of the two small (and expensive) solenoid-controlled vacuum switches that sits on a plate tucked under the intake manifold.

 

[Tebessi]

The pump runs fine when I command it with obdeleven. But I am still having the P0491 code (insufficient flow)

 

[Alpinerunner]

Make sure it is really bad before changing it. On a cold start, you should be able to hear the secondary air pump spooling up and then winding down when you turn off the ignition.
You can also remove the relay and insert a jumper wire to bypass its contents, and then listen for the air pump with the engine off. This will verify the 40A fuse, the pump motor, and the associated wiring.

If you have access to a VCDS, it will allow you to energize the air pump, as well.

When I ran the secondary air readiness prep. routine with my VCDS, I got -100% of expected air flow. The problem turned out to be one of the two small (and expensive) solenoid-controlled vacuum switches that sits on a plate tucked under the intake manifold.

So far I’d determined that the pump does not run at all on cold start, it did not run when I jumped the relay mentioned above, and the car still ran when I swapped the 2 644 relays. I read somewhere that the other was fuel pump. So we can rule the relay out. All the 40A square fuses look good and I got power on one side of the relay so I think that rules fuses out.

Do you have any more info this vacuum switch? Is there a good thread that show access to it?

 

[Alpinerunner]

The next step will be to remove the pump and power it with 12V directly.