Code P0491 Secondary Air Injection System Insufficient Flow

SALVADOR T MARTINEZ

MEMBER
2010 VOLKSWAGEN CC
2.0L
5 CYL
2WD
AUTOMATIC
93,000 MILES

P0491 Secondary Air Injection System Insufficient Flow. Stumped.
My VW CC 2010 is having a check engine light with the code P0491 which means the pressure sensor is not detecting enough air being pumped from the intake into the exhaust.

I have already:

Replaced the Secondary Air Pump

Replaced the Combination Valve (did not replace the gasket)

Replaced the O rings

Replaced the pressure sensor

Replaced engine air filter

Checked for leaks

Checked to see if the exhaust hole in the manifold was clogged

Full car details are listed above.

Engine: 2.0L TSI CBFA

6 Replies

SALVADOR T MARTINEZ

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4 POSTS

Adding images.

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Sunday, October 11th, 2020 AT 6:28 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

With that code, it sounds like you have hit nearly everything. Are you certain there are no leaks?

Also, have you confirmed fuses are good and the secondary air injector pump relay is good? I attached a few pics below. Pic 1 shows the fuses I am referring to as well as indicate it is fuse panel B which should be under the hood. Now, pics 2 and 3 are the same fuse box, but have a different layout based on early or late production.

Check the fuses as well as the relay. Also, make sure there is power to in and out of the fuses being checked. Here are a couple links you may find helpful:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know what you find.

Joe

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Tuesday, October 13th, 2020 AT 5:27 PM

SALVADOR T MARTINEZ

MEMBER
4 POSTS

I have the fuse box with the two relays. I checked all the fuses and # 28 was missing but I purchased one from AutoZone and put it in. I cleared the CEL and the code came back after two cold starts. Ill check the power when I get a chance and get back.

Where can I find diagrams like the one you provided? It's really useful to reference.

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Monday, October 19th, 2020 AT 7:32 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

We use two sources, Alldata and Prodemand. Both are excellent. They aren't free, but are reasonable. However, let me know if you need anything and I'll get them to you.

Let me know what you find.

Joe

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Monday, October 19th, 2020 AT 8:23 PM

SALVADOR T MARTINEZ

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4 POSTS

Thanks for the help.

You will not believe how I fixed this issue.

Yesterday, I checked the fuses which were for the secondary air system and they were all good.

As a last resort I thought about everything I had changed on the car that might be causing the issue.

A couple months back I was seeing some parasitic draw issues from the radio fuse. So I replaced the radio with one of the same part number off eBay.

I decided to put the factory radio back in and viola the CEL cleared right away. I ran the basic settings test that was failing before and now its passing.

Do they seriously store emissions related parameters in the radio of all things?

I'm 100% sure this was the fix as I have had this problem for months and as soon as I put the radio back in the problem goes away.

Now my question is, Why VW? What does the radio have to do with the secondary air injection system?

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Code P0491 Secondary Air Injection System Insufficient Flow

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