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P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow

P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

Possible cause of fault

- Electrical fault in power supply or line between relay and secondary air injection pump

- Secondary air injection pump relay mechanically faulty

- Mechanical fault in electrical secondary air valve

- Pneumatic secondary air valve faulty/sluggish

- Electrical fault in secondary air injection pump

- Mechanical fault in secondary air injection pump or secondary air injection pump blocked

- Vacuum system leaking

- Air hose to secondary air injection pump slipped off or constricted

post-1-1216429200_thumb.png

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  • 10 months later...

Hello:

I have the same codes with my 2002 996C2. Weird thing with my car is that the pump sometimes runs for a short period when I stop at stoplight, coming off freeway or after a steady 3 or 4 mile drive. I live in AZ, so don't think it's because engine is still cold. I've reset the CEL and observed that the CEL comes back on when I stop at stoplight. Usually not the 1st stop light, but a light 5 miles down the road. Since it's intemittent, and at wrong time, I suspect valves or vacuum leak.

Is there a diagram available for my car?

Thanks,

Dan

P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow

P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

Possible cause of fault

- Electrical fault in power supply or line between relay and secondary air injection pump

- Secondary air injection pump relay mechanically faulty

- Mechanical fault in electrical secondary air valve

- Pneumatic secondary air valve faulty/sluggish

- Electrical fault in secondary air injection pump

- Mechanical fault in secondary air injection pump or secondary air injection pump blocked

- Vacuum system leaking

- Air hose to secondary air injection pump slipped off or constricted

post-1-1216429200_thumb.png

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  • Admin
Hello:

I have the same codes with my 2002 996C2. Weird thing with my car is that the pump sometimes runs for a short period when I stop at stoplight, coming off freeway or after a steady 3 or 4 mile drive. I live in AZ, so don't think it's because engine is still cold. I've reset the CEL and observed that the CEL comes back on when I stop at stoplight. Usually not the 1st stop light, but a light 5 miles down the road. Since it's intemittent, and at wrong time, I suspect valves or vacuum leak.

Is there a diagram available for my car?

Thanks,

Dan

P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow

P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

Possible cause of fault

- Electrical fault in power supply or line between relay and secondary air injection pump

- Secondary air injection pump relay mechanically faulty

- Mechanical fault in electrical secondary air valve

- Pneumatic secondary air valve faulty/sluggish

- Electrical fault in secondary air injection pump

- Mechanical fault in secondary air injection pump or secondary air injection pump blocked

- Vacuum system leaking

- Air hose to secondary air injection pump slipped off or constricted

post-1-1216429200_thumb.png

Pretty much the same for your car - MY02 and newer 996 Carrera's use the same DME and most emissions components as 996TT.

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  • 6 months later...
Hello:

I have the same codes with my 2002 996C2. Weird thing with my car is that the pump sometimes runs for a short period when I stop at stoplight, coming off freeway or after a steady 3 or 4 mile drive. I live in AZ, so don't think it's because engine is still cold. I've reset the CEL and observed that the CEL comes back on when I stop at stoplight. Usually not the 1st stop light, but a light 5 miles down the road. Since it's intemittent, and at wrong time, I suspect valves or vacuum leak.

Is there a diagram available for my car?

Thanks,

Dan

P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow

P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

Possible cause of fault

- Electrical fault in power supply or line between relay and secondary air injection pump

- Secondary air injection pump relay mechanically faulty

- Mechanical fault in electrical secondary air valve

- Pneumatic secondary air valve faulty/sluggish

- Electrical fault in secondary air injection pump

- Mechanical fault in secondary air injection pump or secondary air injection pump blocked

- Vacuum system leaking

- Air hose to secondary air injection pump slipped off or constricted

post-1-1216429200_thumb.png

Pretty much the same for your car - MY02 and newer 996 Carrera's use the same DME and most emissions components as 996TT.

Hi Loren:

The information is really great. Thank you.

I've replaced the 3 valves, fixed a broken vacuum line (broken when replaced alternator) and replaced the "check valve" since it wasn't holding vacuum very well. I oriented the check valve so that there is nothing from the vacuum line entering the intake manifold. However, it gets me a periodic P0491 code. When I change the orientation, so that it's pulling air from the vacuum line, I haven't gotten a CEL, but throttle jumps up and down a little.

Can you advise the correct orientation for the check valve? Should it prevent air from entering the intake manifold or should it allow air to be pulled from the vacuum line? Is that where the secondary air system gets it's vacuum?

Final bit of information: when I take the vacuum line off the check valve, there doesn't appear to be any vacuum or pressure. Regardless of whether secondary air pump is blowing or not. Also, I tend to get just P0491, not both P0491 and P0492.

Thanks for your advice,

Dan

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I found the reservoir tank failed one time. It didn't leak using a smoke machine and I didn't find the leak until I submerged it under water and applied 1 PSI of air to it. Drove me around the bend trying to cure the secondary air codes.

  • Upvote 1
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  • 8 months later...

Hello:

I have the same codes with my 2002 996C2. Weird thing with my car is that the pump sometimes runs for a short period when I stop at stoplight, coming off freeway or after a steady 3 or 4 mile drive. I live in AZ, so don't think it's because engine is still cold. I've reset the CEL and observed that the CEL comes back on when I stop at stoplight. Usually not the 1st stop light, but a light 5 miles down the road. Since it's intemittent, and at wrong time, I suspect valves or vacuum leak.

Is there a diagram available for my car?

Thanks,

Dan

Hello all, I hve exactly the same problem. What did you find out was the problem?

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I have done searches all over and found very little. The car is a 02 996 Turbo and I have found no vaccum leaks, and the pump is running fine. Anybody else had any luck with these codes?

Check and see if the over run air valves ( #2 in the picture) are holding vacuum. I know it sounds funny but if one of those valves is leaking it will throw those exact faults.

Edited by PTEC
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Hello:

I have the same codes with my 2002 996C2. Weird thing with my car is that the pump sometimes runs for a short period when I stop at stoplight, coming off freeway or after a steady 3 or 4 mile drive. I live in AZ, so don't think it's because engine is still cold. I've reset the CEL and observed that the CEL comes back on when I stop at stoplight. Usually not the 1st stop light, but a light 5 miles down the road. Since it's intemittent, and at wrong time, I suspect valves or vacuum leak.

Is there a diagram available for my car?

Thanks,

Dan

Hello all, I hve exactly the same problem. What did you find out was the problem?

In my case, it was the vacuum canister. Had a crack. Drove me nuts but no CEL's since it was replaced a month or so ago. Something that helped me eliminate the valves was to cycle them off and on with my durametric. You can hear them click, can hear the pump come on. After that, knew it had to be a vacuum leak somewhere. Of course, the vacuum canister was the last place I checked...

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  • 1 year later...
  • 1 year later...

I had the same codes on my 02-996-C2-Cabbie. The line to the vacuum check valve at the resonance intake had dislodged as shown in picture and was a quick fix. But, the same thing happened again the very next day at 20 minutes into my drive. If it is holding vacuum, why would it pull apart? Should I suspect a bad check valve?, worn vacuum lines?, or check elsewhere? Or, should I just attach some hose clamps and see if that does it? Thanks for suggestions.

FYI-update. I have had no further incidents with this "dislodged" vacuum line. It was probably self-inflicted, accidentally loosened, and not securely enough replaced, after cleaning dried oil from the resonance intake. No clamps added or other action taken except to inspect rubber, "blow-through", and more firmly re-insert lines.

post-85898-0-76286000-1367755879_thumb.j

Edited by abcounts
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  • 1 year later...

Have a friend with the same fault codes on a 05 997s. 

 

What happened:

My friend did a run in his car, the car was warming up, might not have had full operating temperature. Upon accelerating he hit the rev limiter and the motor started running rough. 

 

When we used the Durametric on it the first time it had misfires in every cylinder except number 6 and running rough. After deleting and trying again, it now only misfires on cylinder 1 and still running rough.

 

What we have tried

  • detached the MAF
  • switched with my MAF
  • Deleting the fault codes with Durametric
  • Checked some of the hoses in the schematics mentioned above

Error codes:

  • PO492 - secondry-air system bank 2
  • PO491 - secondry-air system bank 1
  • PO3001 - misfiring cylinder 1
  • PO3005 - misfiring cylinder 5
  • PO3004 - misfiring cylinder 4
  • PO3004 - misfiring cylinder 4 (two of these acctually, but not a PO3006)
  • PO3002 - misfiring cylinder 2
  • PO3003 - misfiring cylinder 3

Any suggestions? Did your cars run rough when having the PO491 and PO492 error codes?

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Just having the p0491 and p0492 codes does not make it run rough.  It's only noticeable when at a stop light immediately after getting off the highway.  The vacuum lines are connected to the manifold, which I think cause the slightly off idle after running at ~ 3000 rpm on the highway for a time period.   

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I am in a Cayenne, but had that P0492 and it turned out pump had failed.  Impellar blades were all broken up.  Found another unit online.  Also had trusted Indy tell me that the air filter in front of pump gets brittle/dry rots after 10 years or so, will break apart, pump will suck bits through and snap blades...then blades get lodged and disrupt airflow.  so pump can be running because you hear the motor, but impellar blades are shot and its not really doing anything.

 

may not be your issue, but happened to me and Indy told me he has seen it a few times.  I was getting P0492 about once every couple weeks before I fixed it.

 

 

edit:  could not tell a difference in running rough/idle/etc and don't see how that would be related.

Edited by jpru2001
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The error codes PO492 and PO491 was the ignition system, we replaced all spark plugs and coils. Deleted the error codes and started, all fixed.

How many miles you've put on the car since then? It may take some time for the P0491/P0492 codes to come back after a DME reset.

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The error codes PO492 and PO491 was the ignition system, we replaced all spark plugs and coils. Deleted the error codes and started, all fixed.

How many miles you've put on the car since then? It may take some time for the P0491/P0492 codes to come back after a DME reset.

 

 

Hi Ahsai

 

We have tried various things prior to this, MAF replacement, just clearing the error codes. The error codes always reappeared after 30 seconds on idle. The engine was running rough with misfire on cylinder 1, it does not do that anymore. After one days use the car has no error codes, we must call it a successful DIY, my friend was very happy with the result.

Edited by Odd Arne Klinge
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  • 4 months later...

Hi All,

  I received the same code (0492). Recalling what happened before this code came up was that my battery depleted, just as I tried to start it, this code came up. I reset and drove around for 30 min, no more code.

Just my observation, this code was triggered when there was not enough power to the sensor/s thus producing the resulting code. After resetting it, my battery got depleted again, and again the code came back. Again I reset it, all is normal.

I will be replacing my Old Battery.

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  • 1 year later...
10 hours ago, Gavin Autowerks said:

Thanks for your help  with code P0491. After some diagnostic time I think it is the vacuum tank. Does anybody know where it's located

If it's a 996, the vacuum tank is behind the alternator. You need to remove the alternator to get to it. You may also need to remove the left intake manifold.

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