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We just bought an 2004 Cayenne S and it's throwing a CEL for P0491-Secondary Air Injection Sytem. I cleared the code and it came back within the last 3 days. My questions is where is the Vacuum system located at on bank one and oriented on the car? I'm pretty positive it's probably a vacuum line came off or something minor to fix. Any help will be greatly appreciated.

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  • Admin

P0491 Secondary Air Injection System, Bank 1 - Below Limit

Possible cause of fault

- Fuse F3 faulty

- Open circuit to secondary air injection pump

- Short circuit to ground in the lead to secondary air injection pump

- Secondary air injection pump relay mechanically faulty

- Secondary air valve sluggish

- Secondary air injection pump (air cleaner) blocked

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

- Secondary air injection pump faulty/stuck

post-1-0-19838600-1296835394_thumb.jpg

1 - DME control module

2 - Secondary air injection pump, bank 1

3 - Secondary air valve - mechanical, bank 1

4 - Oxygen sensor in front of catalytic converter, bank 1

5 - Pre-catalytic converter, bank 1

6 - Oxygen sensor after catalytic converter, bank 1

7 - Main catalytic converter, bank 1

8 - Secondary air injection pump, bank 2

9 - Secondary air valve - mechanical, bank 2

10 - E-box in radiator tank with fuse and relay carrier

11 - Main catalytic converter, bank 2

12 - Oxygen sensor after catalytic converter, bank 2

13 - Pre-catalytic converter, bank 2

14 - Oxygen sensor ahead of catalytic converter, bank 2

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  • 5 years later...

I found a blown fuse for pump bank 1, replaced fuse and it immediately blew upon cold start up. What should I test to determine cause. Cayenne has 188,000 miles. no problem til this. Also at same time, maybe a coincidence, shifting noise coming from rear of car at 20 mph or less when in stop and go traffic, speed up and then let off throttle and something knocks from back of car. Does emissions pump failure affect this?

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30 minutes ago, jrgcom said:

I found a blown fuse for pump bank 1, replaced fuse and it immediately blew upon cold start up. What should I test to determine cause. Cayenne has 188,000 miles. no problem til this. Also at same time, maybe a coincidence, shifting noise coming from rear of car at 20 mph or less when in stop and go traffic, speed up and then let off throttle and something knocks from back of car. Does emissions pump failure affect this?

Only used for cold start 20 seconds to heat up cat and dilute emissions briefly apart from that totally useless. I deleted mine both don't work. Throws a code occasional but no dtc and no affect on running. Just ignore unless you want spend money or are in cold climate and extremely environmentally conscious. Driving a v8 ha ha Lol. 

I stripped both mine apart and found to be full of soot because the check valve (see pic 1) from the exhaust connection was stuck open. I used a 3/4" metal GI end plug to close the rubber pipe and problem solved from leak. The fins inside will be broken and that's the cause of the code also if the motor is jammed or toasted the fuse will pop also. Pic 2 foam filter is like a lump of charcoal inside is toast. 

IMG-20160410-WA011.jpg

IMG_20160425_150909.jpg

IMG_20160425_150926.jpg

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  • 9 months later...

Hi all.  I know this is an old thread but all the problems I have seem to be already discussed in pretty good detail.  This one I am mystified.  I have checked: Pumps & their filters, visibly physically OK; fuse F3, OK; hoses at valves, OK; connectors to pumps seem fully engaged... but with the covers off of the pumps, the blades visible I can see that NEITHER of them spins on cold start.  I say "cold" start, it was the first start of the day even thought it was midday 80 degrees.  I figured they should run.  It seems there are two relays for these pumps in the water box but it seems so unlikely that they both went out.  Does anyone know if there is an interaction between these two pumps in the system... like if one doesn't work, will the other one just not run?  Code just says bank 1.  Any insight would be a big help!

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4 hours ago, neoplanet said:

Hi all.  I know this is an old thread but all the problems I have seem to be already discussed in pretty good detail.  This one I am mystified.  I have checked: Pumps & their filters, visibly physically OK; fuse F3, OK; hoses at valves, OK; connectors to pumps seem fully engaged... but with the covers off of the pumps, the blades visible I can see that NEITHER of them spins on cold start.  I say "cold" start, it was the first start of the day even thought it was midday 80 degrees.  I figured they should run.  It seems there are two relays for these pumps in the water box but it seems so unlikely that they both went out.  Does anyone know if there is an interaction between these two pumps in the system... like if one doesn't work, will the other one just not run?  Code just says bank 1.  Any insight would be a big help!

Does the car run poorly on cold start? Like a bit lumpy or pulsing? 

Both of mine didn't work and it made absolutely no difference. To be honest if there is no effect and considering the purpose is for warming up the cats a bit quicker, then I wouldn't worry about it. Unless you want to spend some dollar that is and probably one or both pumps are knackered. Motors just burn out, or get seized or the impellor smashes apart and dumps into the pierberg check valve shown in my first picture. Also codes can mean the air flow from that pump is not sufficient, this could be blockage or simply doesn't run. 

 

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Thanks.  Yes, I wouldn't worry about it except that I live in California and have to get it to pass smog to get it registered.  They will require it be fixed.  I did test the impedance of the pump the code indicates is faulty and it shows continuity, so no blown out pump according to the troubleshooting steps in the factory service manual.  And the pump looks totally fine physically.  Nothing has fallen apart.  I'll try the relay and see what happens.  Just wondering if one being out could affect the other one by just shutting down the whole system in the computer.  I know this happens with the cornering head lamps.  One burns out, the other stops working.

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