P0491 fault code

Hello everyone, I had a check engine light come up recently. Instead of spending $150 to have someone read it for me, only to have it come back on, I bought a Durametric code reader for $300. I was also curious to find out what sort of life my high mileage (160k) 996 C4S had lived. Turns out...it was charmed life with exactly 1 rev in range 2 and a few hundred in rev range 1. Best part is that the most recent rev range 1/2 events happened at 30k miles. Yeah! But I did find a few faults that led to the check engine light: P0300 misfire detection porsche fault code 507 P0302 misfire cylinder 2 porsche fault code 510 P0303 misfire cylinder 3 porsche fault code 512 P1325 inlet camshaft 2 porsche fault code 901 P0491 secondary air system bank 1 porsche fault code 80 Cleared all the code. Did a spirited drive (aren't they all with a 911?), everything ran and sounded great, then saw the lovely check engine light again. Checked at home, found these codes: P0491 secondary air system bank 1 porsche fault code 80 P1325 inlet camshaft 2 porsche fault code 901 Any suggestions? Assuming the secondary air pump needs replacing, how difficult is that job?

bump?!?

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I just got done replacing all the parts for that system all the vacuum hoses and valves are tough. I recommend when the car is dead cold open the engine bonnet and listen or pull off the hose on the secondary air pump. It should run for about 90 seconds. If it doesn�t run it�s a very simple swap out. Remove 1 nut and two bolts then remove hose and electric plug and it comes right out 5-10 minutes

I'll respond to my limited ability since I'd looked into buying a very cheap 996 that needed a secondary pump (with other things), that and it seems threads asking if you "talk to your car" rank higher these days. Good move on the durametric vs a $150 diagnostic fee. It's like getting it for half price. That is my thinking too, if I ever get a code but haven't yet, so I keep my fingers crossed. The secondary pump resides inside the engine compartment, driver side, just left of your knee cap when you open the hood, held by three bolts (IIRC) very easy to diy replace. It does cost almost $400 so you will want to check fuses and test it with 12v to be sure it has actually failed. You should be able to test in place too, applying 12v and disconnecting the air outlet checking for strong airflow. Since all these codes hit you at once I'd suspect your real troubles are elsewhere, plus they are all bank-1 related. I doubt you have coil problems (the missfires) as they don't likely fail more than one at a time. The camshaft code seems the most troubling. Since you have the durametric I'd check your camshaft deviations to see if you have a failure of the pads or actuator on bank-1. There are ways to check this too before digging in. You didn't say it started running rough when the codes hit so I'd still hope for the best. Even better advice would be to hit up Porschetech3 as he is most knowledgeable here, but post those deviation numbers too.

SAI pump is easy. Be careful with the plastic hoses. They're all really old and will break if you look at them wrong. Here's a link to a P1325 diagnosis that has links to other diagnosis. It looks like there are a number of causes from variocam solenoids to wiring to DME to camshaft. It seems the first step is to use your durametric and see if the cam angle is reacting to the solenoid activation. Good luck! https://www.renntech.org/topic/49783...comment-288701

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This does look quite easy. Just looked under the hood. I was expected my first engine repair to be a baptism by fire of reaching blindly into the nether region. I think the first thing to do is confirm the operation of the SAI pump in the car. Looks like a single 2 wire connector, so not much confusion about which contacts to use to run it manually with 12V. I think I'll disconnect and start the car cold to confirm that 12V is being sent to the pump for 90 seconds. Assuming yes at start, then no after ~90s, I'll pull off the single hose, which I assume is the output, apply 12V, and feel for airflow. Will report back after. Thanks for all the responses. BTW is bank 1 driver or passenger side?

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Bank#1 on LHD 911 cars is on the driver's side.

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I couldn't easy remove the connector to the SAI pump, but I was able to get the hose off easily. Looks like there was a hose clamp on at some point based on the marks, but no longer. I couldn't find a datecode, but the hose feels pretty soft and pliable. It has a 996 PN and is made in Spain - seems like a replacement hose? With the hose off, I started the car (cold) and the SAI ran strong for 90 seconds. So something else is triggering the SAI code. The hose feels pretty easy to turn, as if the other end is not well attached to the car. I reached around and couldn't reach to the end of the hose, so I can't confirm. That would be an easy fix...if I could get to the far end. Looks like removing the alternator (sorry Phase Generator) is the only way to get to it. Any suggestions? The Phase Generator was replaced by the PO about 15k miles ago.

U r on the right track. Pull the alt and u can inspect the hose, vac lines and the change over valve. With a bi-directional scanner ot duremetric u can activate the change over valve or pump at anytime to isolate the problem.

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OK, any tips to remove the alternator? Looks like there is an idler pulley in the serpentine belt, similar to my BMWs. Crank it clockwise and release serpentine belt. Then a couple of bolts for the alternator. How do I remove the positive and negative cables from the alternator? Any tricks or will it be obvious? Should I disconnect the battery first?

ABSOLUTELY YES! Disconnect the battery before removing the alternator. There are live wires back there.

Search google for the proceedure. Its been posted up 100 times. Biggest issue is when the upper bolt is tighted during install a floating sleeve wedges into the aluminum bracket. It can make the alt real tight. U need to be carful on prying it out and not break the bracket because its very expensive. Sime have been able to tap the sleeve over a hair to free it all up.

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Remove the alternator wasn't much fun, but at least I didn't break the bracket built into the alternator. (The alternator was recently replaced by the PO) I can confirm the far end of the secondary air pump hose is firmly connected at both ends. It looks like there is a valve at the far end. How can I test that? If the valve won't open, then I could see how that would throw the SAI code. I have a Durameteric scanner. How do I use it to "activate the change over valve"?

You�ll need to hook vacuum pump up to that little vacuum hose. Put a little seafoam in the big hose coming from the pump. It will make your cats smoke massively once it�s open, if the pump wants to blow off the hose at start up it�s not opening. the vacuum of the engine is around 20�hg with no leaks so it should open and close before that a new one will open close less then 10 in hg I believe. I would just remove it and buy a new one they get sticky it�s not that expensive of a part, I replaced that the vacuum bottle and the two changeover valves as well as the hoses for under 200$ I believe making the system like new, pelican has all the parts you may with the durametric be able to trigger the changeover valve that lets the vacuum go to that valve. One changeover valve allows vacuum to that valve to warm up cats. The other opens up to allow vacuum to trigger the flap in the rear crossover plenum between the intake manifolds. You�ll need to test it with the engine on. If your big pump is running you have 1 of 3 issues 1. changeover valve not activating or is leaking air. 2. Vacuum bottle or hoses are leaking air (test with a vacuum gun kit you can at auto parts for 30$ 3. Vacuum valve is sticking I think mine had all the issues so was worth just replacing it all. kinda a pain but if you remove the two crossover plenums and lower the engine on the two front bolts by unscrewing them till the max on the threads without removing you will have room to reach back and do it

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Doing some research in the repair manual and parts catalog: Change-over valve is the rectangular pneumatic-electric actuator in the picture. There's a second one that's easier to get to. Cheap and easy to replace, so why not? Vacuum tank looks like a serious job to replace. I will put that off unless nothing else works. Hoses I will order and replace anything that I remove What is the "vacuum valve?" The big silver thing in the middle of the picture? That looks (and feels) like a major job to swap out. I think I'll order the change-over valves and hose/pipe parts and replace what's easy to get to. Then I'll put everything back in and see what happens. Not sure if it's worth it to put the battery in and try to actuate valves with the Durametric. Might be a good next step after putting everything back in and doing a road test.

Two changeover valves one actuated the vacuum actuated flap in the rear plenum, I think at 5000 rpm that valve opens, the second one harder to get to actuated the valve your talking about that allows the pump push air through the block to headers and then the cats. they usually fail in that they leak air so lose vacuum. it�s a 4 hour job if you buy all the parts.

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So the idea with the Seafoam is to spray it into the hose between the secondary air pump and the valve at the block? Then start the car and if the exhaust blows a bunch of smoke, then air from the pump is getting into the engine and doing what it is supposed to? If I have that correct, then I'll swap the changeover valves, put everything back together, drive can and see if the CEL comes back on. If it does, then I'll let it cool down and try Seafoam. If not smoke, then there is something else preventing the SAI from doing its job. If yes there is smoke, then the SAI system is fine and something else (like camshaft sensor or actuator) is broken.

Yeah you got it. system is actually pretty simple. Computer on start up below a certain temp sends a signal to open changeover valve. That routes vacuum that was fed from the plenum over to the sai valve. The computer also sends a start signal to the pump and now that the valves open it can pump air through to the Sia valve. should be about 20psi of vacuum on that system at idle with no leaks it feeds 3 things Changeover valve for sia valve, changeover valve for plenum flap and if you have a tiptronic a vacuum hose is routed to the tranny.

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I swapped both changeover valves. Not a fun job, but not the worst ever. Getting the alternator out without breaking it was the hardest part. (Especially cause the alternator is new-ish, so having to replace it would have sucked.) I brought the car in for SMOG twice, but they said that the "SAI monitor" hadn't been run yet. Before I did the work, I tried clearing the code a couple of times, but the CEI light came on within minutes of starting the car. I didn't clear the code before doing the work. After everything was put back together, I started the car and no CEI light. Yea! I didn't clear the codes or doing anything, just shut it down, then started it a few days later to take it for SMOG. So I wasn't surprised to hear that maybe a "monitor" hadn't run yet. They said it might take 100 miles. So I drove the car about 6 times, including a 120 mile roundtrip. Brought car in again, same issue. I got home and checked the fault codes. Still showed the old P0491 SAI code. I cleared the codes. Did a couple of drives for about 30 miles. No CEI light. Checked codes when I got home, zero fault codes. Do I need to do anything else? Or can I take it to for SMOG now? The shop has been very polite, but I don't want to waste their time, or mine.

Don't take it back to smog until you know that the readiness monitors are set. No codes and no CEL does not mean monitors are set. I was under the impression that most scanner would tell you about the status. I have a cheapo OBD scanner for my non Porsche vehicles that shows the monitor status. Of course, Durametric shows it. I have a VAG-COM for my VW's that has a procedure to actually run the tests to set the monitors, it's really nice to have. I would expect there is a Porsche equivalent, PIWIS?

Google ,drive cycle for Porsche 996.

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I have a Durametric reader. How can I check monitor status with Durametric?

here's a picture from the online manual. Just click the left menu item 'ready status'. It will show the status of the monitors. Apologies that I don't have the next photo. I don't have my car right now. Good luck.

Thanks for the quick responses. 1. I cleared the faults last night 2. I did the drive cycle today 3. Got home, checked with Duramteric. Can see that all five monitors are READY. Looking good.... 4. I checked the entire fault codes: P0491 is back. Damn. No CEL. If I take the car to SMOG now, will it pass? The monitors are ready, no CEL, but do have the P0491 fault code. My guess is this will cause the car to fail SMOG. But maybe there's different thresholds and this will pass even though Porsche still sees some issue with the SAI system? Wishful thinking, I'm sure, but I want to check before I go and clear codes and see if there is anyway that I can get the monitors to clear before the P0491 code comes up. Doubtful but I've only got about two weeks to registration due date.

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Update: I took a chance and WAS able to pass SMOG with the P0491 code. Remember that I had a CEL that would come right back after clearing codes. After swapping the changeover valves, the CEL didn't come back after 200+ miles of driving, but the P0491 code is still there. So maybe the P0491 is a higher-level error that isn't enough to fail OBDII SAI check. (The SMOG report confirmed SAI passing) Also, I only bought the Durametric earlier in 2021. I've never checked codes after 5 years owning the car. It passed SMOG by the PO when I bought it, then twice again myself. (I've only put 6k miles on the car.) So it's possible this P0491 code was there all along, and the car passed SMOG many times by multiple SMOG shops.

Nice! Curious that it passed with a code. Mysteries of the smog check system. Maybe the more interesting thing is how it can pass readiness if something is just wrong enough to throw the code. Ah well... It's out of mind for the next years! Drive and smile!