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Multiple Codes, Air Leak vs O2 Sensors


Go to solution Solved by rick3000,

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Hi Everyone,

I have been enjoying my Boxster with minimal issues since 2006. For the last year I have had reoccurring P01124 and P01126 codes, occasionally with P0455. These are normally associated with an air leak. I have replaced the gas cap, air/oil separator, and my mechanic did find a pin hole in a breather tube.

However, it did not complete stop these codes from popping up every now and then. I have taken the car two different Porsche mechanics and neither can find the leak causing this to reoccur. I have been experiencing rough idle at start and when warm, and at high altitude 4000'+ I have had some trouble getting the car to turn over.

Today I received P0455 fault and two new codes: P0134 pending and P0154 pending. These appear to be O2 sensor codes. I went through all of my records and cannot find any mention of the O2 sensors being replaced in the last 40k miles. Although they should have been a part of the 60k service, it is not listed on the invoice. I currently have 82k miles.

Could these O2 sensor codes/issues be causing the fuel mixture to be off, causing the previous P01124 and P01126 codes?

Should I DIY the O2 sensors, or should I take it in because it is likely more complex than just replacing the sensors?

Any other advice or experience would be greatly appreciated!

Thanks,

-Rick

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Hi Everyone,

I have been enjoying my Boxster with minimal issues since 2006. For the last year I have had reoccurring P01124 and P01126 codes, occasionally with P0455. These are normally associated with an air leak. I have replaced the gas cap, air/oil separator, and my mechanic did find a pin hole in a breather tube.

However, it did not complete stop these codes from popping up every now and then. I have taken the car two different Porsche mechanics and neither can find the leak causing this to reoccur. I have been experiencing rough idle at start and when warm, and at high altitude 4000'+ I have had some trouble getting the car to turn over.

Today I received P0455 fault and two new codes: P0134 pending and P0154 pending. These appear to be O2 sensor codes. I went through all of my records and cannot find any mention of the O2 sensors being replaced in the last 40k miles. Although they should have been a part of the 60k service, it is not listed on the invoice. I currently have 82k miles.

Could these O2 sensor codes/issues be causing the fuel mixture to be off, causing the previous P01124 and P01126 codes?

Should I DIY the O2 sensors, or should I take it in because it is likely more complex than just replacing the sensors?

Any other advice or experience would be greatly appreciated!

Thanks,

-Rick

P0455 is the code for a large vacuum leak in the EVAP system, often a loose, missing or defective gas cap. P0134 and 0154 are for a poor electronic connection (read loose plug) on both upstream O2 sensors. Find and fix the vacuum leak, clear the codes and see if the O2 sensor codes return; if they do, check all the harness connections before even thinking about replacement.

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Thanks, I'll try to resolve the P01124, P01126, and P0455 and check the harness before considering replacing the O2 sensors then.

I have recently replaced the gas cap and no one is able to find the air leak. Any tips on how I can troubleshoot this?

Even the mechanics are getting fed up with charging me to say we can't find it, I have taken it in at least 4-5 times with no luck finding this supposed leak.

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With rough idle, hard start, and no external leak located, is it possible the purge valve (beside the throttle body) is leaking?

The Purge valve should not trigger the EVAP related code he is seeing, but is worth a look in any case..

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Thanks, I'll try to resolve the P01124, P01126, and P0455 and check the harness before considering replacing the O2 sensors then.

I have recently replaced the gas cap and no one is able to find the air leak. Any tips on how I can troubleshoot this?

Even the mechanics are getting fed up with charging me to say we can't find it, I have taken it in at least 4-5 times with no luck finding this supposed leak.

Along with the gas cap, you could have a bad EVAP canister (cracked), a disconnected hose (there are several), a bad valve at the EVAP canister, etc. You could also have a fuel filler neck related issue, or simply an air leak into the fuel tank where the fuel pump enters. This is the kind of problem that the smoke machine to find vacuum leaks was developed for; quite often, visual inspection in not sufficient to find these leaks.

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Thank you for all of the replies!

The mechanics has previously used smoke machines to no avail. However, when I first got the car I had an issue with it rejecting gasoline at the pump and the dealer under warranty said a tube had slipped and they had to tie it back up into place. I would imagine that could be one of the things JFP in PA has suggested above.

Perhaps that could be causing the P0455 HVAC code, which appears in turn to be a possible cause of all these other codes, is that a fair assessment?

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When I had the 1124/1126 codes, I replaced the upstream O2 sensors, the valve by the throttle body, the valve on the EVAP canister, the two valves on the SAI system, the AOS tubes (even the AOS), all the 4mm vacuum lines, the vacuum canister (I broke it), IACV (and associated gasket), the oil filler tubes, gas cap w/ o-ring, oil cap w/ o-ring, dipstick o-ring, and tightened/retightened all the connections on the intake system. Might have been more, but can't remember right now. I didn't mind throwing parts at the problem because it was a 13 year old car and probably needed those new parts anyways. But none of it fixed my codes from reappearing. I eventually sold my car due to leaving the country for a while (don't worry, I'm not on the run...). I definitely disclosed the problem to the new owner, who was happy with my honesty, and bought my car and associated problem. I threw in an Actron code reader so he could verify those were the only two codes in the system and could reset the CEL whenever they reappeared. I still don't know what caused those codes. But it didn't affect power and it didn't affect mileage. And the codes would only appear after idling for five minutes (one of the emissions checks, but can't remember which one). Seriously, I did a 700 mile drive one day and the codes never reappeared. But as soon as I got off the interstate and had gone through a couple traffic lights, the codes came back.

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When I had the 1124/1126 codes, I replaced the upstream O2 sensors, the valve by the throttle body, the valve on the EVAP canister, the two valves on the SAI system, the AOS tubes (even the AOS), all the 4mm vacuum lines, the vacuum canister (I broke it), IACV (and associated gasket), the oil filler tubes, gas cap w/ o-ring, oil cap w/ o-ring, dipstick o-ring, and tightened/retightened all the connections on the intake system. Might have been more, but can't remember right now. I didn't mind throwing parts at the problem because it was a 13 year old car and probably needed those new parts anyways. But none of it fixed my codes from reappearing. I eventually sold my car due to leaving the country for a while (don't worry, I'm not on the run...). I definitely disclosed the problem to the new owner, who was happy with my honesty, and bought my car and associated problem. I threw in an Actron code reader so he could verify those were the only two codes in the system and could reset the CEL whenever they reappeared. I still don't know what caused those codes. But it didn't affect power and it didn't affect mileage. And the codes would only appear after idling for five minutes (one of the emissions checks, but can't remember which one). Seriously, I did a 700 mile drive one day and the codes never reappeared. But as soon as I got off the interstate and had gone through a couple traffic lights, the codes came back.

How well I remember.................

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Thank you for all of the replies!

The mechanics has previously used smoke machines to no avail. However, when I first got the car I had an issue with it rejecting gasoline at the pump and the dealer under warranty said a tube had slipped and they had to tie it back up into place. I would imagine that could be one of the things JFP in PA has suggested above.

Perhaps that could be causing the P0455 HVAC code, which appears in turn to be a possible cause of all these other codes, is that a fair assessment?

I always go back to the last thing touched when codes sudden show up. As mentioned, P0455 is the "large leak" EVAP system code, which obviously includes the gas tank; one neat trick in this department: Jury rig a rubber stopper or something similar to replace the gas cap (we actually took a new cap, drilled and tapped a hole in it that we then screwed in a threaded fitting to connect to a vacuum gauge) and check for a steady low vacuum on the tank with the car idling. If it is intermittent, or non existent, or worse yet there is pressure, there is a leak somewhere that has to be tracked down.

You can still have a loose connection on the O2 sensors as a vacuum leak is more prone to cause the car to throw overly lean O2 codes rather than a poor electrical connection code.

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Thank you everyone, I think this will be a job for the mechanic. Although, considering this previous mechanics track record, I am going to find a new one, and see if they have any better luck. I will recommend they try everything suggested here. I'll keep you updated, thanks!

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How well I remember.................

Haha! Yep. Thanks for all the help you've given me through the past couple years. I've definitely appreciated your experience and willingness to give advice.
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How well I remember.................

Haha! Yep. Thanks for all the help you've given me through the past couple years. I've definitely appreciated your experience and willingness to give advice.

You still in witness protection?

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  • 2 weeks later...

Yep, my car does the exact same thing as Bar10dah. And I've also replaced all those same parts to no avail. Definetly needed some of them like the oil filler tube and carbon canister. But yeah I can drive hundreds of miles on the interstate no code. Idle at 2 long lights and codes.

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Thank you for all of the replies!

The mechanics has previously used smoke machines to no avail. However, when I first got the car I had an issue with it rejecting gasoline at the pump and the dealer under warranty said a tube had slipped and they had to tie it back up into place. I would imagine that could be one of the things JFP in PA has suggested above.

Perhaps that could be causing the P0455 HVAC code, which appears in turn to be a possible cause of all these other codes, is that a fair assessment?

I always go back to the last thing touched when codes sudden show up. As mentioned, P0455 is the "large leak" EVAP system code, which obviously includes the gas tank; one neat trick in this department: Jury rig a rubber stopper or something similar to replace the gas cap (we actually took a new cap, drilled and tapped a hole in it that we then screwed in a threaded fitting to connect to a vacuum gauge) and check for a steady low vacuum on the tank with the car idling. If it is intermittent, or non existent, or worse yet there is pressure, there is a leak somewhere that has to be tracked down. (Emphasis added)

You can still have a loose connection on the O2 sensors as a vacuum leak is more prone to cause the car to throw overly lean O2 codes rather than a poor electrical connection code.

Simply ingenious! Thanks for the tip. I'm going to add it to my limited diagnostic bag of tricks! :thankyou:

Regards, Maurice.

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Thank you for all of the replies!

The mechanics has previously used smoke machines to no avail. However, when I first got the car I had an issue with it rejecting gasoline at the pump and the dealer under warranty said a tube had slipped and they had to tie it back up into place. I would imagine that could be one of the things JFP in PA has suggested above.

Perhaps that could be causing the P0455 HVAC code, which appears in turn to be a possible cause of all these other codes, is that a fair assessment?

I always go back to the last thing touched when codes sudden show up. As mentioned, P0455 is the "large leak" EVAP system code, which obviously includes the gas tank; one neat trick in this department: Jury rig a rubber stopper or something similar to replace the gas cap (we actually took a new cap, drilled and tapped a hole in it that we then screwed in a threaded fitting to connect to a vacuum gauge) and check for a steady low vacuum on the tank with the car idling. If it is intermittent, or non existent, or worse yet there is pressure, there is a leak somewhere that has to be tracked down. (Emphasis added)

You can still have a loose connection on the O2 sensors as a vacuum leak is more prone to cause the car to throw overly lean O2 codes rather than a poor electrical connection code.

Simply ingenious! Thanks for the tip. I'm going to add it to my limited diagnostic bag of tricks! :thankyou:

Regards, Maurice.

I have my moments; also did something similar for the oil fill to check the AOS.

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  • 3 weeks later...

I took my car into the dealer last week, they replaced a valve (996.605.201.01) and said they think they fixed it, they where unable to replicate the fluctuating/rough idle issue. I drove about 150 miles and they fluctuating idle has come back, and I had another instance where it fluctuated so far the car stalled when it dropped to about 200-300RPM and then did not want to turn back over, but eventually did. I parked, tried to turn it over again, no issue starting. Five hours later, I go to start it and it did not want to turn over, again.

There does not appear to be any catalyst or pattern to these issues, and this time I am not getting any codes. Any suggestions or thoughts before I take it back to the dealer? I really appreciate everyones help! Thanks!

EDIT: This could be a long shot, but I saw a mention of poor electrical possibly causing this type of issue. The dealer checked my battery because it is old (5-6 years). Would replacing it and seeing if that changes anything be worth trying?

Edited by rick3000
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I took my car into the dealer last week, they replaced a valve (996.605.201.01) and said they think they fixed it, they where unable to replicate the fluctuating/rough idle issue. I drove about 150 miles and they fluctuating idle has come back, and I had another instance where it fluctuated so far the car stalled when it dropped to about 200-300RPM and then did not want to turn back over, but eventually did. I parked, tried to turn it over again, no issue starting. Five hours later, I go to start it and it did not want to turn over, again.

There does not appear to be any catalyst or pattern to these issues, and this time I am not getting any codes. Any suggestions or thoughts before I take it back to the dealer? I really appreciate everyones help! Thanks!

EDIT: This could be a long shot, but I saw a mention of poor electrical possibly causing this type of issue. The dealer checked my battery because it is old (5-6 years). Would replacing it and seeing if that changes anything be worth trying?

The average life of a car battery is 4 years - after that they are always suspect. (IMHO)

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If your scanner can read real-time sensor values, it's worthwhile to check battery voltage, MAF, intake air temp, coolant temp, all O2 sensors, fuel trims, when you experience hard start, rough idle, etc.

Edited by Ahsai
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Thank you for all of the advice, I suggested a lot of these ideas when I dropped it at the dealer this morning. On the way there I recorded the tachometer with my phone at every red light. I was lucky enough to catch the exact moment it fluctuated, the CEL turned on, and the car made a high pitched gas escaping type sound.

I showed it to the mechanic, who said it is definitely not something common, like the MAF. He thinks it may be a failing purge valve, but they are going to do a pressurized smoke test. I will probably swap the battery out anyway before the temperature begins to drop.

I'll keep everyone updated on what they find, definitely an unusual issue, the mechanic said he had never heard anything like it.

UPDATE: They did a smoke/pressure test, and did not find any air leak, the car was operating within the normal/acceptable range. However, they said they found an old bulletin from Porsche concerning early 986's, that mentioned the two exact codes I have (P0446, and P1126) indicate replacing some kind of hose in the air system near the purge valve. I am hoping this will solve the issue.

Edited by rick3000
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The plot thickens, while waiting for the part referenced in the TSB, they attempted to do something to see if the purge valve was in fact bad. They then got a MAF code, and the car was turning over and dying. They replaced the MAF, but it still turns over and dies. No codes, so the mechanics are 'working on it.'

Edited by rick3000
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Thanks Loren, I will post when I hear what is happening, just in case it ever happens to anyone else. I seriously doubt it is any of the usual suspects, because most of them have been replaced at this point. I suspect some valve, or electronic problem but I have no idea. Last I heard the dealer mechanics where scratching their heads.

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