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MAF, multiple error codes, O2 sensor, toast?


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Hello everyone,

I'm in a world of hurt as my beloved '98 Boxster (81K miles) apparently has some serious issues and I'm looking for direction and/or assistance. First, the car seems to run fine after a brief warm-up. The issue is that the check engine light is on (I can't get it smogged or registered with the DMV) and when I took it to the Porsche repair place I use they came back with this:

CUSTOMER STATES: "CHECK ENGINE" LIGHT ON

SCAN SYSTEM FOR STORED CODES AND RECORD: P1121. P0160, O2 SENSOR

CIRCUIT NO ACTIVITY DETECTED (B2S2). P1117, P1128, P1130, P1123,

AND P1125. NO DRIVE CYCLES ARE COMPLETE.

EVALUATE LIVE DATA. FUEL TRIM BANK 1 IS 32% AND BANK 2 31%. O2

SENSOR, B2S2, IS FLAT. O2 SENSOR, B1S2, IS NON RESPONSIVE.

I talked with the mechanic and he said I could potentially pour thousands into the repair and it still not be addressed as it could also be an electrical issue. I'm tempted to try to replace the MAF and any other parts myself except that I've never done anything even remotely close to this and I'm concerned about turning the car into a large silver paperweight. Has anyone ever encountered these issues before? Any ideas on the cost of parts? Also, any mechanic mentors out there willing to work with me if I decide to move forward with working on it (I'll pay you of course for your tutelage)?

Honestly, I LOVE this car and am hopeful I can get this addressed. Thank you for your time.

All my best,

Gabriel

Roseville, CA

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  • Admin

The codes (all of them) point to a bad sensor (unless it is disconnected) on bank 2 (cylinders 4-6).

I would replace that one sensor (especially with 81k miles) and clear the codes -- then see what if anything comes back.

I can help out if you need it.

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Loren that would be fantastic. Can you recommend a place to get the sensor? I'm flying blind in that I don't even know the part that I need and I think I'm about to ask a stupid question: Do I simply ask for a Bank 2 sensor?

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Two things I forget to say: First, thank you very much for your help. Second: when I clear the codes the car run terribly, like it's not getting any gas. Then after about three minutes the CEL comes on and it runs great again. Does that add to the mystery or could it still be a sensor issue? Thanks again.

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  • Admin

986.606.126.01 Oxygen sensor (after cats) -- US MSRP $296.90

Try the folks at Sunset Imports (Porsche parts at Dealer Cost) - link at top right.

The likely reason reason it is running poorly is because the DME can not compensate the mixture for the bad O2 readings. Then it finally adjusts enough to run better but still throws the codes.

Is the CEL flashing?

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Your car has 4 O2 sensors. To see if it is a sensor or a wiring problem, you can remove the two upstream sensors and swap them, Clear codes and start it until you get aa CEL. If the fault stays on the same side, it's a wiring problem, if the fault moves, it's a bad sensor. I'd do the upstream, and after you check that swap the two downstream senors.

Based on the age and milage, You might think about buying and replacing the two upstream sensors, since they are the ones that affect the engine computer, the after cat sensors monitor cat effiiciency.

You'll need a 22mm wrench or a O2 sensor sockey to remove the sendors.

A word of caution, you will find people selling generic 4 wire O2 sensors, I've never had one work right. I tend to buy Bosch replacement, either through Sunset, or a local auto parts place.

Let us know what you find out.

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Thanks for the info, I'll order soon. The CEL is not flashing and anytime it has been on has always been solid.

986.606.126.01 Oxygen sensor (after cats) -- US MSRP $296.90

Try the folks at Sunset Imports (Porsche parts at Dealer Cost) - link at top right.

The likely reason reason it is running poorly is because the DME can not compensate the mixture for the bad O2 readings. Then it finally adjusts enough to run better but still throws the codes.

Is the CEL flashing?

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Thank you very much for the information. I think swapping them both if it proves to be a sensor problem is the way I'll go.

Your car has 4 O2 sensors. To see if it is a sensor or a wiring problem, you can remove the two upstream sensors and swap them, Clear codes and start it until you get aa CEL. If the fault stays on the same side, it's a wiring problem, if the fault moves, it's a bad sensor. I'd do the upstream, and after you check that swap the two downstream senors.

Based on the age and milage, You might think about buying and replacing the two upstream sensors, since they are the ones that affect the engine computer, the after cat sensors monitor cat effiiciency.

You'll need a 22mm wrench or a O2 sensor sockey to remove the sendors.

A word of caution, you will find people selling generic 4 wire O2 sensors, I've never had one work right. I tend to buy Bosch replacement, either through Sunset, or a local auto parts place.

Let us know what you find out.

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I have to throw a different take on this because I went through a similar problem with many of the codes you are getting. I went to two different independent Porsche certified mechanics and spent over $700 in smoke tests and diagnostics just to finally find out from an alert mechanic it was a 25 cent hose that had come undone from one of the diaphragms on the secondary air system. Along the way I was told I needed new 02 sensors, new cats, new secondary air system and etc. that would have cost upwards of $3K. Here's what I learned as it may apply to your situation. First, when you first start the car up in the morning do you hear a sound like a vacuum cleaner running, on the passenger side of the engine compartment, for about 20-30 seconds, then it goes off? If so then your secondary air pump is working. If not your secondary air pump system has a malfunction and is causing codes to appear further on up "the tree" which will cause your 02 sensors to read faulty emissions and bring up a code because your ECM has decide the car needs more or less fuel depending on what is happening before and after the cats. When the 02 sensor codes come up everyone tells you to replace them and guess what? You continue to get the codes because the secondary air system malfunction is still malfunctioning. So if it is check two places, the first is a small rubber bellows connection at the secondary air system vacuum tank. Being rubber and costing all of $1.80 it wears out and you now have a vacuum leak that causes the entire emissions system to malfunction. Check the vacuum tank as it is plastic and hardens from heat over the years and can crack. If none of those apply then check all the small vacuum lines coming from the secondary air pump especially the one under the intake manifold (this was where my problem was but only one mechanic out of three thought to look there). Typically having a smoke test done will find vacuum leaks and, compared to replacing items at random, is relatively inexpensive way to start.

If your secondary air system is working then you have another issue and Porsche has what they call "a tree" of diagnostic that is followed to hunt down these kinds of issues. I would find a good independent mechanic that is Porsche trained and highly recommended and consult with them. Indys are typically less expensive than dealers, less under pressure to get things done in a hurry, will sometimes do a free diagnostic and are invaluable in the long run.

I hope this helps and saves you some of the frustration, and money, I went through to fix a minor item that caused major problems.

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I also have a different take on this subject and can almost gaurantee, after having smoke tested for vacuum leaks,

if that passes and still there, it would be the MAF, Maf's rarely throw codes, it is usually fuel trim problems, by the way what are you're fuel trim values, those are by far the most tell tales of what is going on in the breathing process of your engine, there should be a Short Term Fuel Trim which is what is happening now and a long term fuel trim which happens over time.

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I see you're values are in the 30 percent range to the positive adding fuel, the computer can only compensate for so much and the sensors too, you need a MAF your engine is running very lean, also look at your air filter, if it is a K&N get rid of it and go stock.

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Fuel trim's goal is to maintain the stoichimetric (14:1:1 ) Air/fuel ratio, it is important to also consider the computer factors in other sensors info to move that optimum ratio about a little or a lot, 30% is a lot from what it is striving for at zero, I have replaced many faulty MAF sensors on this model porsche over the years and it has corrected the problem, but the motor should be smoke tested properly cause there are a variety of places for air leaks and that is what causes a lean problem usually...air leaks after the metered air, that are not accountable for the computer to compensate for, so this is really important to have checked by aq competant person, let me know where you live and I will hook you up with a competant person, I belong to many professional european car organizations and have friends in this biz all over the world.

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Will a smoke test reveal leaks on the secondary air injection system? Is there some kind of control valve that isolates the air injection vacuum plumbing from the manifold until the DME signals the air pump to run? I've had a smoke test run on my car without showing any leaks there but nothing special was done to enable the air injection while the test was going on.

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Will a smoke test reveal leaks on the secondary air injection system? Is there some kind of control valve that isolates the air injection vacuum plumbing from the manifold until the DME signals the air pump to run? I've had a smoke test run on my car without showing any leaks there but nothing special was done to enable the air injection while the test was going on.

The car would most likely have to be left at the shop, that is doing the test, as the secondary air system, to my knowledge, comes on the first time the car is started to pump air into the cats so exhaust gases are minimized for pollution control. A smoke test would then see a vacuum leak in the secondary air system and if it is around the vacuum tank would detect one even after the secondary air system shuts off as the vacuum tank is supposed to keep a vacuum. There might also be a way to bypass the shut off for the secondary air system to keep it running but I can't verify that. The secondary air system also has three or four diaphragms connected by small hoses and the diaphragms can be made to open and close, without the SAS operating, so they can be checked. In my case the mechanic was doing a visual check of the secondary air system and had to remove the intake manifold to get to one of the diaphragms and spotted the disconnected vacuum line.

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Wow that's a lot of info to digest and I really want to thank everyone for taking the time to write out such great information. When I start the car I do hear the vacuum cleaner sound. I wish I hadn't as that certainly would have made things easier. This is what I figured I would attempt (in this order) and check each time to see if that addressed the issue.

1. Check for vacuum leaks (somehow beyond a visual inspection)

2. Replace the sensors

3. Check for electrical problems

4. Raid my kids college fund or win the lottery

Thank you everyone. Loren, I'm traveling for the next month or so but when I get back I'll gladly take you up on your offer of assistance, thank you.

All my best,

Gabriel

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Wow that's a lot of info to digest and I really want to thank everyone for taking the time to write out such great information. When I start the car I do hear the vacuum cleaner sound. I wish I hadn't as that certainly would have made things easier. This is what I figured I would attempt (in this order) and check each time to see if that addressed the issue.

1. Check for vacuum leaks (somehow beyond a visual inspection)

2. Replace the sensors

3. Check for electrical problems

4. Raid my kids college fund or win the lottery

Thank you everyone. Loren, I'm traveling for the next month or so but when I get back I'll gladly take you up on your offer of assistance, thank you.

All my best,

Gabriel

Please come back and tell us what the problem was.

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  • 2 years later...

I recently had all 4 o2 sensor codes come on all at once. The car still ran fine and mileage was good 28 on freeway so knowing that it is virtually impossible for all to go bad at same time I looked into cleaning MAF sensor. I pulled it out, cleaned with MAF cleaner, inspected and noticed some discoloration on the metal sensor that I couldn't get off with the cleaner. I inspected some more and under the right light conditions I also notice some pitting in the metal coating. I ran about a half a can of cleaner through it trying to clear the discoloration but to no luck. After putting sensor back in, the car ran bad and misfired. I ordered a new MAF sensor, installed and the car ran better than ever. Since I owned the car at 5000 rpm the engine started to cut out a little bit. I thought it might be some limiting setting since I was approaching redline but since I replaced the MAF there is no more cut out at 5000 rpm and wow that makes it so much more powerful.

I thought that might help someone out there

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