Advice for CEL codes P1128 & P1130
 

I have a code reader and a list of the definitions for these codes from three different sources. Typically I've seen advice that these CEL codes are probably a bad or dirty MAF. But my question is, why does the actual code definition say it involves my O2 sensors? Should I replace all four of my O2 sensors? I hear they are about $130 a piece.

I cleaned my MAF today what are the chances that will take care of my CEL problem?

Engine bay & dirty air filter
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The MAF. You need a T-20 Torx Security tip (Tamper proof) to remove the two screws.
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Hole where the MAF used to be.
http://i32.tinypic.com/9arf5w.jpg

The MAF. This thing cost $250 online $400+ from the dealer! I sprayed electronic parts cleaner on the contact points. The paper clip looking thing.
http://i25.tinypic.com/2rh3h1d.jpg

The O2 sensors are just reporting the symptoms of the problem. Since they are the last sensor, there is so much upstream that could result in a O2 code. Cleaning the MAF may work, but if it doesn't, look for vacuum leaks. A vacuum leak could cause a rich condition. In addition to checking the usual tubing around the motor, check the oil cap, oil filler tube and oil dip stick. If that doesn't work, get a new MAF. Keep in mind there are 2 versions. It could be the air/oil separator, too. It's doubtful both O2 sensors went bad at the same time, but stranger things have happened--I recently replaced my O2 sensors and one replacement was bad from day 1 and it took forever to figure that out. Or take it to a shop and have them diagnose. These kinds of problems can take a ton of time to figure out without the proper diagnostic tools.

Thanks Heyjae, all good advice but please don't make me open up that mid-engine compartment again to look for the vacuum leak. I had read somewhere that if one O2 sensor goes bad it's best to change them all at the same time. I think the reasoning was that whatever fouled the first one probably messed up the others too or the new one will be more sensitive than the older ones and this could cause more CEL problems. My car is 8 years old but I only have 39,000 and change miles on it. Do you think some of the rubber could still have deteriorated just from age? I know the answer to that is probably, but I don't want to hear that. Weather sucks here today so I haven't test driven the car yet to see if my cleaned MAF and new air filter worked.

Heyjay:
How about posting a few pictures of the Boxster, in your signature it reads like it must be on mean Box.

Can someone explain exactly what happens with a dirty MAF?

HeyJae, specifically which of all these rubber tubes are vacuum lines? Which ones should I check?

The codes 1128 & 1130 are for each individual bank running lean, or that the ECU cannot control the mixture properly, (1128 is for 1-3.., 1130 is for 4-6.. or something like that..).

The fact that the code descriptions say "O2 sensors.." is not representative of the total number of conditions that need to be met to set the codes. The codes are an indicator of the affected system, not for an individual component. It is still up to the technician to properly diagnose the problem, and repair...

I had the same codes poping up on my 2000 boxster for about 8 months.. I used to be a mechanic for Porsche untill 2000 when I got my degree in electrical engineering, so now that I sit on my arse & play with electronics all day, I really didn't want to tinker with the car. So, out of lazy-ness, I tried the first thing that seemed to make sense, clean the MAF & drive it around fer a week or two.. that fixed my problem... its been a year and no CEL...

So, from my expierience, clean the MAF.. & drive...

if the code resets, well then you gotta start testing the system...

Start with the obvious first, vacuum leaks. check the plastic plenum real good, I have seen a few split or crack & cause a temperature sensitive leak..

since both codes set, what ever it is, it is common to both banks.. (on this alone you can rule out the O2 sensors..)

Thank you Skip, I really appreciate the advice. I did clean the MAF and installed a new air filter. Then the weather turned really crappy and I have not had a chance yet to test drive it. Tomorrow should be my first opportunity.

I'm a little worried that maybe it wasn't the MAF only because the MAF looked clean at least with the naked eye. But I did clean it with the electronic parts cleaner so I hope that does it.

It funny how the PCA.org site can be inconsistent with their Tech advice. I saw one Q&A answer dated 2004 where the Tech said never clean a MAF that will not fix a dirty MAF. Then in 2006 the same Tech answered the could my MAF be bad question with "try to clean it first with electronic parts cleaner, that that often fixes the problem."

They also told me No 19" wheels they will rub your wheel well liners through. And again, the folks here with 19" wheels and the same year Box as mine disproved that advice.

I'm gald I have you all as a check & balance. Thanks!

For what it's worth, here's my experience with cleaning the MAF after I got codes P1123 & P1125 last year :

http://986forum.com/forums/showthread.php?t=11810

P1123 Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Lean Threshold

P1125 Oxygen Sensing Adaptation Area 1 (Cylinders 4 - 6) - Lean Threshold


P1128 Oxygen Sensing Adaptation Area 2 (Cylinders 1 - 3) - Rich Threshold

P1130 Oxygen Sensing Adaptation Area 2 (Cylinders 4 - 6) - Rich Threshold


Nick

And what was the end result? Did cleaning the MAF in your case fix the problem?

So far, so good ( now watch, I'll bet the CEL lights up on the way home :eek: )

Nick

It's unlikely that the O2 sensors are at fault here. I've read conflicting accounts about changing just the bad O2 sensor versus changing all of them. Personally, I changed all of mine, but my car has 80,000 miles and they'd be getting close to being replaced anyway and because I changed all of them with generic O2 sensors and I wanted to keep all of them from the same brand. Of course, one of the 4 I got was bad and I needed to replace it right away and bought a different type. It seems to work pretty well so far.

Looking for a vacuum leak and/or troubleshooting codes is a PITA. After checking the low hanging fruit (cleaning the MAF--maybe replacing it, doing a visual on the vacuum tubes, oil filler tube, checking the oil cap), either take the car to a competent shop or invest in some diagnostic tools and resign yourself to spending hours learning and a lot of trial and error. The basic ones to look at are the 2 small plastic tubes coming out of the rubber coupling between manifold and intake plenum/resonator. There's one on each side. I thing the one on the passenger side is visible from the top and the one on the driver side is visible from the bottom. Then there are the rubber tubes coming from the throttle body. But a vacuum leak can be from the air oil separator (maybe), the secondary air injection system (less likely) or even the brake booster (not likely). Unless you are pretty handy, I'd defer troubleshooting those to a mechanic. There's also using propane to check for leaks. Others seem to do it fine, but I've only tried that once and was not successful with that method.

As far as a visual of the MAF before cleaning, it's probably a thin layer of oil or dirt that's causing the problem and it'd be hard to see. If you have a code reader that shows intake flow, mine is about 4-5 grams/sec. Another thing to check is your short term fuel trims. It should be within +/- 10% normally at idle, although it can be as high as +/- 25%. With the code you are throwing, yours is probably +25%. When my MAF was going bad, at idle the flow would jump around and the STFT would be erratic as well, but that's just one data point.

Hey HeyJae, thank you for taking the trouble to write such an extensive response. But this is a little over my head though in terms or seeing the values for the MAF /Intake.

My code reader is very basic. All it said was P1128 & P1130. This was with the ignition on and the engine not running. There is another function on it where you do a "MIL" reading and it says for that you have the engine running. But even if I then saw these various values I wouldn't know what to do with them.

I had these same codes about 6 months ago I tried the MAF cleaning first.....to no avail then I tried something really stupid.....atleast I thought......I bought a new oil cap......FIXED!

My theory on how the MAF sensor cleaning cures the code 1128 & 1130 is pretty simple.. the element,( the paper clip lookin' thingy..), sits in the intake air flow..

the MAF sensor is an accurate current source device in its simplist terms.. the sensor sends a current through the element which generates heat.. now as air flows over the element, it removes heat from the element which causes an increase in current to maintain the element temperature.. more air = more current..

The ECM uses the current measurement to calculate the air flow into the engine.

What I think happens to the MAF is it gets a coating of dirt, the contaminate acts as an insulator.. once it gets thick enough, it skews the airflow measurement, in other words, the element does not see all the airflow.. the result is a reading of lower airflow reaching the ECM, which injects a less fuel than actually needed.. thus runs lean...

just an engineering guess....

hahaha... yep.. instant karma is a bish...

Great explanation. But my codes P1128 & P1130 indicate a overly Rich fuel condition.

Skip is right. You are running lean with 1128,1130 codes.

Maybe it's just poor translation from German to English but the description of these codes tells us the O2 sensors have detected a lean condition and the DME is trimming the mixture to add more fuel but has reached it's trimming limit (rich threshold). The wording is lousy but that is what it means. Bad MAF or vacuum leak are the most common causes when both right and left bank are affected.

If you have an oil cap that ends with a 1 than they were very prone to bad sealing if this is the case go to the dealer and pick up a newer one it should end with a 2 or a 3 I woul;d try this before fooling with anything else since its like a $20 fix and 30 seconds of your time, my dad has the same care and had the same problem as well

Wait a minute! Are we all barking up the wrong tree here? You have a 2000 MY 986 S? If so you have a 7.2 DME. Those fault codes are different. 1128, 1130 refer to O2 sensing idle range. This would rule out the MAF as the problem. Go to Renntech.org and search these codes for your specific car year and model. Sounds like a vacuum leak is more likely. Here is one thread for the same model range car: http://www.renntech.org/forums/index.php?showtopic=18257&hl=1128+1130+codes

this is the case for these code definitions.. the translation is usually done a few ways:

1. germans who don't speak english too well..
2. americans who don't speak german too well..
3. or translators who know nothing about the context of the document...

all of which equal a loss of information.. sucks for sure...

I was workin' at a Techart place when the boxsters came out.. I was the only american there, and these guys had relatives that worked for Porsche. Needless to say, we got our hands on all the boxster manuals from Porsche.. all in german..

good thing I speak german.. the untranslated books were better than anything we could get in english back then..