CEL 1124 and 1126

[ajirace]

:( I have a 97 Boxster with 85,000 miles that recently began displaying the CEL for codes 1124 and 1126. I had the codes read at a local parts store to help troubleshoot the issue. The car has no after market parts or modifications and the CEL does not seem to be causing any performance issues. I reset the CEL by disconnecting the battery but it came back after about 25 miles of city driving.

My understanding of this issue is that the oxygen sensors before the catalytic converters both sides are detecting an exhaust mixture that is too rich ("Above upper limit / rich mixture threshold").

Since both sides (1-3) and (4-6) are detecting the same issue I am leaning toward an air leak. I would assume if the MAF sensor was bad I would be getting another CEL code.

I read the archives here but have seen some conflicting arguments. I bought it over a year ago and have enjoyed learning the ins and outs but this has me stumped.

Can someone revisit this issue an point me in the right direction?

Thanks,

Adam

[Ryan]

I have the EXACT SAME issue that I have been "chasing" the last few months, only NOW I also have a P0102 code. (1997 BOxster with 95,000 miles) Could it JUST be the MAF is bad? My mechanic cannot find any vacuum leaks. Maybe the 02 sensors?

Edited August 15, 2005 by Ryan

[ajirace]

 

I have the EXACT SAME issue that I have been "chasing" the last few months, only NOW I also have a P0102 code. (1997 BOxster with 95,000 miles) Could it JUST be the MAF is bad? My mechanic cannot find any vacuum leaks. Maybe the 02 sensors? 

<{POST_SNAPBACK}>

 

I changed my fuel filter tonight and you wouldn't believe the crap that poured out of it. The stainless steel bowl had dirt and a oil residue. I didn't reset the CEL yet because I wanted to see how it drives before resetting the computer. Over the last week the engine doesn't seem to idle as smooth maybe it's my imagination.

The fuel filter instructions in the DIY section are good I just wish someone would explain how to safely raise a Boxster to position jack stands. If I am using a hydraulic jack on the jacking point where do I place the jack stand?

[MNBoxster]

:( ...

My understanding of this issue is that the oxygen sensors before the catalytic converters both sides are detecting an exhaust mixture that is too rich ("Above upper limit / rich mixture threshold").

Since both sides (1-3) and (4-6) are detecting the same issue I am leaning toward an air leak. I would assume if the MAF sensor was bad I would be getting another CEL code.

I read the archives here but have seen some conflicting arguments. I bought it over a year ago and have enjoyed learning the ins and outs but this has me stumped.

Can someone revisit this issue an point me in the right direction?

Thanks,

Adam

<{POST_SNAPBACK}>

Hi,

If you had any sort of air leak, you'd be exhibiting a Lean condition if the leak occurred downstream of the MAF (since it would have allocated Fuel for a lesser mass of air going to the intake).

If it occurred upstream (and the MAF was functioning properly), it would account for the additional Air Mass and allocate more Fuel.

If you had a clogged or partially clogged Fuel Filter, again less Fuel (or a Lean condition) is more likely.

This makes a faulty MAF and/or Faulty O² sensors the most likely culprits. Since it's unlikely that the O² sensors from different Banks would fail simultaneously, this makes a faulty MAF sensor the most likely possibility.

Hope this helps...

Happy Motoring!...Jim'99

[insite]

what seems to happen a lot with the MAF sensor is that as the MAF goes bad, its ability to monitor air intake at idle often remains good, while its ability at driving rpm ranges deteriorates. as the sensor begins to fail, the o2 sensors cause the dme to compensate by adjusting the long term fuel trim (lean or rich depending on the MAF error).

once the engine returns to idle, the MAF gets good readings and tries to compensate the long term fuel trim with a short term idle trim adjustment. this short term adjustment throws the CEL (car has richened or leaned the short term trim as much as possible and has reached the 'rich' or 'lean' threshold).

so, if your codes say that the rich threshold is reached, what's likely happening is that the car is running rich at speed, so the long term fuel trim is set to lean it out. once you idle the car, the MAF gets a good reading and compensates the lean long term trim with rich short term trim. bottom line: you're rich at speed and lean at idle.

to test your MAF, turn off the car and unplug the MAF. start the car (it may not idle; you might have to keep on the gass) and go for a drive. if the MAF is your issue, the car will run much better. the DME defaults to a baseline fuel map if the MAF signal disappears.

if you have an OBD II scanner, check your long term fuel trim. in your case, i'd bet $$$ that both banks are running very negative values (i.e. -12% or less) and that the short term trims are both high positive values. this would strongly indicate a bad MAF.

[ajirace]

what seems to happen a lot with the MAF sensor is that as the MAF goes bad, its ability to monitor air intake at idle often remains good, while its ability at driving rpm ranges deteriorates.  as the sensor begins to fail, the o2 sensors cause the dme to compensate by adjusting the long term fuel trim (lean or rich depending on the MAF error). 

once the engine returns to idle, the MAF gets good readings and tries to compensate the long term fuel trim with a short term idle trim adjustment.  this short term adjustment throws the CEL (car has richened or leaned the short term trim as much as possible and has reached the 'rich' or 'lean' threshold).

so, if your codes say that the rich threshold is reached, what's likely happening is that the car is running rich at speed, so the long term fuel trim is set to lean it out.  once you idle the car, the MAF gets a good reading and compensates the lean long term trim with rich short term trim.  bottom line:  you're rich at speed and lean at idle.

to test your MAF, turn off the car and unplug the MAF.  start the car (it may not idle; you might have to keep on the gass) and go for a drive.  if the MAF is your issue, the car will run much better.  the DME defaults to a baseline fuel map if the MAF signal disappears.

if you have an OBD II scanner, check your long term fuel trim.  in your case, i'd bet $$$ that both banks are running very negative values (i.e. -12% or less) and that the short term trims are both high positive values.  this would strongly indicate a bad MAF.

<{POST_SNAPBACK}>

I have driven around 175 miles in town since I changed the fuel filter which improved the engines power. But the idle is still rough at lights causing the car to vibrate a little. When I give it gas it smooths out but comes back when I let off. I haven't reset the CEL 1124 1126 because I made an appointment at Parktown Porsche here in St. Louis (Go Cards!) but now I'm debating on changing the MAF first. Diagnostics I'm told is going to run me $130 / hour until they find the problem. About a year ago the CEL went off so I took it to Greg's Auto which was recommended by a friend but 45 min. drive. They pulled the MAF, cleaned it, and reset the CEL which I respect because they could have just replaced it and charged me for a new one.

What about all the injectors being fowled is it possible? What is your feelings on injector cleaners like Lucas?

Thanks,

Adam

[insite]

go back to the guys who read the OBD II codes and get them to write down the long and short term fuel trims (almost any OBD II scanner will show these). Post the values.

[ajirace]

go back to the guys who read the OBD II codes and get them to write down the long and short term fuel trims (almost any OBD II scanner will show these).  Post the values.

<{POST_SNAPBACK}>

Ok everyone here is the scoop. I dropped the car off at Parktown Imports and they found the MAF sensor reading around 2 when it should be reading around 10. I am getting the car back today and will post any new info on these codes if they reappear. Thank you everyone for all your insight and I will continue my adventures as a weekend mechanic. Next on my list a full brake job upgrading rotos and pads.

It should be easier than replacing the canvas top which was my first project.

Adam

[avt007]

I am another victim of the 1124 and 1126 codes. After much research, I think I have a handle on it, thanks largely to threads like this. I have learned not accept any post as the gospel, since many posts on the net say these codes are because the engine is running too lean, and others say it is too rich! My thanks to insite, he has it correct. My longterm trims were -21.1% and -21.9%, with a MAF reading of between 5 and 6 g/s at idle. After removing and cleaning the MAF (dead easy, 15-20 minutes from start to finish) the MAF now reads 3 g/s (2.98-3.19) at idle, with the longterm trims after a week of driving, at -4.7% and -6.3%. So as I read it, the MAF was reading too high, thinking there was more airflow than there really was, and was scheduling additional fuel to support it. The O2 sensors were then trying to trim back the rich mixture to something more useable, causing those high negative long term fuel trims. So far so good on the CEL light, if anything changes I'll post it.

Thanks guys,

Rob