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Infamous 'Check Engine' light!!!

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Hi everyone Merry Christmas,

it's been three times in past several months that my check engine light came on. First time, dealer told me that my O2 sensors are going bad and cleared the codes. It came back on after several weeks. I called my dealer and scheduled an appt. but it disappeared before my scheduled appt. So i didn't take the car in. Few days later, came on again :cursing: right after i filled up the gas tank. So i tightened up the gas tank cap and it went away the next few days.

A week passed, it came back on :censored: so i went to the Autozone and borrowed the OBD II scanner and came up with these codes P1123 and P1125 which were the same codes from the very beginning at the dealership, i think ( i was in the bay with the tech). I cleared the codes. BAM!! yesterday, it came back on :angry:

Sorry guys for such long blah blah, but bare with me for a bit.

I searched the forum and found out that others were having similar problems but mostly with MAF. Some claim O2 sensors were installed but lights came back anyways.

So Loren, or anyone with similar episodes, my question is Do i bite the bullet and replace the all O2 sensors first, then MAF, then oil separator, then bellows tube, then DME, etc....

Guys! i don't know where to start, seems that dealers can't pin point the problems either. i don't want to start the process of guessing elimination at my cost either. If i go to autozone and get the same P1123 and P1125 codes again. What is my next logical step besides taking her to the dealership first? I've already checked for any leaks in any hoses near the intake. I do have cat-back B&B exhaust. Could this be one of the problems?? I don't have any intake systems of any sort.

thanks in advance for any inputs, advises


p.s. my car is a 99 C2 with 50K miles

i have no driveability issues, perfect idle, runs thru RPMs fine, runs no diff. from when the celis is on or off

Edited by elixer
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The O2 sensors are just that - sensors. They are likely not the problem but the problem reporting mechanism.

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

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

This would mean that the fuel/air mixture is so rich that sensing is up to it's lean threshold and can not lean the mixture enough.

My list of probable causes are: fuel pressure too high; fuels injector(s) leaking; EVAP canister purge valve open.

Could be the charcoal canister (which should be covered under emissions warranty) or fuel pressure too high because of dirt stuck in one of the valves or a bad fuel pressure regulator vacuum connection. In the end all of these may be covered by your emissions warranty (unless it was caused by a dirty fuel filter/fuel).

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Apparently your engine is running rich on both banks. Could be caused by a vacuum leak. Check all connection and vacuum pressure. I know you already checked it, but make sure the gas cap and seal is good and tight.

Also, you might try resetting the codes, disconnecting the MAF and seeing if the 1123 -25 codes come back on, You WILL get the CEL because of the MAF being disconnected, but you might see that the O2 sensors will adjust the air/fuel ratio correctly using the standard DME fail safe. If this happens, then you can assume that the MAF is faulty and reporting too much air flow to the computer. Try cleaning the MAF.

Let us know what happens.

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will double check on all connections and gas, oil caps tonight

thanks much on the disconnecting the MAF tip, that makes sense!!

little confused on your direction, I should clear the current codes first, then disconnect the MAF, then crank the engine and idle a bit, then read the codes again?? Is it safe to run without MAF? Sorry if it is a stupid question as i am mechanically-challenged.

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Go out and drive the car a while after you reset the codes and dsconnect the MAF. Yes it is perfectly safe to run without the MAF. The reason you are resetting the codes is to get rid of the 1123 and 1125 DTC's that are recorded in the computer. You will immediately get a CEL for the disconnected MAF, but if you don't get the 1123 and 1125 codes, it may mean that the MAF is the problem. You may still get all the eror codes back.

I would still clean the MAF and double and triple check for vacuum leaks. If any work has been done on the engine, a hose may have been dislodged. A specific connection to check is the "Y" connection way back on top of the engine on the driver's side. If you take a flashlight and look back there, you will see that one of the black plastic (very thin) vacuum lines that is connected to the "electric/vacuum" controlled changeover valve (located directly behind the alternator) is connected to a rubber "Y" union. The other 2 ends of the "Y" should be connected as follows: 1 to a vacuum canister on the left and the other to a hose that has a check valve inline. Many times I have seen the connection to the vaccum canister disconnected. This will effect the operation of the engine very slghtly, but will increase the richness of the engine.

Another way to test what is causing the error code is to partially block the air filter. By reducing the amount of air that can pass by the MAF, you are artificially recalibrating the signal the MAF send to the computer. The computer will now be told it is getting less air and therefore will reduce the injector time, allowing the O2 sensors to operate in proper range.

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hello all,

I have a 99 boxster 2.5 that had the exact same codes. There was a gas cap recall for the 99's not sure if yous falls in this category but solved the problem for me also make sure you have a good seal at the dip stick and oil cap. I also cleaned the MAF with radio shack electronics parts cleaner as this seems to be a common problem. I have put about 200+ miles with no CEL. Good Luck!!


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Thanks everyone for help

i will check off each and every items advised here

p.s. U da man, 1999Porsche911 :notworthy:

are you a mechanic??? u seemed to know our cars very well. :thumbup:

again, thanks for sharing your knowledge

i will pick your brain later for sure, time to time, hopefully not too often :cheers:

Edited by elixer
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Hi Guys,

Hope you don't mind me joinng this discussion. I have a '98 Boxster that is registering codes P1124/P1126 (Enrichment Limit) and is running very rich. I believe the MAF is the culprit, but pardon my ignorance, where is this located on the boxster? AaronHurd, if you could clue me in, I would ilke to clean this and see if it will address the problem.

Any other guidance would be appreciated. Thanks!

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