Check engine light on, Code P1126 on 99 Boxster

[steveltx]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

[Jager]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

Have you tested your AOS? While the car is running and warmed-up remove the oil fill cap... Is the cap difficult to remove? Does the idle drop and motor almost die? If so, the AOS is bad. Also look at your gas cap seal, does it have cracks like the one in this picture?

[steveltx]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

Have you tested your AOS? While the car is running and warmed-up remove the oil fill cap... Is the cap difficult to remove? Does the idle drop and motor almost die? If so, the AOS is bad. Also look at your gas cap seal, does it have cracks like the one in this picture?

Hi,

Just checked the oil fill cap. It's easy to remove when the car was running and warmed-up. When it's removed, the idle didn't drop and the motor was running fine.

The gas cap was replaced not long ago and it's in good condition.

What else should I check? Thanks.

Steve

[infocusf8]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

It's too bad that you spent money needlessly replacing the items you replaced but they are the things that are commonly recommended to replace when emission codes come up. Have you done a search on this site by entering the code because I believe you will find a lot of information regarding what this code indicates? My recommendation is that you take the car to a mechanic who understands the Porsche diagnostic tree and has the equipment to track down the problem otherwise you will continue to "shotgun" replace parts that may not need to be replaced. I'm speaking from the experience of also needlessly spending money on parts replacement involving this code and others like it. After spending $700 the problem turned out to be a disconnected twenty five cent vacuum hose so please save yourself some grief and money and let someone who knows what they are doing fix it.

[steveltx]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

It's too bad that you spent money needlessly replacing the items you replaced but they are the things that are commonly recommended to replace when emission codes come up. Have you done a search on this site by entering the code because I believe you will find a lot of information regarding what this code indicates? My recommendation is that you take the car to a mechanic who understands the Porsche diagnostic tree and has the equipment to track down the problem otherwise you will continue to "shotgun" replace parts that may not need to be replaced. I'm speaking from the experience of also needlessly spending money on parts replacement involving this code and others like it. After spending $700 the problem turned out to be a disconnected twenty five cent vacuum hose so please save yourself some grief and money and let someone who knows what they are doing fix it.

I removed the J tube connecting the oil separator to the throttle body and I found small build up of oil. The oil separator is probably bad because oil

shouldn't get into the throttle body and into the combustion chamber.

I apprecite it so much if anyone can confirm this. Thanks.

Steve

[mikefocke]

The AOS allows fumes to enter the combustion chambers from the crankcase. But heavy oil in the intake almost always means that the AOS is no longer doing its job.

The P1126 code can be caused by:

- intake leak

- low fuel pressure

- contaminated injectors

- fuel pump failure

- exhaust leak ahead of O2 sensors

The first step in the diagnosis flow chart is to assure the integrity of the air intake ... and the AOS is a common culprit.

You will also want to clean the throttle body after you replace the AOS and its J-tube.

instructions for both are at www.pedrosgarage.com

[Dale_K]

On my car there were intake (vacuum) leaks on the oil fill tube, both at the connection near the throttle body and a split in the accordian section near the rear bulkhead, another leak on the brake booster line and finally a leak on the Tiptronic coolant control valve actuator. I'd look really closely at the oil fill tube. Wiggle it around with the motor running and see if the rpm changes or if you can hear a hissing sound. The hissing might come from the middle or front of the motor but the actual leak is near the part you're wiggling.

Look around for a garage that can perform a smoke test. That's where they inject smoke under a slight pressure into the intake system. That's how I found the leak on the brake booster pipe. My smoke test cost $75 and was well worth it. I tried spraying flamable stuff near suspicious areas but never got anywhere that way.

[steveltx]

Hi all,

Yes. Finally, I have fixed the P1126 problem. It's the bad Air Oil Separator (AOS).

The problem is not MAF. It's not Oil filler tube. There was no broken vacuum hose anywhere.

One most important thing to check is to check the J tube connected to the throttle body.

This is the easiest thing to check instead of spending a lot of money on other unnecessary repairs.

If you see oil in the connector, then the AOS is bad. The method of trying to remove the oil stick

while the engine is running didn't work.

It took me 5 hours to replace the AOS. The trick for the replacement is simply cut the AOS bellows from below and

remove the clamp from the top. Then install the screw type clamp.

Thanks for all the helps.

Steve

[Jager]

Hi all,

Yes. Finally, I have fixed the P1126 problem. It's the bad Air Oil Separator (AOS).

The problem is not MAF. It's not Oil filler tube. There was no broken vacuum hose anywhere.

One most important thing to check is to check the J tube connected to the throttle body.

This is the easiest thing to check instead of spending a lot of money on other unnecessary repairs.

If you see oil in the connector, then the AOS is bad. The method of trying to remove the oil stick

while the engine is running didn't work.

It took me 5 hours to replace the AOS. The trick for the replacement is simply cut the AOS bellows from below and

remove the clamp from the top. Then install the screw type clamp.

Thanks for all the helps.

Steve

Glad you found the problem and got it fixed.

Just to clarify, you can test the AOS by removing the oil fill cap while the engine is running, not the dipstick.

[steveltx]

Hi,

I meant the oil filler cap not the stick. Sorry typo. It's very interesting that I could easily remove the cap when the engine was running even

when the AOS was bad. I am 100 percent sure that AOS was bad because a lot of oil was detected in the J tube connected to the throttle body.

Can anybody explain this?

My Boxster is still running excellent with NO P1126 and NO CEL after 200 miles. It used to happen every 50 miles. Very consistent.

It's completely fixed. Thanks.

Steve

[steveltx]

Hi all,

Yes. Finally, I have fixed the P1126 problem. It's the bad Air Oil Separator (AOS).

The problem is not MAF. It's not Oil filler tube. There was no broken vacuum hose anywhere.

One most important thing to check is to check the J tube connected to the throttle body.

This is the easiest thing to check instead of spending a lot of money on other unnecessary repairs.

If you see oil in the connector, then the AOS is bad. The method of trying to remove the oil stick

while the engine is running didn't work.

It took me 5 hours to replace the AOS. The trick for the replacement is simply cut the AOS bellows from below and

remove the clamp from the top. Then install the screw type clamp.

Thanks for all the helps.

Steve

Glad you found the problem and got it fixed.

Just to clarify, you can test the AOS by removing the oil fill cap while the engine is running, not the dipstick.

I figured that I owe you guys an update for the problem since you have been so helpful to me.

No, the problem was not fixed, the problem returned after running for more than 300 miles. It's not the AOS.

I guess that my original AOS is good.

After struggling for a while, I started to check all the hoses around the engine. There are two big tubes on the driver side

on top of the engine that connect the intake manifold and the throttle body via the third connecting piece.

There were adjustable clamps that tighten the tubes and the clamps were not tighten enough which caused the vacuum leaks.

The problem was caused by the garage after they replaced two emission parts and they did a sloppy job putting back everything

back together. This is a BBB recommended garage and that's why I never trust the garage. When I mentioned the problem to

them, they wanted to charge me more to replace more parts. I could waste thousand of dollars more if I believe them.

After I tighten two clamps on top of the engines, the car ran more than 1000 miles so far and there was no P1126 any more.

It's that garage that caused the problem and wasted me hundreds dollars replacing AOS and MAF. The parts are probably all good.

Just to share this with you for this. Thanks.

Steve

[spongebob]

Hi,

P1126 is the only code on my 1999 Boxster. After I cleared the code, the same code always came back after driving around 50 miles.

Replaced MAF, air filter and even the O2 sensor, still didn't help.

I checked the hose at the bottom of the air oil separator and it seems is OK.

I ran out of idea. May be vacum leak somewhere? Anything else I should check?

Thanks.

Steve

Have you tested your AOS? While the car is running and warmed-up remove the oil fill cap... Is the cap difficult to remove? Does the idle drop and motor almost die? If so, the AOS is bad. Also look at your gas cap seal, does it have cracks like the one in this picture?

I do have some similar problems but mine is running lean at load and rich at idle.

Tried to remove the oil filler cap and there was a slight resistance. Engine did also run poor with the oil cap off.

Is this a sure sign of a failing AOS?

I do think that other cars ( non P) does show similar behaviour when the oil filler cap is off.

[sliderr]

I had also this problem a lots of time almost a year ! - finally I decide to replace my AOS and my Air Sensor (not sure what the English word for it is) but its where the air comes into the engine... this resolved my issues and it drives like a rocket now.. be sure to replace your AOS with the 04 model which are (apparently more reliable) ..

[RobR]

I've got the same issue with my 2000 at 91k miles. Driving me nuts. AOS is the last thing I've got to replace, as I've replaced everything else. Hopefully, the part isn't too terribly expensive, as I've already spent more FIXING this car than I paid to buy it! Love the car, but this is ridiculous. :|

[logray]

Before you go replacing the AOS, you might want to have a look at this to confirm/deny if that is the problem or not: