Error code P1128 so it begins...

[Lobo1186]

So i threw my P1128 out the other day. This is (drumroll)..."P1128 Oxygen Sensing Adaptation Area 2 (Cylinders 1 - 3) - Rich Threshold"

sweet. So i have done some searching on here and on renntech. And it could be a vacuum leak or a bad AOS or a bad MAF. BUT All of the threads about this usually are in conjunction with another code not just one. (usually 1128 and 1130)

does this mean it could be something other than the afore mentioned? I will do some of the simple things like check for an air leak.

[paulv]

Fault listing:

– Incorrect signal from MAF sensor
– Intake air system leaking
– Fuel pressure too low
– Volume supply of fuel pump too low
– Fuel injectors fouled
– Exhaust system leaking

Also, air leaks ahead of the oxygen sensors can lead to a fault. BTW, The P1130 is the same fault code for the other cylinder bank.

Regards,
paul...

[Lobo1186]

I have heard that one way to check AOS is to remove oil cap while engine is running. If it is hard to remove or a sucking sound it could be a failing AOS. So i tried it and it caused the car to rev or get audibly louder and there is a sucking sound. does this mean bad AOS?

- I plan to clean MAF
- Check air system for leaks
- idk what i can do about low fuel pressure
- or volume of fuel pump thing
- or how to check injectors.
- and I should be able to hear an exaust leak which i dont.


thanks for the help! ill check into these asap

[Lobo1186]

so from what I understand the sucking is a good thing. and if it didnt suck then it would be bad. (ironic) BUT it isnt a terror to remove comes right off and sucks.

also another symptom the idle is a little rough nothing extraordinary but the needle moves a little.


this makes me want to say BAD MAF but, if it was a bad MAF howcome it is only throwing the one code for cyl 1-3?

[Bladecutter]

If the MAF were bad, it would in fact affect both banks, not just one.
You might want to concentrate on the O2 sensors, and any leaks on the intake or exhaust system that might be the cause.

What I can recommend that would be reasonably easy to do, and not cost you a cent, would be to remove the O2 sensors, and switch them from the right bank to the left bank, and vice-versa.

If the fault then changes banks with the O2 sensors, then you know the issue is related to the O2 sensors, and not anything else.

If the fault then goes away, and doesn't come back, then it was probably a connector issue, and disconnecting and relocating them cleared that up.

If the problem stays on the same bank, then you are most likely looking for an intake or exhaust leak.

BC.

[JackG]

I chased a very similar problem a few months ago. My errors were on one bank only, but it turned out I had a cracked oil filler tube (vacuum leak).

If your problem turns out to be O2 sensors, I have a brand new pair for one side for sale here on this site. Bought them for mine but found out it was the filler before I ever installed them.

[geoff]

Originally Posted by Lobo1186

...
this makes me want to say BAD MAF but, if it was a bad MAF howcome it is only throwing the one code for cyl 1-3?

When my MAF went bad and turned on the CEL, the only code I got was P1128. I turned the CEL off and a few tanks of gas later the CEL came on with the same code. I never got a code for the other engine bank. I traced the problem to the MAF by cleaning it and driving for several tanks of gas without the CEL coming back. Once I knew the CEL was due to the MAF, I replaced the MAF and now have a cleaned but used old MAF as an emergency backup. Cleaning them is not the same as a new one

From talking to the lead tech at the dealer for a long time and going through all the PIWIS screens, all the various emissions parts work together to constantly adjust air and fuel flow, timing, etc. relative to temperature, pressure, emissions parameters, etc. The computer in your car will adjust timing and fuel mixture as much as possible to keep things within a set range of parameters, so if one engine bank parameters are different from the other, such as due to different aging of oxygen sensors, engine timing, or whatever, the computer might think one bank is good when the other isn't. Hence the CEL only showing the P1128 and not the P1130 codes.

[Lobo1186]

sweet geoff thanks. This weekend ill get into the ride and tinker around a bit. Like you said I can clear it and it wont return for a good 100+ miles at least right now im trying to get it to throw again get the mile gauge and then clean the maf. And I will do the 02 swap. we will see but i will let you guys know how it goes. thanks a bunch

[geetee]

Similar situation here. I've had P1125 and P1132 about 4k miles for so. Cleared it and cleaned MAF and haven't seen it since. Just recently got a P1128 code so cleaned the MAF again and haven't seen it for a few hundred miles. Only thing is I feel a loss of power 4k and up. Doesn't seem to pull as hard.
I just ordered a new MAF. We'll see how it goes. Cars got 78k miles and original MAF. 125-00 so I ordered the updated 125-01.

[Lobo1186]

I cleaned my MAF also so we will see how it goes. It looked like it had some residue on it and some dirt just a little so who knows.

[geetee]

I just replaced the MAF and the once in a while cold start rough idle is gone and car pulls all the way through the rpms. I guess it was the MAF after all.