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OBDII Code P1128 ND???

LVDell
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LVDell Member

LVDell

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Posted

Just plugged in the OBDII (CEL came on) and got 1 code:

P1128 ND Oxygen Sensing Adaption Area 2 - Rich Threshold

3 questions:

1. What next (fix) now that I have this code?

2. Can I drive the car till I rememdy the problem?

3. When should I clear the CEL (before/after the fix--I am guessing it will light up again if cleared but problem not fixed)?

Thanks!

Dell

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Loren Member

Loren

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Here is is the fault code diagnosis info from the OBD II manual:

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

Fuel/air mixture is so lean that sensing has reached its rich threshold.

If DTC P1128 or P1130 (oxygen sensing at rich threshold) is stored in the memory, this means that the fuel/air mixture is too lean.

Air leaks ahead of the oxygen sensors can lead to a fault in adaptation.

1. Check exhaust system for leaks.

2. Check for air leaks in intake air system

3. Check fuel pressure.

4. Check volume supply of fuel pump.

5. Fuel injectors fouled.

Actually, I would clear the code first (before trying anything further) and see if it reproduces.

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LVDell Member

LVDell

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Best $$$ ever spent (the equivalent to 1 hr of labor at the dealer). Essentially I was able to diagnose the problem, reset the CEL and take the tool home with me! Very functional tool at that. OF course not nearlly as cool or powerful as the PST2/3 but a great investment.

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Loren Member

Loren

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You've got mail....

I hate saying "me too" ... but honestly, me too ! I'm in the same boat with P1128 and P1130. $111 at the dealer to tell me those two codes.... aagh :( !!!

Sid

Sid, both codes means you have the same problem on both sides of the engine - highly unlikely to be injectors. Those codes say you have an air leak - look for loose or disconnected hoses, bad or dirty MAF (reading the air flow wrong), loose throttle body, cracked oil filler hose or even a bad oil separator.
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jonesrussell Member

jonesrussell

Posted
Posted
Here is is the fault code diagnosis info from the OBD II manual:

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

Fuel/air mixture is so lean that sensing has reached its rich threshold.

If DTC P1128 or P1130 (oxygen sensing at rich threshold) is stored in the memory, this means that the fuel/air mixture is too lean.

Air leaks ahead of the oxygen sensors can lead to a fault in adaptation.

1. Check exhaust system for leaks.

2. Check for air leaks in intake air system

3. Check fuel pressure.

4. Check volume supply of fuel pump.

5. Fuel injectors fouled.

Actually, I would clear the code first (before trying anything further) and see if it reproduces.

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jonesrussell Member

jonesrussell

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I have an '01 C4 coupe with about 55,000 miles. I recently added an aftermarket K&N filter and airbox. About a week after the change the CEL light came on with the code P1128. I reset the code a couple of times and the code has reappeared so I'm assuming the engine management software either won't cope or I have a faulty O2 sensor or some other problem - duh.

My question is what to do. I could re-install the stock airboxand filter and see if the code goes away, change the O2 sensors, update the EM software, or look for leaks etc as proposed above. With 4 O2 sensors @ $125 each the O2 replacement could get expensive and might not solve the problem. The new airbox/filter has really boosted the perfromance and I'm planning on adding BB headers so I hate to take it off. Any guidance you could give me would be appreciated.

Russell

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Loren Member

Loren

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I have an '01 C4 coupe with about 55,000 miles. I recently added an aftermarket K&N filter and airbox. About a week after the change the CEL light came on with the code P1128. I reset the code a couple of times and the code has reappeared so I'm assuming the engine management software either won't cope or I have a faulty O2 sensor or some other problem - duh.

My question is what to do. I could re-install the stock airboxand filter and see if the code goes away, change the O2 sensors, update the EM software, or look for leaks etc as proposed above. With 4 O2 sensors @ $125 each the O2 replacement could get expensive and might not solve the problem. The new airbox/filter has really boosted the perfromance and I'm planning on adding BB headers so I hate to take it off. Any guidance you could give me would be appreciated.

Russell

There is nothing wrong with your O2 sensors - they are telling what the problem is -- they are not the problem.

Think of the O2 sensor like the smoke detector in your home. When the smoke detector goes off it is because it senses smoke - very rarely is it the cause of the smoke.

Chances are that your K&N filter was over oiled and you got an oil film on the MAF. I suggest that you remove and clean the MAF first. The procedure has been described here many times - so please do a search.

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Orient Express Member

Orient Express

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To add to the troubleshooting, the 996 intake runners and the center intake are held together with rubber bellows. Check them for tears. This is very common especially with older or higher mileage engines. Good news is that they are very easy to replace.

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