Seeking clarification on P1128/1130

[Ahsai]

Hi Loren, John, and all,

I'm confused whether these codes indicate the engine is running rich or lean. Based on Porsche DME 7.2 OBDII manual, these codes can be either "below limit" or "above limit", which indicates rich and lean, respectively. http://www.renntech.org/forums/topic/46001-996-cel-codes/?p=252692

When Durametric reports these codes, it only says 1128/1130 "Oxygen sensing adaptation idle range 1 (or range 2 in case of 1130)" but it doesn't say whether the code indicates "below limit" or " above limit".

How to tell whether these codes mean lean or rich then?

TIA

[Loren]

Usually a P1128 and/or P1130 means: that the fuel/air mixture is so lean that sensing has reached its rich threshold.

That is the DME has sensed that the mixture is too lean so it has made the mixture richer - to the point it can not increase the richness of mixture any further.

So, if the DME thinks the mixture is too lean (based on O2 sensors and MAF) -- then you have air leaking in somewhere in the intake.

Or in a few case (especially Boxsters) you could have a weak fuel pump.

[Ahsai]

Usually a P1128 and/or P1130 means: that the fuel/air mixture is so lean that sensing has reached its rich threshold.

That is the DME has sensed that the mixture is too lean so it has made the mixture richer - to the point it can not increase the richness of mixture any further.

So, if the DME thinks the mixture is too lean (based on O2 sensors and MAF) -- then you have air leaking in somewhere in the intake.

Or in a few case (especially Boxsters) you could have a weak fuel pump.

Thanks Loren. Exactly the way I understood it....until I saw this today

http://www.renntech.org/forums/index.php?app=core&module=attach&section=attach&attach_id=30353

Which says the exact opposite hence my question.

[Loren]

They did not post the second page that goes with that for DME 7.2 - there are both descriptions for "Above" and "Below" limits.

DME 5.2.2 defines it as I explained above -- so in DME 7.2 and later those faults can mean either.

The "other" requirement to look at is whether there are any other (emission) faults or pending faults.

[Ahsai]

They did not post the second page that goes with that for DME 7.2 - there are both descriptions for "Above" and "Below" limits.

DME 5.2.2 defines it as I explained above -- so in DME 7.2 and later those faults can mean either.

The "other" requirement to look at is whether there are any other (emission) faults or pending faults.

Thanks for the explanation. So for DME 7.2 and later, these codes don't really help diagnostic much if there are no other codes. Glad I asked. These could be extremely misleading for 7.2 and later. Edited April 10, 2014 by Ahsai

[JFP in PA]

They did not post the second page that goes with that for DME 7.2 - there are both descriptions for "Above" and "Below" limits.

DME 5.2.2 defines it as I explained above -- so in DME 7.2 and later those faults can mean either.

The "other" requirement to look at is whether there are any other (emission) faults or pending faults.

Thanks for the explanation. So for DME 7.2 and later, these codes don't really help diagnostic much if there are no other codes. Glad I asked. These could be extremely misleading for 7.2 and later.

I think part of the problem is that document has a 1999 date, so it may have been correct at the time. You have to be careful with check for supplements and updates.

[Ahsai]

They did not post the second page that goes with that for DME 7.2 - there are both descriptions for "Above" and "Below" limits.

DME 5.2.2 defines it as I explained above -- so in DME 7.2 and later those faults can mean either.

The "other" requirement to look at is whether there are any other (emission) faults or pending faults.

Thanks for the explanation. So for DME 7.2 and later, these codes don't really help diagnostic much if there are no other codes. Glad I asked. These could be extremely misleading for 7.2 and later.

I think part of the problem is that document has a 1999 date, so it may have been correct at the time. You have to be careful with check for supplements and updates.

Thanks John. Do you know if this "dual nature" of P1128/1130 still holds true today for DME 7.2 and 7.8?

[JFP in PA]

They did not post the second page that goes with that for DME 7.2 - there are both descriptions for "Above" and "Below" limits.

DME 5.2.2 defines it as I explained above -- so in DME 7.2 and later those faults can mean either.

The "other" requirement to look at is whether there are any other (emission) faults or pending faults.

Thanks for the explanation. So for DME 7.2 and later, these codes don't really help diagnostic much if there are no other codes. Glad I asked. These could be extremely misleading for 7.2 and later.

I think part of the problem is that document has a 1999 date, so it may have been correct at the time. You have to be careful with check for supplements and updates.

Thanks John. Do you know if this "dual nature" of P1128/1130 still holds true today for DME 7.2 and 7.8?

To my knowledge, yes. And to add to Loren's point, on the later cars you need to collect some additional data, such as fuel trims, to know where you are.

[Ahsai]

Excellent! Thanks for the info John. Learn something new everyday.