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Secondary Air Test Readiness monitor incomplete with O2 voltage graph

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Hi all,


I've been lurking the forum and have been struggling with some CEL codes with my 2000 Boxster S.

A little history that I have been battling with P1126 and P1133 ever since changing out the two pre-cat O2 sensors.

Then I went ahead and replaced it with a MAF and the car has been code-free for two weeks.


Now the problem is that the SAI monitor is still showing incomplete and I've done numerous cold starts.

I've read many posts in regards to this issue and saw what the "passing" graph looks like from here http://www.renntech.org/forums/topic/49155-secondary-air-test-readiness-monitor-incomplete/?p=272478


Couldn't figure why the SAI monitor never became ready status, I finally got a BT OBD2 reader. This morning, I took some reading of the voltage from the O2 sensors on a cold start.


Could someone here look at a graph and shed some light to my problem?

Should the magenta (B2S2) voltage matches the green (B1S1) sensor? Anything else looks wrong in the graph?



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The plots look strange. They should all start at 0.44v at the beginning when the engine is off/just started. Make sure you capture the log at the very beginning of cranking. The first 2 minutes is the most critical.

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Btw, I am using Torque Pro for logging.
Ok, looks like I accidentally messed up the plot when I switched to # of data points. This looks like the graph after ~10s of a start, are they all suppose to go down near 0?

I'll gather 1 more plot tonight.

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Excellent plots but it looks quite normal to me so I don't understand why the SAI readiness is not set. Perhaps drive it a few more wks and recheck?

Re the postcat reading. You can log the same sensors at idle but with a fully warmed engine instead. The post cat reading should hover around 0.7v if the cat is healthy. It will mimic the precat reading if the cat is on its last leg.

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Ok, I will put more miles on it. I think I am @ ~300mi now after yesterday's fuel up.


Question, I looked at the other post, and I see that their downstream sensor B1S2 and B2S2 are pretty much flat line near the top after the upstream sensors starting to oscillating.

How come my B2S2 (green) is oscillating and not a flat line?

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Your B2S2 (green) line is more or less flat in the warmed up graph (cold start don't count), no? In general, the less efficient the cat is, the more the post-cast reading will mimic the pre-cat reading. In your warmed up graph, both of your post-cat (red and green) lines stay pretty high at 0.7v most of the time, which is perfect.

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Would I have to continue to do the full drive-cycle in the hope for this flag to turn to ready?

Also, is there any other data that I could log to see if there's any potential issue to prevent the flag to be turned?

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I think just keep driving it like normal and see. Worst case is bring it to a shop/dealer for them to force the SAI test to make it ready (if nothing is wrong with it).

Another thing to try is scan the car with Durametric to check any pending/stored codes.

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Still no luck with the monitor over the week.

I am going to borrow my friend's Durametric to check for codes.


I am slowly preparing the worst at bringing it to a shop. Researching to see which place around San Francisco.

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Ok, I won't able to get my hands with the Durametric until Thurs night.

I've never used it before, so what should I be looking for when I have it?


Also, in the interim, should I also log the these parameters as this post?



I am slowly thinking that I might still have issue with the MAF or perhaps a vacuum leak.What should be the reading for the MAF during idle / cold start?



- short term fuel trims on both banks
- long term fuel trims on both banks
- Bank 1 O2 sensor 1 voltage 
- Bank 1 O2 sensor 2 voltage
- Bank 2 O2 sensor 1 voltage
- Bank 2 O2 sensor 2 voltage
- coolant temp
- rpm

Edited by Rochan
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Here are graphs of O2 voltage and MAF after the engine is fully warmed up and idling.

Data were taken from Durametric.


I messed up on the fuel trim logging, I will gather the data tomorrow.



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These look pretty normal to me. Perhaps you can do another cold start log again just to confrim.

What are the cam deviations? Not related to SAI but it'll be good to know too as a generic scanner can't read those.

Any pendimg codes?

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Still no pending code.

Here's some graphs from cold start.

I assume those those spikes on the cold start MAF plot was you revving the engine?

The cam deviation doesn't look steady to me but that should not affect SAI readiness though. The O2 reading on both cold start and hot idle look fine to me. Fuel trims also look fine. Maybe others can comment more.


I think it's time to bring it to the dealer to force emission tests if there are no further inputs here.

Edited by Ahsai
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  • 3 weeks later...


Replaced with a new MAF and also fixed a minor air leak in the cross tube on the intake.

Drove for a week and now I have two pending codes: P1128 and P1130.


This seems a little bit dancing in circle as most of the other post about these two codes are in regards to changing the MAF. :(


Here's some new graphs, MAF, O2 and RPM.






Edited by Rochan
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