P1128 / P1130 / Catalyst not ready

[crwarren11]

Hi all,

Looking for some guidance here on a 2000 Boxster Tiptronic with about 120k mi.  I am intermittently getting P1128 (360) / P1130 (361) codes which will sometimes cause a CEL and also sometimes the CEL will also go away without resetting.  Durametric specifies these as idle range codes.  I know the typical reasons for these codes which I am chasing down right now.  I have a smoke tester being delivered tomorrow to investigate further if there are any vacuum leaks in the intake.  For context, I replaced the MAF about 6 months ago as I thought this could be the source.  I did the oil cap test and idle changed when I took cap off, so that leads me to believe it is not crankcase vacuum leak.  No smoke on startup and the AOS is relatively new (5ys, 10k mi on it).  Put in a new fuel pump 4yrs ago (8k mi on it).  SAI system does not appear to be an issue based on lack of codes and SAI readiness being good.  I tightened the clamps around the intake boots last weekend thinking this could be the problem, but got the CEL again this week.  I will check the air filter and throttle body this weekend for debris when I do the smoke test.

 

Getting around to my question...I went to get smog check (California) when I had no CEL for quite some time, and all readiness monitors were good except for Catalyst.  Before the CEL came on this week, I checked readiness monitors and again all were good except for catalyst.  Are there any possible correlations between these codes and the catalyst not being ready?  Does this lead you to suggest any other things that I should check?

 

I have checked the O2 sensor voltages for all sensors.  All look good except for possibly Bank 2 behind the cat...it basically follows the O2 sensor ahead of the cat.  I ordered a new O2 sensor and will replace that this weekend to see if it helps.  I am fearing that maybe that catalytic converter has gone bad due to the signal I am seeing, but I am not getting any specific catalytic converter codes and have not over the past two years of seeing this.  Fingers crossed it's just the O2 sensor, but I changed that one about 6yrs ago (only 16k mi on it since then).

 

Maybe irrelevant but I also get the occasional P0197 code for oil temperature sensor below limit.

 

Please let me know your thoughts.  Thanks!

 

Edited April 28, 2023 by crwarren11

[Loren]

– 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

[crwarren11]

Quick update...I put in the new O2 sensor behind the cat.  The old one had a fair amount of fluid on it.  It seemed like oil to me but not 100% sure.  Also, I noticed that the O2 sensor ahead of the cat was quite loose - probably two full turns out of the threaded hole, so I tightened that one down.

 

On the intake side, I removed the air filter, MAF, large intake tube, and throttle body.  As someone else had mentioned, I found some debris and a fairly large leaf on the screen ahead of the MAF.  I vacuumed all of that out of the filter area and intake tube.  I cleaned up the throttle body, but it didn't seem too dirty to me.  I put everything back together and then tried the smoke tester.  I never got any indication of smoke coming from the intake system, even after ~10-15min of smoke going in.  That said, I am questioning the location where I was putting in the smoke.  I used the hole where the SAI hose goes into the right-side plenum.  Sorry, first-time smoke testing here...is this a suitable location or is somewhere else better? 

 

I have not had the chance to run the car yet other than pulling into the garage.  Hoping to get some more time to smoke test this week.  

 

[crwarren11]

Ok, finally smoke tested and had a couple of findings.  The intake tube had a leak at the location circled in red.  I repaired it with RTV silicone.  Two locations on the intake manifold, also circled in red.  I saw another post about someone having a leak at the place where the internal flap is located, so I'll look into that.  On the SAI hose, I noticed that it does not have the bulge at the end of it like the other one.  Wondering if this is the cause of that leak?

 

All back together and everything is running great.  No CEL and no codes stored at all.  All monitors are ready...except for the catalyst once again.  I will continue to drive and hope that it is just needing more drive cycles, but the voltage of the O2 sensor behind the cat on bank 2 is still not great, but maybe good enough to pass?  Not sure.  I would love to hear if anyone thinks this less-than-ideal voltage on the O2 sensor is what is causing the monitor to not be ready, even without any of the typical codes for cats going bad.

 

 

[mikefocke]

Maybe cite the way you are measuring the voltage and the resultant number?

 

Here are parts of a writeup by Brett on how the post cat is supposed to work that I found years back.:

 

Now an oxygen sensor outputs a voltage between 0 and about 1 V depending on the difference between the amount of oxygen in the exhaust and the amount of oxygen in normal air. If there is a lot of oxygen in the exhaust (lean mixture condition), the sensor outputs close to 0 volts. Conversely, if there is no oxygen in the mixture (rich condition), then the output is close to 1 V.

 

The post-cat O2 sensors are identical to the pre-cat O2 sensors (same voltage outputs). They are there only to monitor the performance of the catalytic converters. So, as discussed, the pre-cat sensor signals are oscillating between 0.2-0.8 volts. Once the exhaust gasses pass through the catalytic converter, most (all, in theory) excess fuel (hydrocarbons) will be combusted thus reducing hydrocarbon emissions. The cat uses oxygen in the exhaust to combust the fuel. So what you end up with in the exhaust after passing through the cat is a gas mixture that is reduced in hydrocarbons and reduced in oxygen relative to the mixture entering the cat. The post-cat exhaust gas mixture should be CONSTANTLY low in oxygen if the cat is doing its job of burning excess fuel. Therefore, the post-cat O2 sensor signal should be a constant lower voltage reading (not oscillating). So, if the post-cat O2 sensor is seen to oscillate just like the pre-cat O2 sensor, that means that the post-cat sensor is seeing the same gas mixture as the pre-cat sensor meaning that the catalytic converter isn't doing its job of burning excess fuel. The computer monitors the post-cat sensor and compares it to the pre-cat sensor. If the signals are similar, it assumes the cat is bad.

[crwarren11]

I typically use Durametric to read the values, but happened to have a wireless reader plugged in today so I can show you the readings.  As you will see, Bank 1 looks good, O2 sensor after cat is steady (green line).  Bank 2 O2 sensor after cat (green line) is oscillating, not as much as pre-cat (red line), but certainly less than ideal.

 

[JFP in PA]

[crwarren11]

Thanks. It is still confusing me why, if the cat is bad, that I am not getting the associated code. Just that the monitor is not ready. 

[JFP in PA]

Eventually it will code, it takes several driving cycles for that to happen.  If you are concerned, you can swap the post cat O2 sensors, if you get the same readings on the sensor that were working fine on the other side when they are moved to the suspect side, it has to be the cat.

[Silver_TT]

Because it's bad but not THAT bad yet.  Look at page 2 of this post:

 

 

Bank 1 = toast .... Bank 2 = not far behind

[crwarren11]

Thanks for the help guys. I suspect bank 2 cat is bad. I just wish that it was good enough to give me a ready state to pass smog. Not quite ready to give up hope but getting there. 

[Silver_TT]

Yes, those signals really tell you everything you need to know when coupled with the OBD diagnostic guidance provided by JFP.  Problem is readiness states can take quite a number of miles driving on these cars.  Maybe you could find a used set of cats, which is what I did.  Possibly from a low mileage wreck, etc.......

[crwarren11]

Yep I am hoping to find some lightly used cats. I did a couple of quick searches without much luck but didn’t put a lot of time into it yet. 

[mikefocke]

With the number stolen for their precious metals, are there many left on wrecks?

[Silver_TT]

Not sure, call LA dismantlers and see what they have to say.  It has been a long time ago but back then I think I sold the used cats to a scrap yard for around $200 and bought used cats from a forum member for around $500.  New ones were around $2K at the time.  Certainly metals prices fluctuate it will flow through to the parts price.

 

It can be hit or miss, if you buy from some random scrap yard you won't really know much about them.  That being said though mine were bad because the honeycomb had broken (something you could physically verify) I suspect due to sustained vibration.

[crwarren11]

This is probably why I didn’t see many on a quick search. I’ll get into it more as I have time to really dig. 

[JFP in PA]

In some states, due to cat thefts, is has become a legal issue to buy or sell "used" cats..............

[crwarren11]

Ahh likely the case here in CA.  I know theft of cats are a big problem here.  There are zero listings on Craigslist. Interesting that the entire x-pipe including cats are really easy to find for my M3. 
 

[JFP in PA]

It doesn't help that some of these cars are relatively low production numbers to begin with, meaning few bits get to the bone yard....................

[Silver_TT]

It wasn't easy for me but luck was on my side that another forum member happened to be selling them and they were an exact match.

 

I see some on FleaBay.... 😬

 

You always have the option to go OE and get a discount from Sunset Porsche but ya it will make your wallet easier to sit on as JFP would say.  You could also get aftermarket cats but they are a PITA with emissions and can make your ECU code and all sorts of other nonsense.

[crwarren11]

Agreed. I have a few more things to try before succumbing to new or used cats but definitely on the radar. 

[crwarren11]

Some good news to report. Monitor went ready yesterday and passed smog. I know I’ll still need to deal with that cat at some point but I’ve got a couple of years now to look for a replacement.