Timanator

My wife's RX300 failed a California smog check, there was/is no CEL. I've checked the pcv valve and it appeared to be working ok. I've put a code reader on but no codes were indicated. I've looked at the spark plugs and they don't look too bad. I may change them anyway. Although changing the back ones don't look like fun. The vehicle has 70k on the clock.
Looking for other suggestions.

Thanks

Tim

TunedRX300

check your MAF sensor and clean it. What part of the test you fail? CO, HC, or CO2 measured?

Lexmex

So you passed tailpipe, but how did they know the CEL was not working?

One thing you could do to trigger one is pull of the top of the air box and attempt to start the car, it should choke and throw a CEL.

docfnky

change the oil, air filter, and put in a full tank of chevron 92 octane.

Timanator

I had recently changed the oil and filter. The vehicle failed on HC and CO.
I just changed the plugs yesterday. They didn't look too bad. All of the back ones were ever so slightly darker around the metal base of the plug, the insulators looked about the same, fairly white/tan.
I will try cleaning the MAF.

Thanks.

slick20

change air filter and pcv valve and the spark plugs as the gap may have changed with ware. .have fuel injectors cleaned.you will get a more complect combustion when the cylinders fire and that leads to cleaner emissions.

Lexmex

Let me know what the actual HC and CO numbers were, as I remember that California gives them.

I would actually replace the PCV valve and look at the hose that it sits on from the engine to the throttle body to make sure that is clean, too.

TunedRX300

I don't believe 92 octane rating is avaliable in California. Can someone explains to me how higher octane gas will help?
I passed smog test three months ago and my HC is higher than average number reported. CO is way below average. I would clean MAF first, then AF Sensor, then the cat.

Timanator

The O2/AF sensors were replaced by Lexus9 months ago, CEL did light up. How would you clean them or the cat? I'm going to run some Techron injection cleaner through this tank and try a re-test next week. I may go ahead and replace the PCV valve even though it's seems OK.

Thanks for the ideas.

Tim

TunedRX300

sorry, I meant to inspect or replace the AF senor, if you have new sensors, they should not be the cause.
Unless you are using really cheap gas for 70K, I doubt Techron will help you.
Hopefully it is the cat that is bad, the cat is covered for 8 years 80K under federal emission warranty. Get your smog failure report and talk to Lexus if you still fail after cleaning MAF.

Timanator

I'll have to follow up on the cat warranty. I know that CA has a 7yr/70k emissions warranty that covered the AF sensors, although the Lexus dealer insisted that they didn't cover them. They eventually said they would cover them as a "good will" gesture. I thought that there is an O2 sensor after the cat that would set a code if the cat was bad. Anyone know if I'm on the right track here?

Thanks again,
Tim

TunedRX300

Catalytic Converter is one of the very few parts that fall under the EPA 8 years / 80,000 mile warranty.
I would go to a different Lexus dealer and bring your warranty supplement manual. I believe AF sensor is also covered and should not be even considered as a goodwill, it is a legit warranty item. The one behind the cat functions differently than the ones before. Lexmex, could you comment?

Lexmex

There are two AF sensors that come before the precats. The precats help lower emissions before the main cat has sufficiently heated up (about 3 minutes). This is readily visible on the front exhaust mainfold that comes out of the engine. I don't have precats and no CELs, part of the reason being those AF sensors come before the precats.

Now, beneath the RX, there is the main cat and just immediately after...another AF sensor.

There is an obd2 code, P0420 (Catalyst System Efficiency Below Threshold). The only three remedies listed are, replacing the cat (pre and/or main), an open or short in the AF sensor circuit or the AF sensor itself.

What occurs is that there is a wavelength before and after the main cat beneath, and if the ECM doesn't like what it sees compared to a certain performance range, it throws off a light.

rklages

Mass Air Flow Sensors (in the intake) fail quite often on RX300's, especially between 80-100k - they sometimes throw a code and sometimes they come and go and then finally fully fail and will eventually set a code. They are too expensive to just buy and try ($250 or so). In a closed loop system, either the O2 sensor is incorrect, the MAF sensor is incorrect, or they are both correct the the cat isn't doing the job. Things like the plugs and injectors generally won't have a big effect on emissions and the computer will compensate for most things like that (unless a plug is so bad that it isn't firing enough to burn fuel and the raw fuel is going into the exhaust. It is all pretty hard to backyard troubleshoot and if you don't get a code, then you need some good test equip to figure it out. Cleaning sensors can do it, but the O2 sensors are tough to get out and also pricey to buy if you break one. Good luck - if your lucky it will set a code soon.

Timanator

Well I took it for a retest this morning and it passed - baerly. It failed last time on both the 15 mph and 25 mph tests.
The limits
@15 mph are HC 50, tested 51, CO % .64 tested .89
@25 mph are HC 34, tested 69, CO % .78 tested .99

On the re-test
@15 mph are HC 50, tested 50, CO % .64 tested .21
@25 mph are HC 34, tested 08, CO % .78 tested .13

As you can see everything was improved but the 15 mph HC which improved by only 1 point and barely met the limit.

I changed the plugs, old ones didn't look too bad, cleaned the PCV and MAF. I also pulled the fuse on the PCM to reset the fuel trim.

Anyone have any ideas on why the low speed HC was so high and what I might look at next. I was thinking that I might changed the fuel filter.

Thanks again for the help and ideas.

Tim