2002 Lexus ES300

Ok here is the story on this fine ride. It's a customers car that she brought to us in late August with a 1-3-5 misfire. She had taken it to a so called specilist in the field of Lexus. So after running some test with the scanner, it was determined that the Bank 1 Sensor 1 was causing the issue with a drop in voltage of 1.4 volts and it needs to have at least 2.8 volts or better. Once we replaced the A/F sensor the voltage was up to 3.79 volts and the car ran great! About a month later her SEL came on and didnt run rough or anything. At this time we thought maybe because the Lexus guy had dumped in 4 different fuel treatments so we reset the computer and it ran great for about 2 weeks. Now its back in my shop with the SEL coming on with a 2-4-6 misfire with the following codes :

P0302,P0304,P0306
P0156,P0175,P0420

When I test the voltage on bank 2 sensor 1, the voltage jumps from 1.6 volts to 2.6 volts up to 3.29 volts making me think that the A/F sensor is bad.

After talking to the customer she told me that when she bought the car in May the SEL was on and she told the person she bought it from she wanted that fixed (private sale). HE took it to a friends shop of his and had 2 sensors replaced. I called to find out which sensors and it was an A/F and O2 sensor, they couldnt tell me which one but did say that they used a few different combinations to make the SEL go off and stay off...this was in June.

Im at wits end with this.......I can drive the car without a misfire but the VSL and Trac light come on which I had reset with the scanner before by calibrating the sensors with the snap on scanner.

Does anyone have any ideas on this....it runs great once its cold but she said once it warms up it misfires which I can get it to misfire but that darn light comes on with the above mentioned codes....any help would be greatly apprciated. Thanks!

I'd either verify the correct 02's or A/F sensor was installed or switch them to the other bank. ru sure they worked on the correct bank? If they did then I'd surmise that the converter is restrcitted on that bank and that's why it's generating misfires on that side of the engine.

Yes, I have verified that i recieved the proper parts and installed them on the banks correctly. Each bank uses a different part number. We are using bosch sensors from Advance and I looked them up myself online to verify they are correct as I used to work at an auto parts store back in the 90's. I recalibrated the sensors today with the scanner and let it idle for 2 hours and no check engine light. I know as soon as I send it back to the customer, it will start acting up again. Im starting to wonder if the MAF has anything to do with it....noticed a few of the codes like the P0175 and P0 156 point towards a MAF being bad, therefor causing the A/F sensors to jiff out. Any thoughts? Thanks

yeah that's what I mean about correct! Lots of posts all over the net about reoccuring codes with new Bosch sensors. The heater elements don't seem to heat up fast enough or stay hot enough to clear the codes. That's what i meant about correct! I'd call the dealer for the correct ones. Why would a MAf throw misfire faults on only 1 side of an engine! The MAF makes no sense to me! I mean throw a MAF at it if you want but I wouldn't waste anymore time myself until I'd used the correct 02's A/F sensors. Any idea what brand the factory ones were? NTK? Denso?

Not sure as when I took the A/F and O2's out they didnt have a name on them at all or any type of markings. I just found it strange that the one shop told me they replaced the A/F sensor and 02 sensor with different ones until they found a combination that would make the light stay off.

The reason I say about the MAF is that something somewhere is causing these A/F sensors to burn out. I find it funny i replaced one and it last a month and a half and now the opposite side (bank 2) is acting up just like the orginal problem. I also noticed the exhaust has a funny smell to it, very gassy just like when you clean out the throttle body with a can of carb cleaner.

I agree with you in the fact about throwing parts at it like a MAF but I am going crazy with this car. I've been very good at troubleshooting many cars but this one has me stumped big time. I know its got to be something very simple so therefore thats why I am thinking MAF because of the p0175code and p0156 code and I was reading that these codes could cause a misfire.....why just misfiring on bank2.....my guess is that the A/F sensor hasnt been replaced yet like I did on bank1. That along with the 4 fuel treatments that another place did on the car took an already bad A/F sensor and weakend it. I was told the A/F sensor works with the MAF but the MAF really does most of the work with the computer and the A/F's just do a bit of fine tuning. I just dont want to throw $70 at the car and have it coming back on me, but the problem has to be deeper then just a bad A/F and / or O2 sensor. If I replace this A/F sensor its like putting a band aide on it and in a month..bam its back in the shop. I refuse to let this car get the best of me!!!!

Air/fuel and O2 sensors are NOT interchangeable. Like Jeff is trying to say you need to make sure you have the CORRECT sensors installed. With the voltage you are giving the car should have A/F sensors upstream. The heater code for the downstream O2 sensors probably will have little effect on your problems short of the light. A bad or incorrect A/F sensor will cause running problems and misfires.

I don't believe anything is causing the new A/F sensors to burn out except that if they're Bosch then in my opinion they're junk. I think it's operating occasionally in a set of parameters that keeps the light off but most of the time the parameters are out but depending on drive cycles, trip counters etc the code is not always matruing. Hats off to you for wanting to beat this and I don't think you're misdiagnosing you're just doing what thousands have done before and tried to replace a properly engineered tested part with something that another manufacturer tells you should work. should being the key word, yes the shorted sensor is replaced with a non shorted sensor and in turn the drivability improves but alas the code remains because the heater element, the expensive part of the sensor to make is inefficent compared to the more expensive OE part. Even if the factory part was Bosch I'd still trust only the dealer parts dept to get me the correct, sometimes revised part. They're going by a system that constantly updates part numbers as running improvements arrive etc, they aren't just using a book or a webpage sent out free by a manufacturer that says this sensor will okay in alot of applications and not perfect in any. I trust the guys that work with them dailyt to get it right. Not knocking Advance just saying the get contracts from suppliers and that's what they had to use. The jobber I used to deal with stocked and sold only NTK and had only a few issues with them. He switched to Bosch because he could stock more applications with fewer part numbers and his retunrs increased by 75%. All this im sure isn't new to you if you used to work in the parts business, you have no doubt been there and done that. I'd hate to see you waste more time checking for cam timing issues, vaccum leaks etc, etc for one side of an engine when you've got new parts in one side that is likely causing your issue! Other websites like IATN have countless posts confirming the same experiences.

Yes, I know that A/F sensors are upstream sensors and o2's are down stream sensors and are NOT interchangable. And that all 4 sensors carry different part numbers.

As far as dealer direct parts, not knocking all dealers but we have had some bad experiances of late with dealer struts from Ford, sending used struts, 2 left struts, wrong struts packaged ect ect. I will however take your advice and call the local Lexus parts supplier and see how much the A/F sensor for the front (bank 2 sensor 1) is and let my customer know that she should try an OEM part from the dealer at the recommendation of several people I have spoken with over the last few days.

I have checked for vac leaks, timing issues, exhaust leaks ect. I guess what has me stumped the most is that I got the misfire code but not the P011XX code for the A/F sensor, Im just not satisifed with the voltage values I am recieving with it jumping around. Tested the Bosch one tonight (Bank 1 Sensor1) and it was at the 3.29volt and holding pretty steady where as the Bank 2 sensor 1 A/F sensor still is jumping voltage around from 1.6 - 2.79- 3.13 ect ect and then back down. I wanted to wait before I replaced the front A/F sensor so I could get a code on it but so far nothing. I am going to go for a long drive tomorrow and see what happens. Wish me luck!!!!!!

Sure I can understand the strut issue but that's a quality issue of the supplier to Ford. At chrysler dealerships the replacement struts are reboxed Monroe, The exhaust reboxed Walker. 2 names that im not overly impressed with there history in terms of quality. That being said there's way more R&D and testing before delivery done to the engine controls then the suspension pieces which is why in my humble profession opinion you use dealer parts for electrical and engine management parts. I mean if your customers will all pay labour twice if the cheaper parts don't work then that's a good way to stay busy when they fail but mine don't so I don't give them the option of a cheaper part that Im not 99% sure will work because I've seen the same part work in the same appliation several times prior. If you're on some on the pro tech sites like IATN you'll see tons of posts about jobber fuel pumps, crank sensors, 02 sensors, thermostats, Catalytic converters etc. Just my 2 cents