lexus-is2

I've been having the cat effeciency errors for some time now. I have no exhaust leaks and I suspect it may be the cat itself. I will be replacing the wideband sensor in the coming days but if that doesnt solve the issue, instead of changing the cats which seem rather expensive I was thinking there must be a way to send the correct reading the ECU wants from the wideband o2 sensor. I did some reading and it sees that the two black wires are the heating wires that heat the o2 sensor and the other two wires are what signal is sent back from the o2 sensor. It appears that the signal that is sent back from the o2 sensor is a + and - with a slight voltage curve. But when the voltage fluctuates a lot thats when the effeciency error is reported. So I've seen peope put a resistor in series on the positive output from the o2 sensor and a capacitor in parallel across the positive and negative.

Has anyone done this or have any experience with this method that can help and advise on how to proceed with this method?

Gville350

iTrader: (10)

If installing new O2 sensors doesn't fix it, I'd try installing a set of these in conjunction with the O2s :

2013FSport

iTrader: (2)

I'm not a fan of telling the smog center my car has an issue but you could let them sniff the pipe and if the CAT's are failing, that would be more information for you to go with. How many miles on the car and has it ever had any ignition failures? Thrown P030X codes or anything like that?

lexus-is2

Problem with that is that is clearly visible that one of these are installed. Plus not sure if wire will be long enough to allow for this

189k miles (not km, but miles) 2006 model RWD. Never had ignition failures and no P030X that I can remember.

2013FSport

iTrader: (2)

Although the miles are up there, if it's not an oil burner, typically that cats would be fine. That said, it is likely the sensors. Start with new Denso's and I bet you're good to go.

MikeFig82

iTrader: (13)

I've had to change a cat out already battled the efficiency code many times for the bank 1 side. I had no leaks exhaust or anything. I just replaced the cat with a Walker brand one. It's built pretty well actually. Only time will tell on the hold up. The only problem I see is get oem gaskets for manifold to head, and manifold to Y pipe.

Depending which bank your dealing with it's not that hard of a job. The key is probably make sure you can remove the lower Y pipes bolts off. Even then cut them off, or torch them too if you can't. Replace with OEM bolts if you can as well.

Trying to do a band aid fix is useless. If the cat's clogged your just asking for trouble down the road. Again that's JM2C.

If for bank 1 you can hit all upper 6 manifold to head bolts by removing the complete air box, and some wiring. Along with also the battery, and dip stick bracket. Some 3/8 extensions, deep sockets your good.

For the bank 2 that's tricky being that you might have to remove the intermediate shaft, and what not. I had to replace my alternator a few weeks back. I've should if checked if could hit all the bolts without it in place.

lexus-is2

I replaced the downstream secondary sensors with denso ones. Are the codes supposed to disappear by themselves? I drove around quite a bit a few times but code still there. Eventually cleared it with scan tool. Took car for emissions test and they do a fast idle test between 2500 and 3000rpm and CO was reading as 0.000 and hydrocarbons were reading at 0ppm. Last year this time hydrocarbons was reading at 45ppm and the year before that it was reading over 100 but I changed Air Fuel ratio sensor between those two and it came down to 45ppm. This year I changed downstream secondary O2 sensors and ran a bottle of cataclean (a fuel additive to clean the system, that has very good results). So either the cataclean worked wonders or a combination of cataclean and new secondary O2 sensors. But the lambda reading is at 1.013. Im told a perfect lambda is supposed to be 1 on the dot. Last year lambda reading was at 1.012 Both my upstream and downstream sensors are new now.

2013FSport

iTrader: (2)

Emission codes take specific drive cycles to clear them. Think in terms of run to operating temperature (at least 20 min) and take it on the highway at sustained speeds of 45 and 55mph. Repeat 3X and the if the codes where not present, the MIL is reset.

So, as of this writing it passsed smog and is running well? Do keep in mind that clearing codes also resets the drive cycle status back to zero if am not mistaken, hence the reason one has to drive it before it is ready for testing after clearing.

lexus-is2

Yes it passed GB equivalent to a smog test where they measure CO, Hydrocarbons and Lambda at certain RPM. So after changing the wideband sensors, I drove around a bit but eventually just reset the ECU by disconnecting the battery before the smog test. It passed the smog test hydrocarbons and CO readings were at 0. After the inspection I drove at least 6 or 7 cycles at different speeds. I then made a long 300mile journey to a vacation home that took about 4.5hrs on full tank of gas. Got to my destination and all seemed to have been ok. No MIL light. Next day started up the car, plugged in scan tool to see if any pending codes, came back with no codes stored and no codes pending. The system monitors all came back as complete and the catalyst and O2 sensor monitors were showing good. So I was quite happy. By this time I had about quarter tank of fuel left. Drove for about 40mins then parked for about 3hrs then on the way back about 15-20mins in to the drive the MIL light came back on. At this time I was heading to fuel station to fill the tank as I was getting low but not low enough for the light to come on. When I stopped at fuel station, I scanned the codes and it's the same p0420

So it must be the bank 1 cat that is no longer effectively doing its job. Which side is bank 1? Is it left or right? I'm just wondering if running low on fuel plays a role in this because now that I think about it, Im always at the low end of fuel when I get the MIL. Do you know how I can do the resistor and capacitor mod to the O2 sensor to always give a good reading to the ECU so it always seems it as fine?

2013FSport

iTrader: (2)

You might want to look at your fuel trims as it could be telling you your fuel pump is failing when the tank is low. This is more common as the miles add up, as the fuel pump strainer/filter plugs and restricts flow. Do you ever have hard starts?

All references are from the drivers seat looking forward. Bank 1 is the right side. Bank 2 is the left side. You might grab an OBD Elm 327 adapter and either Torque Pro or OBD Fusion app and the Toyota Lexus PID pack. Now you can monitor catylist temps from side to side, Fuel trims and what not and see if the data makes sense.

Edit: also you can monitor HPFP and prove your theory that on 1/4 tank or less the fuel pressure drops. Cost is like maybe $35 for the OBD adapter and apps.

lexus-is2

Never had any difficult starting issues whatsoever. Always starts very nicely even on really cold days. I've never changed fuel filter, just wondering is the fuel filter a replacement item at certain interval and how hard is it to do? Will that help keep fuel flow good?

I have a ELM327 device with DashCommand app. I also have techstream. What exactly am I looking for when monitoring fuel trims? what's it meant to read etc? how does monitoring catalyst temp help?

Is the fuel pump pressure supposed to always be the same regardless of how full the tank is? and what you are saying is monitor it when tank is nearly full and monitor it again when its quarter full?

MikeFig82

iTrader: (13)

Here's some good info.

https://www.aa1car.com/library/what_is_fuel_trim.htm

2013FSport

iTrader: (2)

Thanks Mike. I've never seen anyone post IS250 fuel pressures but they are demand driven by the engine so from full tank to empty tank, it should not matter.

Cold start on the 350 HPFP seems to go to like 2400 PSI while warm cruise could be 2000 psi. Your goal would be to create and log identical situations between empty and full.

As for the fuel trims and O2 data, I'm just saying they should be the same side to side and not be beyond max levels. An example would be that both left and right STFT and LTFT mirror each other, while CAT data upstream looks good but its triggering an efficiency error, this could point to the CAT if there are no upstream leaks. Make sense?
If you download Fusion or Torque, we could assist you easier...

EDIT: Please show us the Freeze Frame data when the error occurs. This will show what the conditions were when the CEL was triggered.

2013FSport

iTrader: (2)

Here is a random sample of some data from Fusion app. Bottom left is the catalyst thermistor temp. You would want to compare sides and wave forms which for me, torque pro does easier on the wave shape from the sensors. So $15 and $10 USD purchases.


This is Fusion pulling input and output shaft speeds from the Trans.

lexus-is2

So I did some tests with what I had available with me on vacation. I had a ELM327 wifi device and the DashCommand App. It didn't seem to be fuel related after all. On the first trip or two after clearing the code, no matter how long car is running for even though the P0420 code is pending, it won't throw up a CEL, so after every start-up I was just clearing the pending code. So it does seem like it must be the cat itself. The strange thing is that sometimes I can do a few journeys and no code pending and other times it comes. I've got new Upstream and Downstrea sensors. No exhaust leak that can be detected. So only thing left to assume would be the cat itself. I will run fuel trim data in the next few days with techstream. With the DashCommand app it was not letting me see Short term and long term for individual banks, it was just short term and long term. So I assume it's combining both maybe? With dashcommand on a cold morning start the combined short term will start at about -13% but after I drove around for few hours then the short term was about +5 and long term was about +3. But I will post more accurate data from techstream. Should I get cold startup fuel trim readings and also warm engine readings?

How exactly does the ECU use the secondary wideband o2 sensor to determine correct effeciency to not throw a P0420? There are 4 wires going to the sensor, the two black ones are wires that heat the sensor from what i've read. And the other two I think are + and - output from the sensor. So I think depending on how hot the sensor gets it produces a voltage across the other 2 wires between a certain range and possibly this voltage has to be between a threshold? I've seen quite a few videos and tips of people putting resistors and a capacitor across it to smooth the output. Any ideas how I can do this?