O2 Sensor CEL

infj23

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#1
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MAKE: Lexus
MODEL: ES330
YEAR: 2005
MILES: 333K
ENGINE: V-6
DESCRIBE ISSUE.... I bought this car in March, 2015. It had 258K on it at the time.
Several thousand miles after getting it, I got a CEL for Low Voltage on Bank 2 Sensor 2. I cleared the codes and some time later, it came back. I replaced the Bank 2 Sensor 2 O2 Sensor.
Many thousands of miles later, the same code came back. Cleared it and it came back again. Replaced the O2 sensor again (Bosch).
Now it is back. The code (P0157) has been coming back intermittently now for the past year. Some times, the CEL stays off for 3-5K miles after I clear the codes. Sometimes, it comes back on almost immediately. I have not been recording the instances of it coming back after a reset, but it appears to be happening slightly more frequently.
No noted decrease in fuel economy. Engine seems to run great.
Oil changes happen every 5K. I use only Top Tier gasoline and include Lucas' Upper Cyl Lubricant and Fuel Injector Cleaner with every fill-up (I buy it by the gallon).
I don't want to keep throwing O2 sensors at this car. Do I need to replace the cat? Something else I need to check?

Thanks to all!
Doc
 

billr

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#2
Unfortunately, it isn't clear to me if the "low voltage" indicated by that code is the sensor heater voltage or the sensor output voltage. Regardless, codes generally never mean to replace a specific item, they merely point to a circuit to check out. Wiring/connectors/fuses in the O2 sensor circuitry could be the problem. Even the PCM itself, although that is least likely. Does anybody have an FSM for this car, that describes the conditions that will set P0157 for it?
 
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#3
Attached is OEM trouble tree.
Not exactly a layman's troubleshoot but here it is.... let us know if it helps-
I would start with checking sensor as bosch is NOT a recommended brand --- always use Toyota parts esp sensors..
 

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infj23

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#4
Oh wow. Stoichiometric? I've never seen that word before. I think somebody made that up.
I'll try running through that list when I get some open space in my schedule.
Thanks for the info! I'll be back when I figure it out some more.
As of now, CEL has been off for 300 miles since it last lit.
 
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#5
check that sensor heater element bosch are often off on the ohm specs. The close enough one size fits many theory does not work for Toyota
 

nickb2

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#6
Ok, my lazy ass way to chime in here.
Many thousands of miles later, the same code came back. Cleared it and it came back again. Replaced the O2 sensor again (Bosch).
This comment is suspect to me.

How many miles exactly? Do you know how to check for a bad cat? A cat can fail in several ways and there are ways to diagnose that. One of the best ways is to check fuel trims.

Hint:cool:
 

nickb2

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#8
As for Stoichiometric, think of it as a ideal perfect ratio. Normally 14.7 to one. But that will vary from engine to engine. Kind of like when I am drunk. My Stoichiometric level changes cuz my turbo is not in line with my PCM.

Since canada day is over, and I had a few jack d's and nobody to share them with cuz I flushed my GF for the upteenth time, I say f it and lets talk real shyte.

Not my writing, but I wish it was cuz my jack d brain says this is the shyte.

What is fuel trim?


The amount of fuel required to operate an engine correctly depends upon the amount of air flowing into the combustion chambers. Since the driver controls airflow (load) with the accelerator pedal, the powertrain control module (PCM) can only control fuel. It uses sensors to measure or calculate airflow, consults an air/fuel ratio map in its permanent memory, then chooses the correct injector pulse width to match that airflow. That pre-programmed injector pulse will provide exactly one gram of fuel for each 14.64 grams of air (a stoichiometric air/fuel ratio), but the PCM almost always adjusts injector pulse width to provide more or less fuel than specified in the map. That adjustment is “fuel trim.”