Gunnut

I went by the local Advance Auto store today to pull and clear the code causing my CEL to come on. (98 GS4). Pulled code P0136 O2 Sensor malfunction Bank 1 Sensor 2.
Bad O2 sensor. clerk told me it is the drivers side sensor behind the Cat.
Good enough. Didn't have the part in-stock. Didn't want to lay on the ground at zero degrees outside anyway.
He told me I really ought to replace all 4 at once because the new sensor will cause the others to go bad.

Anybody heard that one before?
Price of $118 for the one that's bad.
I think I'll take my chances and only replace the bad one.

JimA

JDMsedan

Nah, he's just trying to make a sale. Anytime you have a problem with your downstream O2 sensor, that usually means that the cat converter is not doing it's job. I would carefully inspect your cat in that location for any leaks, cracks in the element, etc. Remember, the second O2 sensor is only there to monitor catalyst efficiency. When it's voltage changes beyond it's set of parameters, it will set a code, but it in no way means your O2 sensor is bad. So inspect them both very thoroughly for obvious signs of malfunction like frayed O2 sensor wiring, loose connectors, or again if you can hear something rattling in your cat housing than it's toasted. Good news is that most catalysts have a lifetime warranty.

TRD911

Wow.. I am impressed .. I do not think that there are many people that know what you do. The post cat O2 sensor does NOTHiNG for engine mapping. BUT BUT..... BUT... But.. the OBDii still keeps up with the heating resistor circuit.

I have an 00 Tundra that I have by passed the post cat O2 sensors with a circuit I designed and implemented. I am an EE so it comes naturally.. Ha ha..

So I agree with you kinda... you need to make sure the problem is with the O2 sensor and not really the CAT.. might be hard to determine but..... just pay attention to the codes.. if it says heater circuits then it IS NOT YOUR CAT....
BP

Gunnut

The code that keeps coming up is P0136.
Lifetime warranty on the cat? Even if it is the original?

JimA

jsl55

lexus does not have a liftime warranty on catalyst. replace the o2.

JDMsedan

Okay, so lexus does not offer a warranty on catalysts. P0136 looks like a 0= generic 1=air/fuel control, 3=ignition and 6= a PCM or CAN bus issue, but let's say he buys a new O2 sensor, installs it and the MIL come back on or never goes off for that matter? You can't just throw parts at a car and expect it to fix the problem. You need to find out what the cause is first and foremost. But I guess what was said earlier was totally ignored.

JDMsedan

Thanks, It's nice to be heard every once in a while. Most of the time just because I don't approach a problem by "throwing" parts at it, people just brush me off and say I don't know what I'm talking about. Nevertheless the satisfaction of watching some people waste their money afterwards is priceless though.

lxtauto

Check O2 sensor bank1 s2 for open signal or cat for gasket leak, this is normaly the problem . good L

Gunnut

FWIW, I've cleared the code twice now. Once about a month ago when it first appeared, and again this past Saturday. It has not reappeared as of yet. (Drove about 50 miles yesterday).
Interestingly enough it did not reappear the second time until I went through a car wash that had an undercarriage wash. I'm wondering if that didn't cause a short in the sensor.
When I was under the car last weekend changing the oil and doing a drain and fill on the trans I looked at the cat and sensor that is throwing the code. It did not look any worse for wear on the surface. Exhaust system was not loose. No signs of carbon at the joints.
Car ssems to run fine. I don't like having the light in my face since if it is glowing for this code I won't know if it throws another.
I'm not one to throw parts at something. I'd rather fix it right and fix it once.
JimA

19psi

what these guys are saying is correct. i do want to add, that i've very rearely seen actual wiring problems cause 02 sensor codes unless you have a mouse problem or you hit something on the road. in that case, it will be obvious.
the p0136 code suggest a bad sensor, not a cat. p0420 or p0422 is usually the code for bad cats. the best way to make sure is to monitor your 02 sensor voltages after warm up. the after cat sensors should not cycle like the pre cat sensors. they should stay steady at about .4xxV
if a post cat sensor cycles, the cat is bad. of course you would need some good diag equipment to monitor the sensors like this.

it's pretty average to need an 02 sensor after a few years and 80k+ miles.

btw, standard federal warranty on original cats is 8yrs/80k miles.

Gunnut

The consensus in talking to the wrenches in our shop is to replace the O2 sensor. (We maintain over 300 vehicles out of this one shop)
I'll do that and report back.

JimA

Gunnut

Update.
Ordered a new O2 sensor from oxygensensors.com. Installed it today. CEL off now.
JimA