Downstream O2 sensor fault (check engine)

[Belovian]

Who said anything about not replacing a defective part? The OP said that he was going to replace parts that had not failed. There is no point in replacing working parts. How is his mileage going to improve by replacing a downstream sensor that is passive and then replacing upstream that haven't failed? That is a bit weak.

Ok, before this gets out of hand. Let's go back. First the OP (blackmax) mentioned his CEL was on with a downstream O2 sensor fault. Then Ronsta came on talking about replacing his. For some reason I thought Ronsta was the OP with the fault code. My mistake, sorry for the confusion.

However, It has been shown in my experience and in threads here and elsewhere that an O2 sensor can be "lazy" and hurt mileage without coding. Also Most if not all manufacturers recommend replacing O2 sensors at varying intervals, as part of preventative maintenance, like plugs and T-belts. I think for years the common thought was they worked, or didn't and we know see that isn't always true.

So for the confusion on my part I apologize. To the Op definitely replace the bad O2. To Ronsta If you are seeing a drop in mileage and everything else is in order, I'd replace the two upstream sensors, as they are the ones that determine A/f metering, and as I mentioned in another thread get mileage numbers before and after and report back.


Jesse

 

[ronsta]

Hey all, don't mean to thread jack but does anyone know the appropriate nomenclature for each of the O2 sensors?

Trying to determine the voltage readings from the Scan Gauge 2 and need to program it correctly according to their chart of codes here:

XGauges for ISO & VPW Vehicles : Linear Logic : Home of the ScanGauge

pre-cat O2 (a/f sensor) - e.g. (bank 1 sensor 1/ or bank 2 sensor 1) etc...
post-cat O2 -

Thanks

 

[Belovian]

Hey all, don't mean to thread jack but does anyone know the appropriate nomenclature for each of the O2 sensors?

Trying to determine the voltage readings from the Scan Gauge 2 and need to program it correctly according to their chart of codes here:

XGauges for ISO & VPW Vehicles : Linear Logic : Home of the ScanGauge

pre-cat O2 (a/f sensor) - e.g. (bank 1 sensor 1/ or bank 2 sensor 1) etc...
post-cat O2 -

Thanks

Bank 1 Sensor 1= sensor on the side with the num.1 cyl before the cat.
Bank 1 Sensor 2= sensor on the side with the num.1 cyl After the cat.
Bank 2 Sensor 1= sensor on the opposite side before the cat.
Bank 2 Sensor 2= well you get the picture....



As a side note, If you are able to read fuel trim data, that is also an indicator of trouble. If for example your long term fuel trim data is showing +10%, That means that your injecting 10% more fuel that the pre-programmed baseline. the Pcm uses an algorithm to decide how much fuel to inject, but then gets feedback from the O2 sensors to make corrections. this is done hundreds of times a second. So if an O2 sensor is faulty you would see variations in fuel trim, + or -. Fuel trim variations anywhere near 10% are a sign something is wrong.

 

[ronsta]

so since there are only 4 O2 sensors the last one should be Bank 2 Sensor 2 correct?

 

[Belovian]

so since there are only 4 O2 sensors the last one should be Bank 2 Sensor 2 correct?

Yes sir!


Jesse

 

[ronsta]

Verdict is in: change your damn O2 sensors (all 4) even if no CEL is on. Big diff in performance, more pep in my step. About the mileage it'll probably be even less now b/c i like stepping on the gas now <//=-=- big grin

I got the scan gauge 2 but dont know how to program it to show the voltage on the sensors, not that i'll have any old data to compare it to but still...

 

[2004TR4-SR5]

well stop stomping on the gas and drive normally and prove my point for me!!! All my research on o2 sensors will pay off if I'm correct!!

 

[aghutter]

Hey there, Any chance you could elaborate on "let the pcm set the readiness monitors to set?" I have a 00 SR5 I just bought, and swapped out both O2 sensors (california emissions version) using bosch sensors, and the check engine light will not go out. A local machanic told me this might happen before I did the swap. Is there anything I can do to make the light go out? the OBDs is returning P0141 and P0141 pending codes. Many thanks

 

[Belovian]

Hey there, Any chance you could elaborate on "let the pcm set the readiness monitors to set?" I have a 00 SR5 I just bought, and swapped out both O2 sensors (california emissions version) using bosch sensors, and the check engine light will not go out. A local machanic told me this might happen before I did the swap. Is there anything I can do to make the light go out? the OBDs is returning P0141 and P0141 pending codes. Many thanks

First, what engine do you have? 4 or 6?

Secondly, p0141 relates the the heater circuit on the bank 1 downstream O2 sensor. If you have replaced the correct sensor, it's possibly the circuit that leads to the sensor, However in my experience this is rare, more often it's the sensor. Did you have the very same code before the sensor replacement? get back to us and we'll go from there.

Jesse

 

[Eastcoastrunner]

i need bank 1, sensor 1. so it's before the cat, i believe on the right side (passenger side). Can anyone confirm this? also, this diagram shows 3 o2 sensors for the 4.7 v8:

 

[Sungod]

Hey there, Any chance you could elaborate on "let the pcm set the readiness monitors to set?" I have a 00 SR5 I just bought, and swapped out both O2 sensors (california emissions version) using bosch sensors, and the check engine light will not go out. A local machanic told me this might happen before I did the swap. Is there anything I can do to make the light go out? the OBDs is returning P0141 and P0141 pending codes. Many thanks

Most likely it is the Bosch sensors. Stick with Denso or OE sensors (which are Denso).

 

[Eastcoastrunner]

is bank 1 the drivers side on an 03 v8 runner? sensor 1 in the manifold?

 

[liqourish]

aren't front o2 sensors around 250$ a pop? i wouldnt replace them until they are not fuctioning anymore. o2.sensors arent the only culprit in low gas mileage. frozen brakes, fouled maf sensor, false dash reading, clog filter, a heavy foot

 

[Eastcoastrunner]

aren't front o2 sensors around 250$ a pop? i wouldnt replace them until they are not fuctioning anymore. o2.sensors arent the only culprit in low gas mileage. frozen brakes, fouled maf sensor, false dash reading, clog filter, a heavy foot

in Canada, they are. I found that Dallas toyota sells them for @$120 a pop new, OEM sensor. Great place to buy OEM parts

 

[liqourish]

in Canada, they are. I found that Dallas toyota sells them for @$120 a pop new, OEM sensor. Great place to buy OEM parts

is that trdparts4u? i get all my oem stuff from them. they are fast and cheap

 

[Eastcoastrunner]

www.toyotapartsales.com

 

[ronsta]

by the time you get a code for O2 sensors then they're really screwed, at that point you may have done damage to other parts of your vehicle (read this somewhere). When I changed mine out my mechanic said, "oh sh*$ I can't believe they're this dirty, no code either!" Before this point he swore it wasn't the O2 sensors, no way jose, it's bc i have 265/70s etc etc... after the swap he started her up, revved it and noticed a difference, he drives an '08 v6, same mpg issue but bought it used so he never knew. Now he knows.

Disclaimer: I'm not claiming (yet) that I have a significant improvement in MPGs. What I can definitely claim is throttle response and power are back. I'll need to take a long drive for the MPG test

 

[ronsta]

Amazon.com: Denso 234-9051 Oxygen Sensor (Air and Fuel Ratio Sensor): Automotive

Amazon.com: Denso 234-4260 Oxygen Sensor (Air and Fuel Ratio Sensor): Automotive

you really need to be sure of the part #s though, something about pre 2007 and after 2007, also cali emissions...