Advice requested for how to handle my 1st P0133 slow response O2 sensor on a '97 2.7L

My first post on this forum so please guide me if/when I err.

Kid's 4 cylinder Toyota 2.7L 1997 4Runner 2WD with 133K miles triggered an SES today.
My code reader indicates P0133 only.
Googling implicates "Oxygen Sensor Circuit Slow Response (Bank 1, Sensor 1)"
A description appears to be:

The original oxygen sensors were never replaced to our knowledge. We have a small oil leak coming either from the oil pan or oil filter bracket mating surfaces to the engine.

We have the factory shop manual and the Chilton manual - but we have never worked on an oxygen sensor so we ask advice before we tackle this job.

Q1: Do you think an oil leak at the locations above can contaminate an 02 sensor?
Q2: Do you generally remove them in pairs?
Q3: Any other advice for diagnostic tests?

Note: We will continue googling - so this is one step in our quest.



EDIT:
Found section 4-9 in the Chilton manual which explained oxygen sensor behavior; they mentioned a "backprobe" for voltage, which I assume is we nick the wire insulation somehow. Any advice on how to "backprobe".

Also we looked on the passenger side for the oxygen sensor and wire. Maybe it's under the shield? Do these pictures show it to you?

 

I had the same callout. Replaced both sensors but it turned out to be the egr solenoid. (I think). My mechanic buddy did it because it was kicking my butt after I had replaced both sensors.

 

I dont have any input on your question, but damn! Your engine is clean - particularly your valve cover. Do you do anything in particular to clean your engine bay?

 

I would start with taking some measurements to see if the sensors are in spec still. Backprobing is when you take a meter lead and stick it in the back of the connector. They also make little prongs that you can push past the weather tight seals and they stay in place. This makes it easy for quick reading while you are diagnosing.
As for the EGR valve being bad and throwing an o2 code, not possible. They are different circuits and unrelated to each other. O2 sensors merely measure your air/fuel mixture. An EGR recirculates exhaust gases for emissions stuff. At least I don't think it it possible and I have never seen a bad EGR come up with a o2 code. o2's do go bad though. The computer wants it to read and fluctuate faster to keep a more consistent a/f mix. If it is slow to do this then the computer may go into closed loop all the time and run off base parameters. This will cause loss of mpg's.

To Moco,
If you want to degrease your engine bay of grime, use oven cleaner. Just spray it on all the greasy spots. Let it sit for a few min and wash it off.

 

As I had mentioned in the OP, there is an oil leak of the oil pan or oil filter bracket mating surface to the engine - so - I had used gunk on the engine about a month or so ago.

Exactly what I plan on doing (as I don't just throw parts at a problem) - so the question is what measurements & how.

Googling, I find the attached 500-page Toyota 3RXZ-FE diagnostic manual and also, surprisingly, an o2 sensor diagnostic sequence at Autozone.

Ah good. I was afraid I'd have to puncture the insulation. I have a good DMM so now I just have to read up a bit more on how to test the forward oxygen sensor in situ.

I found this Ehow DIY (sans photos, unfortunately):
- How to Replace an O2 Sensor on a 1997 Toyota 4Runner

Where do you guys normally get your electronic sensors from?
Is this a dealer-only part, or can the Denso online guys source it for me?

 

Trying again (the last post said it awaited moderator approval ... dunno why.)

Looking in the Toyota FSM (page SF-36), all it says is the resistance should be 11 ohms to 16 ohms between the connector pins +B and HT, so I'll need to do some more research for values.

I crawled under and found the sensor to be very easy to access - but I couldn't figure out how to disconnect the diabolical harness connector. It had one "ear" clip that I pressed - but there must be another one holding the connector in place.

 

Wow. At the $213 the dealer wants or the prices below at Autozone, it's darn expensive to replace BOTH without testing them first.

The Chilton manual has a test procedure to run where I can backprobe to test the voltage fluctuations, so that's the next step - although I was surprised that clearing the codes and driving a bit less than 100 miles didn't trigger even a pending code return. Hmmmm???

Anyway, the prices seem to be around $90 to $110 (for Denso) at Autozone but I wonder HOW to choose between the various options? Any suggestions as to how to pick oxygen sensors?



EDIT: I called Autozone and they told me the cheaper ones are the "universal" oxygen sensors (both Bosch & Denso) where you have to splice the wires yourself.

 

get o2 bung spacers. 14 dollar fix. getting to much air flow. IMO

 

I must admit I had to look up the bung spacers.
Apparently they physically move the oxygen sensor further away from the exhaust flow.
But they seem to mostly be for P0420 & P0120 DTC codes, from my quick search, not P0133.

 

The "bungs" mentioned are used to move the O2 sensor out of the flow of exhaust. This simply fools the post-cat O2 sensors into believing the catalytic converter is working properly. While this does reduce the chances of a P0420 from returning, it would not fix the problem. It simply masks it.

If you were to use those bungs on the pre-cat sensor(s), you would most likely result in creating a code, instead of eliminating it. Moving the AF sensor out of the exhaust stream will make the sensor read no changes, and the computer expects to see a steady fluctuation of the signal. (hence the P0133 code for a slow response)

A bad EGR valve can cause a p0133 code however, because if it leaks, it allows recirculation of the exhaust gases when the computer is not wanting, nor expecting it. This can cause a flat signal of the AF sensor, and a resulting P0133. If you have a scanner that can give you basic data, you should be able to observe the AF sensor data, as well as fuel trim data, to see if you have a problem elsewhere, that is triggering the code. Fuel trim codes on a Toyota do not occur until close to 25% in change, so if you were running lean, or rich, you would not get a fuel trim code unless it was severe enough to take it past the 25% range. So look at all of the data. AF sensor, fuel trim (both long and short term), EGR command, etc. If the code is a history code, and is not a result of EGR or fuel trim issues, then you may be able to go to your local parts place and purchase O2 sensor cleaner, and just remove and clean the sensor. Considering the cost of a replacement, a $5.00 can of cleaner to at least TRY to resolve the problem is not a bad idea. Again though, check the data first and see if the code is a failure, or the result of another problem.

 

Thank you very much for the additional explanation - as the entire bung idea was wholly new to me.

As you intimated, I'd rather identify and fix the problem than try to beat it with the bungs.

Thanks for the good idea and the rationale behind it (which is just as important).

Unfortunately, the scanner I have doesn't do freeze frame so I need a better scanner to obtain that data. I always wondered if it was useful - and - apparently - in this case - it would be useful to have.

Interesting. I had not realized that an oxygen sensor 'could' be cleaned. But it makes sense if getting dirty is the reason for a failure - then cleaning it should work.

Googling, this "ehow" (yeah, I know) article says you can clean an o2 sensor in gasoline overnight.
http://www.ehow.com/how_4797809_clean-oxygen-sensors.html

However, this discussion goes into how the "baked carbon" is what you really need to solubilize:
http://www.ford-trucks.com/forums/6076-can-you-clean-oxygen-sensor.html

Having never before dealt with oxygen sensors, I'm just coming up to speed. At over $200 at the dealer, it makes sense to clean them - yet - at over $100 at the autoparts store, it still makes sense to try - yet- at around $60 on Amazon, it might only be worth it if I have the part already in hand, as a last-ditch effort:

 

Found s'more information about cleaning oxygen sensors here:
http://ls1tech.com/forums/conversions-hybrids/1467206-can-oxygen-sensors-cleaned.html