So I had my little annoying yellow buddy pop in for a visit a few weeks ago, mocking me constantly every time I drive my truck.
My scanner reported a P0136 code, which of course is a:
Oxygen Sensor Circuit Malfunction
(Bank 1 Sensor 2)

Open or short in heated oxygen sensor circuit

Heated oxygen sensor
No big deal, I figure, the O2 is original with 131K on it. I'll just replace it. So I finally get around to ordering the new O2 sensor from Amazon yesterday. Wouldn't you know this morning I get in the truck and the check engine light doesn't light up. Just my luck, I'm thinking, $76 down the tubes.
Shortly thereafter, however, I notice that the truck had seemed to be lacking in power. The three weeks previous with the light on, the truck seemed as peppy as ever. Today, with no light she is tuned down a bit. I pulled the EFI fuse and let it sit a bit then fired her back up. Runs great again as before, and still no light. A rescan shows one trouble code still - P0136, even though no CEL.
Can anyone explain what might be going on here?
Here is what the O2 looks like as of two months ago.

 

Nobody has had this happen to them? Just wondering if I should be diagnosing any other components before the new O2 sensor arrives.

 

it is a bad sensor most likely just working a little and has not tripped the CEL in three trips as well it is sensor 2 which I believe is behind the cat PIC did not show and correct me if I am wrong... if it is behind the cat then that may be the issue

 

100k--replace both sensors and the TPS. URD sells the O2's for a steal and they are yota experts.

What happens is the computer resets after you pull the fuse.....(drives in a little safer mode). Then as you drive it starts to trim fuel and timing based on sensors.

From what i know the rear sensor does very little when it comes to the fuel trims. So it could indicate the front is getting lazy.

These trucks run at Air to Fuel ratio or 14.7 (+- .10)--BUT the most power is made at 12.3. So what I am getting at here is that maybe fuel trims are running a little lean and timing is being dialed back=less power.

The TPS also goes out about this time($40) part so just replace every 100k. My .02$

 

OK, I will look into the TPS also.
More info for you guys to chew on. Yes, this is a Cali spec truck, so it is the rear sensor. I replaced my front A/F sensor for the second time about 1,500 miles ago (130K, went out first time @ 85K), it should be fresh as a daisy. This rear sensor is the original to my knowledge- definitely due.
The thing that confused me was that the truck ran fine before yesterday even with the CEL on for three weeks. It seems very strange to me that the CEL goes out at the same time I notice a significant lack of pep.
I can understand the O2 maybe going in and out, but I would think it would throw the light when out and turn the light off when it is working?
One more data point- I noticed a bit of rough idle the moment immediately preceeding the CEL coming on a few weeks ago. Wouldn't seem to me that the O2 would cause a rough idle, but I'm not sure.
Anyway, I just made my second commute with the CEL being off and it is still off with the truck still running strong. I guess we'll see if it falls back real soon.
For the TPS is this a common problem? I thought I read that they can be cleaned?

 

hross14 is right that the rear o2 sensor does not play much part in the fuel trim at all however the front one does!!! basically the maf tells the ECM how much volume is entering the engine and the front o2 tells the ECM what the percentage of o2 is actually in the air being taken in, the rear o2 tells the ECM whether or not the cat is doing what it is supposed to or not! so this is why I mentioned the cat. if the cat is possibly any issue then you will know for sure after you replace the o2 sensor, usually the code thrown is the cat code not the o2 code however the rear o2 sensor can precede the cat in the replacement process! I hope for this is not the case!!!

So in agreement with hross14 definitly time to replace the o2's and definitely look up URD!

I would recommend seafoam at this point as well both through the intake via vacuum and through the tank!!!

 

Yep--time for a little overall R&R

here is my 100k service
**Timing belt and etc...
**AF/O2 sensors
**TPS--usually starts going around 100-150k (it cheap)
**Send injectors out to be cleaned or do it on the Truck--your choice (but sending them out--they test and measure them for you also)
**Clean and test MAF (This is what can be cleaned)
**I take off the TB and clean it--but if you are --err--lazy you can clean it while it is still on
**Check PCV and etc
**Change all oils (More or less)
**Coolant flush and change
**Belts and hoses

And last but not least--Girlfriends.

I am giving you suggestions but in reality it is hard to really diagnose a problem via internet--know what i am saying. Also--is it worth your time to spend hours testing these parts when you can get them all for about $250? Then you know you are golden.

TPS--mine was going on mine at about 150k--they get lazy and cause weird issues--hit or miss

 

250.00??????? I never!!! where do you shop???? Belts definitely, timing belt usually do water pump as well, OIL CHANGE ABSOLUTELY "including trans, and rear end, and diff!!!! Coolant flush ONLY USE Toyota Coolant, or the red stuff if you are running on the cheap side. AND NEVER USE GREEN!!!!!!!!! Green eats at aluminum and if you know any thing about your truck most of the engine and components are ALUMINUM !!!!!!

 

i was talking about replacing the sensors

 

Good list.
My TB and MAF are clean, A/F is new, O2 is on order (Amazon beats URD in price all day long). I will certainly grab a new TPS when I get near the dealer.
Fluids are good, though the coolant is possibly due. How long does the Super Long Life go? I am not planning to do the timing belt until my water pump goes. Plugs and wires are in the garage waiting for a nice day with some free time. Over the last three or four months I have SeaFoamed the intake twice, the tank twice and the case once before my last oil change.
She should be in good shape.
Anyway, I just made my third and fourth trip with the truck and the light is still off, and still running crisp. No matter, I am replacing the old O2 anyway.
TPS could be the smoking gun- I've noticed the truck idling higher when cold lately. After warmup it does go back to 650ish which is normal. I didn't recall the rpms being as high when cold (~1500) but I may be imagining that.
Totally off topic, but on my way home I found myself to be the meat in a 3rd gen sandwich I had to snap this pic. It looks like we are about to head off to do a little wheelin'. Sure is an interesting spare tire carrier on the silver one. Love the chrome bumper touch up also

 

that makes sense just the list threw me off... I agree!!!

and if you are talking about a high idle and the tps does not fix it then the temp sensor is probably culprit. or the maf but you probably cleaned that already.

 

The symptoms i got when my TPS was going was an occasional low idle---little rougher idle. It especially happend when i had the AC on....

Search it though and you will see others with weird issues caused by the TPS. To really test it you need a graphing scanner--hook up scanner and open ubber slow--if it is starting to go bad--you will see a little anomoly in the graph--a curve with a small little difference......

 

you can use a multi meter and do a similar thing just look for a smooth incline and decline,
if there are any flat spots or sudden spikes this will or should be visible that way too.
Granted the graphing multimeter is better but not cheap!!!

 

by the way, plan on getting a new radiator or install an external tranny cooler if you haz an automatic. if you are doing all that work , do the radiator too trust bigballs here.

I have perfect maintenance record and my rad still let go and strawberried my tranny.
this was at 190,000

 

I do agree that the ridiculously over-priced Toyota coolant is better and lasts longer, but keep in mind, it didn't even come out till '99. I guess it wasn't too big of an issue since my '97 came from the factory with green coolant and my manual also says "use any ethylene-glycol based antifreeze". I have 198K on mine and no signs of any corrosion or other problems from using green coolant. My old water pump w/ 100K on it was also still in pretty good shape when I replaced it as maintenance a couple months ago.

 

I had a new aftermarket radiator installed at around 50K (I had a little front-end damage). I am hoping I am still in good shape as I effectively have only 90K miles on a non-Toyota radiator and have been using SLL coolant.
Knock on wood, I should be ok for a while.