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Discussion Starter #1
My engine light was going on and off periodically, then finally stayed on. I had the muffler replaced this past weekend because of a hole in the top. While it was at the shop, the technician pulled a P0420 code and reset it. Two days later the light came back on so I took my truck to AutoZone to have the code pulled. Again, it was a P0420:

Catalyst system efficiency below threshold - Bank 1
Probable Cause:
1. Air leak in exhaust before rear HO2S
2. AF sensor error
3. Fule system fault
4. Faulty catalytic converter

Before I take my vehicle to Toyota and pay their ridiculously high "diagnostic fee", I'd like to get some opinions from the folks here. Am I seriously looking at replacing my cats? My truck is 7.5 years old with 52k miles.

Thanks in advance for your help.
 

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My engine light was going on and off periodically, then finally stayed on. I had the muffler replaced this past weekend because of a hole in the top. While it was at the shop, the technician pulled a P0420 code and reset it. Two days later the light came back on so I took my truck to AutoZone to have the code pulled. Again, it was a P0420:

Catalyst system efficiency below threshold - Bank 1
Probable Cause:
1. Air leak in exhaust before rear HO2S
2. AF sensor error
3. Fule system fault
4. Faulty catalytic converter

Before I take my vehicle to Toyota and pay their ridiculously high "diagnostic fee", I'd like to get some opinions from the folks here. Am I seriously looking at replacing my cats? My truck is 7.5 years old with 52k miles.

Thanks in advance for your help.
In all likelihood your O2 sensors are at fault. They are the cheapest and easiest to replace. Make sure you use Denso and NOT BOSCH. Here is a write-up:

http://www.tundrasolutions.com/forums/1197269-post2/

http://www.tundrasolutions.com/forums/engine-and-drivetrain/147864-tundra-o2-sensor-1-replacement/#post1127012
 

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Discussion Starter #3
From reading the two threads you posted links to, I see that "bank 1" is the driver side. Should I replace the front or rear sensor? Or both?

Thanks for your quick reply!
 

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Discussion Starter #5
The engine light was on prior to replacing the muffler. The technician at the muffler place pulled the code for me and reset the computer. Two days later the light came back on. AutoZone pulled the code for me and it was the same one---P0420.
 

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The code is for the rear O2 sensor since it is measuring the cat efficiency. I would do the sensor first, relatively cheap and easy to replace. The code is for a lean post cat condition so the other causes would be an air leak in the exhaust after the cat causing a false lean reading, or a lean fuel condition on that bank which should trigger a front O2 fault as well and you should notice running issues for that one. The last cause would be a cat not firing properly, hence the efficiency. For the record, my cats have 10 years and over 250,000 miles on them and are working fine.

If you had an OBDII scanner ( not just a code reader ) you could look at the short and long term fuel trims. The short term trims are primarily affected by the front (pre) O2 sensors, and the long term trims are affected by the post cat O2 readings. Proper short term readings will tell you that you are getting the proper amount of fuel on that bank, and if the post cat readings are lean ( poor effciency ) then it is either the post cat O2, an air leak ( you should hear a puffing noise ), or the cat. There are more diagnostics that can be done but this would be the place to start. Again do the sensor first then worry about the rest if that doesn't work.
 

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Discussion Starter #8
I figured an update was in order after replacing the sensor.

After soaking the bolts with PB Blaster I had trouble getting a wrench on the nuts. Then I realized that there weren't any... Apparently they had completely dissolved into rust. The gasket was disintegrated and the sensor and heat shield were stuck to the bolts by the rust, but came off easily.

Unplugging the sensor is easy, just get a small screwdriver. There is plenty of room to reach up there.

Since I had to buy new nuts, I found a reference to the P/N 90179-08059. A bit more research showed that it's a flanged M8 nut with a 1.25 mm thread pitch. A local shop sells only metric parts and tools, so I bought two stainless steel nuts for the princely sum of $0.45/ea. Toyota wants $2+ per nut.

You will definitely want to buy a thread chaser to clean the studs. Put a drop of light machine oil on the stud and run the chaser all the way down and back up again. Then clean the studs off to get rid of the grit.

I would recommend using a deep socket to screw the nuts down. The extra height will let you swing the wrench around a little further so the job goes quicker. The top one is a real pain because of the heat shield right above it.

Thanks everyone for the pointers! Rock Auto was very good. I ordered the sensor on a Friday and received it on a Monday, for $70 including shipping. Sweet!!
 

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I figured an update was in order after replacing the sensor.

After soaking the bolts with PB Blaster I had trouble getting a wrench on the nuts. Then I realized that there weren't any... Apparently they had completely dissolved into rust. The gasket was disintegrated and the sensor and heat shield were stuck to the bolts by the rust, but came off easily.

Unplugging the sensor is easy, just get a small screwdriver. There is plenty of room to reach up there.

Since I had to buy new nuts, I found a reference to the P/N 90179-08059. A bit more research showed that it's a flanged M8 nut with a 1.25 mm thread pitch. A local shop sells only metric parts and tools, so I bought two stainless steel nuts for the princely sum of $0.45/ea. Toyota wants $2+ per nut.

You will definitely want to buy a thread chaser to clean the studs. Put a drop of light machine oil on the stud and run the chaser all the way down and back up again. Then clean the studs off to get rid of the grit.

I would recommend using a deep socket to screw the nuts down. The extra height will let you swing the wrench around a little further so the job goes quicker. The top one is a real pain because of the heat shield right above it.

Thanks everyone for the pointers! Rock Auto was very good. I ordered the sensor on a Friday and received it on a Monday, for $70 including shipping. Sweet!!
More importantly, did the code disappear?
 

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Discussion Starter #10
DOH! I probably should have mentioned that...

Yes, the code disappeared. The engine light has not come back on during more than 700 miles of driving since replacing the sensor.

More importantly, did the code disappear?
 

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Similar situation for me.
2003 Tundra 4x4 V8 SR5...with 233,000 miles. Basically have been changing oil and tires, brakes. No major issues.
Truck began running "odd"...I could hear the engine sounding weak, like a spark-not or whatever it's called, as I began to accelerate, but then it would stop - or I could no longer hear it anyway. Put SeaFoam in it, a little better, but still kinda sluggish. Then, the CEL came on. Trusted repair shop who changed one of the O2 sensors. A week later, CEL came on again. Now, the 2nd O2 sensor gets changed. A couple days later, CEL again. This time they say the cat needs changing. After market replacement is made, just the converter. ON THE WAY home from the shop, CEL comes on again. I drove it over the weekend, feels fine, but I know the light is an indication (probably) of something wrong. Take it to Autozone, they check for code and it is P0420.
BTW, all work is done on Bank 1.
Any direction or thoughts would be appreciated.
 

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Similar situation for me.
2003 Tundra 4x4 V8 SR5...with 233,000 miles. Basically have been changing oil and tires, brakes. No major issues.
Truck began running "odd"...I could hear the engine sounding weak, like a spark-not or whatever it's called, as I began to accelerate, but then it would stop - or I could no longer hear it anyway. Put SeaFoam in it, a little better, but still kinda sluggish. Then, the CEL came on. Trusted repair shop who changed one of the O2 sensors. A week later, CEL came on again. Now, the 2nd O2 sensor gets changed. A couple days later, CEL again. This time they say the cat needs changing. After market replacement is made, just the converter. ON THE WAY home from the shop, CEL comes on again. I drove it over the weekend, feels fine, but I know the light is an indication (probably) of something wrong. Take it to Autozone, they check for code and it is P0420.
BTW, all work is done on Bank 1.
Any direction or thoughts would be appreciated.
What brand of 02 sensors?

What brand aftermarket convertor?
 

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I have this code and I'm going to do the sensor myself but I'm getting conflicting information. The guy at O'reilly told me I need the Denso O2 sensor PN# 234-4161. I went to order it on Amazon and they say this part does not fit my truck. Can anyone tell me what the PN was that you used?
 

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Discussion Starter #15
You might have better luck ordering from RockAuto.com. The Denso part numbers are:

Upstream Right & Left: 2344169
Downstream Right: 2344162
Downstream Left: 2344161
 

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You might have better luck ordering from RockAuto.com. The Denso part numbers are:

Upstream Right & Left: 2344169
Downstream Right: 2344162
Downstream Left: 2344161
Thanks.

They were actually cheaper than Amazon. I just bought all four for $183. I was at O'rielly yesterday and they wanted $99 for just the one and they were going to have to order it in. Glad I decided to order it myself.
 

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Discussion Starter #17
I've ordered nearly every replacement part from Rock Auto over the years. My wife has an '04 Highlander and I have an '03 Tundra. All the "wear parts" have come from Rock: O2 sensors, brakes, calipers, and even a gas cap. Their prices generally can't be beat and you'll receive your order in the mail within a few days.
 

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Does anyone have any tricks for rusted nuts? I got the downstream drivers side done, one nut came off fine and the other one was already gone. Moved over to the passenger side and the nuts are too rusted to get a socket or a wrench on. I tried some needle nose vice grips also but no luck there either. Anyone got a trick to share?
 

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Discussion Starter #19
Penetrating oil can help. I believe PB Blaster is the favorite around here. Also a small blowtorch like plumbers use can cause expansion in the metal, breaking the rust.
 

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Thanks for the response Paul. I did the PB Blaster but it didn't help. I borrowed a kit like this from my neighbor,



Turned them right off.


Also, for anyone else having any issues, another trick I picked up. I did all four sensors and for the life of me could not get the connections
clipped back together on the upstream passenger side. I could only get one hand up there then couldn't see what I was doing. I messed with it for at least 30 minutes before I gave up. Solution- Sweet talked my lovely bride and her little girly hands to climb down under my truck! We got down there (I held the light) She reached up with both hands with room to spare and see and CLICK! She even threw in a little smart ass comment like "Really...that little thing was kicking your ass!"
 
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