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.

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

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!

Were you getting the code prior to the exhaust work?

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.

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.

Doesn't federal law require them to warranty this stuff for like 7 years and 80,000 miles or somethng.

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!!

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?

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?