Toyota Tundra Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
987 Posts
Discussion Starter #1
I did a search for this and didn't find any discussions on this, so I thought I would share. My check engine light came on a few weeks ago. 2007, 5.7l, 114,000 miles. A quick check with a scanner I purchased at Amazon showed a P0138 code, Bank 1, Sensor 2. I ordered the factory Denso sensor from Rock Auto and the other downstream sensor, Bank 2, Sensor 2. It is suggested to replace both downstream or both upstream sensors if one fails. These are the O2 sensors behind the catalytic converters. Easy to install (use the copper anti-seize). Reset the light and took it for a drive. About 30 minutes into the drive the light came back on. Another check with the scanner showed the same code.

I checked all the wiring, tested the wiring for voltage and made sure the new sensor was good. No issues there. Other causes could be faulty fuel injectors, bad Cat, etc. I noticed my exhaust smelled like rotten eggs. I took a leap and ordered the front two (upstream) air/fuel sensors that are ahead of the Cats even though the CEL didn't show a fault there. They are double the cost of the rear sensors. Swapped them out, reset the light and the problem is now fixed. My exhaust also smells normal now. Apparently a bad upstream sensor can cause a fault with a downstream sensor. The sensors have about a 100k life anyway, so replacing all four is probably a good idea anyway.

Total cost, including the four sensors and scanner, just over $400. Far cheaper than the dealer. I hope this helps anyone else with the same problem.
 

Attachments

·
Registered
Joined
·
830 Posts
The Downstream sensors are usually only replaced singles as needed because they are just there to check the cats are working within spec. I always replace the upstream A/F O2 sensors as a pair especially if the are in or over the 150k mile range. The A/F affects the engine fuel trim and "tune" and can be considered like tuning a carb (same as MAF sensor). The downstream performance codes can be caused by bad upstream sensors because the computer compares the downstream sensors to the upstream sensors. All of those sensors age and get buildup on them.
You will likely notice a mpg increase especially now if you clean the MAF and theottlbody. Reset the computer by disconnection the negative battery terminal for 2 min for a faster relearn and tune. You might be surprised by what that does for pepping it up.
 

·
Registered
Joined
·
987 Posts
Discussion Starter #3
The Downstream sensors are usually only replaced singles as needed because they are just there to check the cats are working within spec. I always replace the upstream A/F O2 sensors as a pair especially if the are in or over the 150k mile range. The A/F affects the engine fuel trim and "tune" and can be considered like tuning a carb (same as MAF sensor). The downstream performance codes can be caused by bad upstream sensors because the computer compares the downstream sensors to the upstream sensors. All of those sensors age and get buildup on them.
You will likely notice a mpg increase especially now if you clean the MAF and theottlbody. Reset the computer by disconnection the negative battery terminal for 2 min for a faster relearn and tune. You might be surprised by what that does for pepping it up.
I'll do that, thanks for the info!
 

·
Registered
Joined
·
6 Posts
I did a search for this and didn't find any discussions on this, so I thought I would share. My check engine light came on a few weeks ago. 2007, 5.7l, 114,000 miles. A quick check with a scanner I purchased at Amazon showed a P0138 code, Bank 1, Sensor 2. I ordered the factory Denso sensor from Rock Auto and the other downstream sensor, Bank 2, Sensor 2. It is suggested to replace both downstream or both upstream sensors if one fails. These are the O2 sensors behind the catalytic converters. Easy to install (use the copper anti-seize). Reset the light and took it for a drive. About 30 minutes into the drive the light came back on. Another check with the scanner showed the same code.

I checked all the wiring, tested the wiring for voltage and made sure the new sensor was good. No issues there. Other causes could be faulty fuel injectors, bad Cat, etc. I noticed my exhaust smelled like rotten eggs. I took a leap and ordered the front two (upstream) air/fuel sensors that are ahead of the Cats even though the CEL didn't show a fault there. They are double the cost of the rear sensors. Swapped them out, reset the light and the problem is now fixed. My exhaust also smells normal now. Apparently a bad upstream sensor can cause a fault with a downstream sensor. The sensors have about a 100k life anyway, so replacing all four is probably a good idea anyway.

Total cost, including the four sensors and scanner, just over $400. Far cheaper than the dealer. I hope this helps anyone else with the same problem.
How difficult to replace the front sensors?
Thanks!
 

·
Registered
Joined
·
830 Posts
Your question is relative to you, O2 sensors are easy but sometimes the upstreams can be a little harder to get to. You tube it!
Essentially, PB Blaster them, disconnect neg. battery terminal to reset computer while you work, disconnect sensors, remove with O2 sensor socket or tube wrench , new sensor with anti-sieze, wrench again, plug in sensors, reconnect battery, start, start again, let idle for 10 min before driving.
 

·
Registered
Joined
·
6 Posts
Guess I should have worded my question differently, lol.
How big of a pita are they to get too? Ive changed them before on other vehicles some are easy and some suck.
 

·
Registered
Joined
·
830 Posts
Guess I should have worded my question differently, lol.
How big of a pita are they to get too? Ive changed them before on other vehicles some are easy and some suck.
I have not done a set on the 5.7L before, I only had it for a couple years. For sure one of those things a lift would make easier though. Maybe someone else who has done them can chime in.
 
1 - 7 of 7 Posts
Top