Can a P0138 code be caused by a bad upstream O2 sensor?

[TheTank67]

So I got the dreaded P0138 this week. I swapped out the downstream sensor and drove 10 miles to Home Depot. Got back in the Jeep and drove her back home and a couple minutes from home, the CEL came on again. It still says P0138. Any ideas? Can the upstream sensor cause this? It's a 2001 BTW.

 

[TheTank67]

Also, does the 2001 2.5L 4 banger just have the two sensors and not four?

 

[Willys LJ]

What brand sensor? TJs are a bit particular on that. They prefer Mopar or NTK. Other brands can cause "transplant rejection". I think it's in their DNA.

I believe the 4 cyls and early 6 cyl TJs just have 2. The later 4.0s have 4.

 

[Chris]

I'm guessing you didn't use NTK O2 sensors, right? If so, that's likely your issue.

See this thread: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Also, you need to replace ALL O2 sensors at the same time, not just the one that is bad. O2 sensors are a general wear and tear maintenance item, and should ALL be replaced every 80k miles or so if you want your vehicle to be running as good as possible.

 

[CharlesHS]

The code is caused by ECM not seeing a large enough difference in the oxygen content between the front and rear O2 sensors.
Years ago I saw a similar code when I installed a catalytic converter test pipe in an '06 RSX-S while operating KPro.
There are many things that can cause the P138 code...
A bad or poor quality O2 sensor is at the top of the list.
Next would be a poorly operating catalytic converter.

 

[TheTank67]

I'm guessing you didn't use NTK O2 sensors, right? If so, that's likely your issue.

See this thread: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Also, you need to replace ALL O2 sensors at the same time, not just the one that is bad. O2 sensors are a general wear and tear maintenance item, and should ALL be replaced every 80k miles or so if you want your vehicle to be running as good as possible.

Thanks for the reply. No. All they had at O'Reilly was Bosch parts.

I saw the links you provided on another thread but the sensors look quite a bit different from the original part. To be clear, the 2001 TJ Wrangler 2.5L 4Cy uses NTK 23141 for the downstream and NTK 23138 for the upstream? As I said they physically look different so just want to verify that is what I need to buy.

On another note, I bought this Jeep last year and the previous owner put oversize tires on it. I'm lucky to do 60MPH on the highway (if I draft behind another vehicle). What is going on there? Gear ratio?

Thanks for creating this site!! I just found it this weekend but will be checking back regularly. This is a project vehicle and I plan to keep it for the foreseeable future and I plan to keep upgrading it as I go along.

 

[Chris]

Thanks for the reply. No. All they had at O'Reilly was Bosch parts.

I saw the links you provided on another thread but the sensors look quite a bit different from the original part. To be clear, the 2001 TJ Wrangler 2.5L 4Cy uses NTK 23141 for the downstream and NTK 23138 for the upstream? As I said they physically look different so just want to verify that is what I need to buy.

On another note, I bought this Jeep last year and the previous owner put oversize tires on it. I'm lucky to do 60MPH on the highway (if I draft behind another vehicle). What is going on there? Gear ratio?

Thanks for creating this site!! I just found it this weekend but will be checking back regularly. This is a project vehicle and I plan to keep it for the foreseeable future and I plan to keep upgrading it as I go along.

Those Bosch sensors are going to give you issues, you can count on it.

As for the speed issue, the 2.5 4 cylinder is a very, very poor highway vehicle. With oversize tires and the stock 4.10 gears, it will barely maintain highway speeds.

The smart thing to do is re-gear, but even then, the 4 cylinder models are just not meant for long highway travel, as they have trouble maintaining highway speeds due to lack of power.

 

[TheTank67]

Those Bosch sensors are going to give you issues, you can count on it.

As for the speed issue, the 2.5 4 cylinder is a very, very poor highway vehicle. With oversize tires and the stock 4.10 gears, it will barely maintain highway speeds.

The smart thing to do is re-gear, but even then, the 4 cylinder models are just not meant for long highway travel, as they have trouble maintaining highway speeds due to lack of power.

Thanks for the quick reply. This is actually a vehicle I bought for my teenage daughter so I'm ok with it not going fast on the highway...except when I drive it. haha.

Were those part numbers correct? I want to get those ordered and installed asap because the inspection went out during all this COVID=19 BS and it didn't pass muster.

 

[Chris]

Thanks for the quick reply. This is actually a vehicle I bought for my teenage daughter so I'm ok with it not going fast on the highway...except when I drive it. haha.

Were those part numbers correct? I want to get those ordered and installed asap because the inspection went out during all this COVID=19 BS and it didn't pass muster.

Sounds like it may be a win-win then!

I pulled those part numbers directly from the NTK website. You can look them up just to double check, but that's where I pulled them from.