CEL Codes 25 & 26 (1 Viewer)

[BTLSHP]

CEL 25 & 26 came on yesterday. The engine is running without any noticeable issues. I am getting 13.4mpg in mixed driving.

Is this a simple case of my not replacing both sensors in August? The inboard sensor was replaced in 2015, so under 25k miles ago. So, given the location I skipped it. The outboard sensor failed due to the heater circuit. I am aware these are sold in pairs.

Looking at the table on EG-224 under Diagnostics item 3 gives my pause - differences between air/fuel compensation vales from the two 02 sensors. Visually, I have seen differences on my little ToyoOBD device. I would have to find a way to download the data files to confirm they are outside 15%. It came on during urban 35-45mph driving.

 

[BTLSHP]

Ok, I have learned a lot but may still have some issues. The "NTK" I ordered on Amazon to replace the outboard (right) sensor failed late last fall. I ordered two 89465-69115 from Japan, the delivery time was protracted but they arrived last week.

I replaced the outboard sensor immediately, I have left the inboard in place largely because I have no clue how to remove it. That said it is a Toyota sensor that went in 29,000 miles ago in 2015.

When I button things up and drove it CEL 25/26 came back. Reading the manual and other threads I decided not to concentrate on the lower probability issues as the engine runs very well. I have some gas mileage concerns but realize we are on winter fuel now.

The resistance at the diagnostic port looked ok an both sensors seem to be actively cycling at 2,000rpm. But looking at the car side of the connectors I found greenish corrosion looking like below. I disconnected the battery cleaned the area with baking soda and water followed by an alcohol rinse. After drying time I put things back together and no CEL over a few era runs. The FSM has a test rive for these codes, but I would have to drive quite a distance to find an open road for this drive.

What is the probability that cleaning the corrosion is enough to clear this code?

 

[Rifleman]

The way your outboard sensor is mounted needs to be changed if your truck is a 93-94,

The reason i say that, the factory mounting position for the O2 sensor on the 93-94 trucks has the connector mounted in a vertical position,

What this allows is water to collect in that connector because the bottom half of that connector acts just like a cup,

What i did on my truck was to remount that connector so it's held in a horizontal position, preventing it from collecting and holding any water,

That change ended my corroded terminal problem, also eliminated my code 25-26 problem,

 

[BTLSHP]

The way your outboard sensor is mounted needs to be changed if your truck is a 93-94,

The reason i say that, the factory mounting position for the O2 sensor on the 93-94 trucks has the connector mounted in a vertical position,

What this allows is water to collect in that connector because the bottom half of that connector acts just like a cup,

What i did on my truck was to remount that connector so it's held in a horizontal position, preventing it from collecting and holding any water,

That change ended my corroded terminal problem, also eliminated my code 25-26 problem,

Ah! that is a fix I can make. Thanks for the tip!