O₂ Sensor replacement on 2.4L 2006 Sonata

I wrote this article to save you a few hours of research and some money.

If you happen to have a 2006 Hyundai Sonata, it seems that around 100.000 miles (160.930 km) you need to replace the oxygen sensors. If you don’t do so your catalytic converter will go bad; that is much more expensive.
This is not rocket science, however it requires some basic skills.

You need Oxygen sensor(s), 7/8 inch (22mm) oxygen sensor socket (with a groove in the middle for the cable) and ratchet for it (a long one since it can be hard unscrewing the old ones), anti-seize, gloves, and patience.

7/8-Inch – 22mm Oxygen Sensor Socket

I suggest go with Japanese parts.
Front: Denseo part number 234-4433, rear: Denseo part number 234-4439.

On the 4 cylinder, 2.4L engines you have two. One before the catalytic converter (front) and one after (rear). I don’t know how it is on the 6 cylinder ones.

The sensors are located somewhere under the windshield wipers. If you stand in front of the car looking at the car the front one is on the left side and the rear one on the right.






The front one has a ring on it and the sensor itself is a tiny bit thicker. Don’t mix them up!

Front / Upstream
Rear / Downstream

The sensor replacement has to be done with a cool engine; it is easier to unscrew the old one(s) and you also won’t burn yourself. Before you insert the new ones put anti-seize only on the screw part of them.

If you are here you should know already how to connect a OBDII scanner to your car and read values with your phone or dedicated tool. I use Panlong WiFi OBD2 tool and FourStroke app, which is free; however if you want to read O₂ levels then you’ll need the premium version ($3,99). Mostly you need to check your O₂ sensors voltage. This should jump between 0.1V and 0.9V, more about them here. If you see their value is moving between these two values then your job was done, all should be good.


Warning! Do the work at your own risk! If you are not sure what to do and lack basic car repair competence, don’t do it

PS: After changing the O₂ sensors and cleaning the Mass Airflow Sensor my gas consumption went down about 5%.


OS-X – change username/home directory – El Capitan

As you may know when you change your username in OS-X you must change the home directory as well to match the new username (https://support.apple.com/en-us/HT201548).

Now in El Capitan when you change the home directory you get an extra “/” at the end of the username and it is going to be in your $HOME environment variable as well: /Users/myusername/. This information is provided by launchd. It can be changed from .profile or .bash_profile but it won’t take effect everywhere in the system but in terminal.

This doesn’t look like a big issue at the first glance however it might be. Some applications refuse to run if there is a discrepancy between $HOME env variable and value returned by NSHomeDirectory().
I had issues running Tunnelblick. “The checks are performed to help prevent attacks like the Bourne-Again Shell (Bash) Remote Code Execution Vulnerability.”


Luckily there is an easy fix.

  1. Create a new directory under /Users/temporarily
  2. Create a new admin user if you don’t have one already
  3. Sing out from the user with issues and log in to the other user
  4. Go to System Preferences -> Users&Groups -> hit the lock icon -> right click on the troubled user name then Advanced Options
  5. Choose the directory you’ve created in step 1 (/Users/temporarily) -> click OK
  6. Click the lock again to lock it
  7. Right click again on the troubled user name and click Advanced Options -> Type in the correct home directory without the forward slash at the end /Users/username -> click OK
  8. Login with the user you had issues and you should be done, and you can remove /Users/temporarily directory

I want to thank for the help of the Tunnelblick debugging the app and Apple’s customer care who confirmed the bug and helped with the work around. Apple shall come up with a bug fix in their next release.