Rocky Mountain Club B5

Discussion Forums => Modifications => Topic started by: SweetVW on January 23, 2005, 08:12:03 PM

Title: Pre-cat O2 sensor install
Post by: SweetVW on January 23, 2005, 08:12:03 PM
First, I need to give Colin (CB5) kudos for the original write-up.  I will use his comments as needed.  I will update and add pics to assist for future use.

Please read this disclaimer ( before doing any work on your vehicle.

Vehicle used:
2000 1.8T tip

Time required ~45 minutes.

Tools needed:
1. Wire cutters/knife to cut old 02 sensor and zip tie.

2. High-temp. anti-seize (unless otherwise coated)

4. Torque wrench

5. Zip ties

5. Thin flat head screwdriver and phillips (if needed)

6. 7/8" wrench as I couldn't find the correct size in
    millimeters which I think is 20mm or 21mm. Craftsman 7/8"
    worked perfectly though.


1. First! and this is important, trace the sensor wire back to the plug before doing any cutting of the wire.  I initially thought that the sensor was plugged into the brown plug, I was wrong it was the black one.
2. Remove air filter box.
Those with xenon headlights, the ballast sits right in front of the air box, it was easier to move the headlight forward (without disconnecting it) to allow more room to work the air filter box out.  A 10mm wrench will work to loosen the bolt connecting the filter bottom to the frame.

3. Cut the wire by the sensor, leaving about 3-4" just to be able to remove the sensor with ease.  Side note: I pulled the wire from the plug side; it kept the remaining bigger VW specific zip ties intact.

4. Remove the sensor.  I found that with the air box completely removed, I could fit a 7/8 wrench without problem.  The sensor came out pretty easy with a little muscle, no problem, and no breaker bar necessary.

5. Attach new 02 sensor and torque to 37 ft lbs.  Make sure it either has anti-seize on it, or put some on yourself.  And make sure it's "high-temp." Don't allow anything to touch the sensor!

6. To remove the remaining cable going back to the plug, you only need to remove one zip tie, which is attached to a boss on the back of the cylinder head.
(This picture was taken after I installed the sensor, the stock zip is a 8 shaped double zip tie.)

Removal of the bigger VW specific ties holding the remaining wires in place is not necessary.

7. Remove the old 02 wire, tracing it to the firewall, and unplug the old sensor, using a flat head to work it loose ever so gingerly... you don't want to break the coupler, it comes off easy.  (I found that removing the coolant tank gave more room to work with.)
8. Take note to follow the path of the old wire and try to follow it with the new one.  I found that I had to zip tie along a few spots leading back to the plug.

9. That is about it!
Title: Pre-cat O2 sensor install
Post by: jayryan on January 24, 2005, 03:49:14 AM
Awesome write-up! Maybe I'll throw this in the 100K tune-up. Also, since Jay or Winston will probably post it up in the tech forums, you could just make a note to read the disclaimer thread before continuing. ;)
Title: Pre-cat O2 sensor install
Post by: SweetVW on January 24, 2005, 04:24:00 AM
Done.  Thanks for the comment.
Title: Pre-cat O2 sensor install
Post by: ColoradoB5 on January 24, 2005, 08:46:06 AM
Great writeup Dave.  Jay will post this into the Tech forum, I am sure.