Pelican Parts
Volkswagen Parts Catalog Accessories Catalog Volkswagen How To Articles Volkswagen Tech Forums
Call Pelican Parts at 888-280-7799
View Recent Cars  |Shopping Cart Cart | Project List | Order Status | Help
Bookmark and Share

Pelican Technical Article:

Oxygen Sensor Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$150 to $400

Talent:

**

Tools:

22mm, 10mm wrench, 22mm crows-foot wrench, jackstands

Applicable Models:

VW Golf GTI (2000)
VW Golf GTI 1.8T (2002-05)
VW Golf GTI 20th Anniversary (2003)
VW Golf GTI 337 (2002)
VW Golf GTI GLS (2001)

Parts Required:

New O2 sensors

Hot Tip:

Do not get anti seize on the sensor

Performance Gain:

Car runs better.

Complementary Modification:

Oil Change

The oxygen sensors (also called O2 sensors) are one of the most important elements of the modern fuel injection systems. A finely tuned fuel injection system with an oxygen sensor can maintain an air/fuel ratio within a close tolerance of .02 percent. Keeping the engine at the stoichiometric ratio (14.7:1 air/fuel ratio) helps the engine generate the most power with the least amount of emissions.

The oxygen sensors are located in the exhaust system of the engine, and they sense the oxygen content of the exhaust gases. There are two on the GTI MkIV: one on each side of the catalytic converter. The sensor located just in front of the catalytic converter measures the mixture of the exhaust gas exiting the engine. The sensor located after the catalytic converter is used to measure the performance of the converter by comparing the O2 levels before and after. The amount of oxygen in the exhaust varies according to the air/fuel ratio of the fuel injection system. The oxygen sensor produces a small voltage signal that is interpreted by the electronic control unit (ECU) of the fuel injection system. The ECU makes constant adjustments in fuel delivery according to the signal generated by the oxygen sensor in order to maintain the optimum air/fuel ratio.

There are a few signs that your oxygen sensor may be failing. In general, it is difficult to diagnose problems with the sensor, unless all of the other components in the fuel injection system have been checked and determined to be operating correctly. Some of the symptoms of a failed oxygen sensor system are: Irregular idle during warm-up, irregular idle with warm engine, engine will not accelerate and backfires, poor engine performance, fuel consumption is high, driving performance is weak, CO concentration at idle is too high or too low, check Engine Lamp is illuminated.

In general, if the oxygen sensor is not working, the car will be running very poorly, and will also be outputting a lot of harmful emissions. The cars computer will usually give a warning signal that lights up the Check Engine Lamp if the signal received by the computer is out of its normal range. Sometimes the computer may output an error code stating that the oxygen sensor is reading out of range, when in reality the values registered by the O2 sensor are accurate because there is something else wrong with the fuel injection system. Prior to replacing the oxygen sensors, make sure there are no other codes being recorded that may affect the O2 sensor readings.

Always purchase the correct sensor for the car. The wire resistance and proper connection to the harness are vital for the performance of the sensor. Snipping and soldering wires together can affect the resistance in the wire and cause the sensor to give false readings. While the factory sensors are expensive, in the long run you will probably not end up saving yourself any money and end up doing the same job twice if you install cheap generic sensors.

Troubleshooting the complete fuel injection system is beyond this project's scope. If you think that the oxygen sensors may be causing some of your fuel injection problems, they should be replaced. In general, I recommend that you do this as needed. You will have to jack up the car and secure it safely on jackstands to gain access to the sensors. Please see our article on safely jacking up and supporting your vehicle.

ALWAYS work on a cool car and exhaust system.

There are two oxygen sensors on the GTI MkIV.
Figure 1

There are two oxygen sensors on the GTI MkIV. One pre catalytic converter (yellow arrow) and one post catalytic converter (red arrow). The housing that protects the electrical connections in located just under the car below the right side seat (green arrow).

Begin by removing the two 10mm plastic nuts that hold the housing in place (red arrows).
Figure 2

Begin by removing the two 10mm plastic nuts that hold the housing in place (red arrows).

Pull the housing down and turn it over.
Figure 3

Pull the housing down and turn it over. Inside are the two connections for the pre (green arrow) and post (red arrow) catalytic O2 sensors. The connections are different sizes and types and can only sit in the housing one way.

Unclip the two different connections for the pre (green arrow) and post (red arrow) O2 sensors.
Figure 4

Unclip the two different connections for the pre (green arrow) and post (red arrow) O2 sensors.

Follow the wires back to the sensors unclipping them from the harness clips (red arrows) as you go.
Figure 5

Follow the wires back to the sensors unclipping them from the harness clips (red arrows) as you go.

There is a small piece of heat shield material (red arrow) on the wires towards the front of the cat.
Figure 6

There is a small piece of heat shield material (red arrow) on the wires towards the front of the cat. Unclip this and set it aside.

On some systems it is a lot easier to remove the sensors with the special 22mm crows foot O2 sensor removal tool (red arrow).
Figure 7

On some systems it is a lot easier to remove the sensors with the special 22mm crows foot O2 sensor removal tool (red arrow).

Figure 8

The forward sensor is easy to remove with a regular 22mm wrench (red arrow)

This photo illustrates the old O2 sensor.
Figure 9

This photo illustrates the old O2 sensor. It is almost impossible to tell if the sensor is functioning correctly just by looking at it (red arrow). When installing your new sensor apply a little high temperature anti-seize to the threads (yellow arrow) taking extreme care not to get the anti-seize on the end of the sensor. Check your new sensor first, lots of new ones come with the anti-seize installed already. Installation is the reverse of removal. Use care when screwing in the new sensor that you do not cross thread it. The procedure is the same for both O2 sensors.

Bookmark and Share
Comments and Suggestions:
sirrolex Comments: how many/location of O2 sensors in AGN 1.8 engine in golf MK4
November 16, 2016
  Followup from the Pelican Staff: What year and model? - Nick at Pelican Parts  
Pet Comments: What are the symptoms of bad oxygen sensor? I have VW MK4 1.6 AEH, and my fuel consumption is horrible. It's around 11l/100km. When I scan the ECU the only code that pops up is the LAMBDA OXYGEN SENSOR: 00537 - Lambda Oxygen Sensor Regulation: Lower Limit. Will replacing the oxygen sensor fix the bad fuel consumption? Thanks
September 28, 2016
  Followup from the Pelican Staff: Usually nothing. Bad o2s usually set fault codes.

You could have a fuel trim issue. If fuel trim is not skewed the sensor may be faulty. - Nick at Pelican Parts
 
arel Comments: After instaling, a calibration is needed with a diagnosis or not ?
August 6, 2016
  Followup from the Pelican Staff: No, just clear fault codes if any were stored. - Nick at Pelican Parts  
sue Comments: Could a 02 sensor have been damaged when fitting a new fuel filter?
February 16, 2015
  Followup from the Pelican Staff: I don't see how. Unless it was physically damaged from impact. - Nick at Pelican Parts  

QUICK LINKS
About Us
Careers
Pelican Parts, Inc.
1600 240th Street
Harbor City, CA 90710
Order Online or Call:
888-280-7799
CONNECT WITH US
NEWSLETTER
Sign Up for Pelican Pit Stop News & Special Offers
Page last updated: Thu 2/23/2017 02:39:01 AM