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Replacing Your Porsche 911 Carrera Oxygen Sensors
 
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Pelican Technical Article:

Replacing Your Porsche 911 Carrera Oxygen Sensors

Time:

1 hour1 hr

Tab:

$100 to $400

Talent:

**

Tools:

Floor jack and jack stands, 22mm wrench

Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 997 Carrera models (2005-08)

Parts Required:

New oxygen sensor

Hot Tip:

Use anti-seize compound on the threads of the sensor to make it easier to replace it next time

Performance Gain:

More accurate air/fuel mixture and better-running

Complementary Modification:

Install an aftermarket exhaust system or replace old exhaust gaskets

The oxygen sensor (also called an O2 sensor) is 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 level (14.6:1 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 a total of four on the Carrera--two for each catalytic converter on the car. The sensor located just in front of the catalytic converter measures the mixture of the exhaust gasses 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 light 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. If the signal received by the computer is out of its normal range, the 911 Carrera's computer will almost always give a warning signal that lights up the check engine lamp. Sometimes the computer may output an error code stating that the oxygen sensor is reading out of range, when in reality the values are out of range 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. For more info on reading these fuel injection codes, see Pelican Technical Article: Reading Porsche 911 Carrera Fuel Injection Fault Codes.

If you disconnect the oxygen sensor and ground it to the chassis, the ECU will think that the car is running lean (not enough fuel), and will try to richen the mixture. At the other extreme, if you disconnect the oxygen sensor, and replace it with a small AA battery that supplies 1.5 volts, the ECU will think that the car is running really rich and attempt to adjust the mixture to be leaner.

Needless to say, 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 every 30,000 miles. You have to jack up the car to gain access to the sensor (see Pelican Technical Article: Jacking Up Your Porsche 911 Carrera).

Using a 22mm wrench, simply remove the sensor from the exhaust pipe. On the Carrera, the sensors are very easy to reach. On many other cars, you would need a special deep socket with a slit cut in the side to remove it. The electrical plug for the O2 sensor simply unplugs from the chassis plug. New O2 sensors should have the same exact plug--ready to attach to your car. When you remove the O2 sensor, you will probably find that it is coated with black soot. This is normal for an old, worn-out O2 sensor. On our project car here, the O2 sensor was covered in motor oil and coolant. This is a bad sign that corresponded with the seized engine in my project car (I bought it that way). See Project 13 for more details on the problems sometimes found with these late-model Porsche engines.

Install your new sensor snug-tight, or if you have the proper slit-tool and a handy torque wrench, then tighten it to 40 ft-lbs (55 N-m). It's also a smart idea to add some anti-seize compound to the threads of the plug before you install it, but make sure the anti-seize doesn't get into any of the slits on the head of the sensor. Check the sensor first though, as new ones sometimes come with anti-seize already on the threads.

There are two different types of sensors you can purchase--generic ones that allow you to snip the connector off of the old sensor and put it on the new one, and original OEM sensors with the correct connector. On older cars, I used to use the generic sensors, but I've had problems with using them on these newer cars. Researching further, I discovered that the wires and connectors are very important on these O2 sensors. The Porsche factory workshop manuals state the following:

"911 Carrera 4 has a new, water-proof oxygen sensor. Water-proof means that the upper sensor section and housing are connected leak-proof with a later welded seam and previous reference air openings are omitted. Reference air is now taken via the connecting lead and plug connection. For this reason it is important to keep contact solutions, lubricants, liquids or similar products out of the 3-pin plug, since they would lead to sensor failure"

Soldering wires together can interrupt the reference air signal and lead to problems with the sensor. I've also had problems with the Bosch factory Posi-Lock connectors that are supposed to work with these newer sensors. Because the relationship between the connector and the O2 sensor is so vital to the proper reference signal, I recommend that you only use the correct sensors with the proper plug.

Shown here are the two Oxygen sensors for the passengers side of the car (red arrow shows the pre-catalytic, yellow shows the post catalytic converter).
Figure 1

Shown here are the two Oxygen sensors for the passengers side of the car (red arrow shows the pre-catalytic, yellow shows the post catalytic converter). On the 997 Carreras one of the sensors is located on the catalytic converter, but the removal and replacement procedure is the same. The green arrows, show the wires that go to the engine shelf, where the connectors are located. I have often found that the new O2 sensors come with the correct plug, but sometimes the cable is way too long. If this is the case, then secure the cable with a nylon zip tie. Make sure that the cable is not located anywhere near any exhaust components--you don't want the heat melting the cable to the O2 sensor. The photo inset shows the special tool that is sometimes required to remove O2 sensors in hard-to-reach places (available from PelicanParts.com).

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Comments and Suggestions:
HectorVon Comments: Hello, I have a 99 Carrera and check engine light came on and when i ran a test i got an error code saying Bank1 Cyl 1-3 and also Bank2 Cyl 4-6 so i went and changed all four sensors with Bosch sensors but after 50 miles the Check engine has came up again, what can it be now?
October 31, 2016
  Followup from the Pelican Staff: What fault code(s) are stored? - Nick at Pelican Parts  
gary_cs Comments: I have a 2000 Carrera Cab my OBD code is P1126 02S Sensing Range 1 CYL 4-6. I bought a new Oxygen Sensor is CYL 4-6 the passengers side?
July 17, 2016
  Followup from the Pelican Staff: Yes, passenger side. - Nick at Pelican Parts  
Mike c2 Comments: I have a 2000 c2 w/ tpc supercharger, after I replaced one of the oxygen sensor it's been throwing p1128/p1130. I need to clear it as I can't get the car to go get it's drive cycle. Thanks as always
June 12, 2016
  Followup from the Pelican Staff: You may have the wrong part installed. Have you confirmed the signal is present at the DME? - Nick at Pelican Parts  
marccon Comments: Have an issue with a lumpy tick over. no errors showing, however using torque app with ELM 327 interface I get the following readings. Not very sure what sensor/s they identify but apparently identifying the cause of the tick over problem I think?

Can any of you guy's help?????????
Old Today, 12:29 PM
May 16, 2016
  Followup from the Pelican Staff: You are looking at Mode 6 data, only helpful if you have an intermittent fault code. The test results show an issue with an o2 sensor. You will need the mode 6 sheet for your vehicle to determine which sensor it is.

I would check the engine for vacuum leaks, to see if it is affecting the slow response time.- Nick at Pelican Parts
 
Frankie Comments: Hello, I have code P0420 Catalyst System Efficiency Below Threshold Bank 1. Should I replace the sensors first to see if that fixes the problem or is it telling me that I need a catalyst converter?
Thanks!
April 22, 2016
  Followup from the Pelican Staff: No, the o2 have to pass a monitor before the cat monitor runs. Your cat is likely faulty. - Nick at Pelican Parts  
mr.cal Comments: So I just installed aftermarket cats on my 2000 996. The pre- cat sensor hole is in the same place as stock, the after cat hole is way at the end of the pipe and that cable is way too short. Does it matter if I use the post cat sensor from the other side , as it drops right on top of the hole from the other cat? Hope this makes sense. Thanks !
December 18, 2015
  Followup from the Pelican Staff: The sensor have to be for the side they are wired for, or fuel control faults will set. You will have to relocate the o2 sensor bung. - Nick at Pelican Parts  
Ron Comments: I have a 2001 996 convertable and I have to change out an 02 sensor at bank 1 sensor 2.
where is this located on the car? is it easy to change out? Also, I have to replace the coolant temperature sensor. Where would this be located on the car? I ordered the parts from you today.thanks! Ron
November 20, 2015
  Followup from the Pelican Staff: Left side of vehicle, when sitting in it. The sensor is located in the exhaust, you will access it from below. Look for the sensor after the cat.- Nick at Pelican Parts  
onekrishnakumar Comments: Hello

I have a 2005 911 Cab Manual. When I scanned it with my Durametric scanner, I got a code # P0036. The following is the description of the code "Final Stage for Heater of Oxygen Sensor behind cat. conv. bank 1".

To me this sounds like the heater of the oxygen sensor is not working or is in its final stages. So is the heater for the oxygen sensor built into the oxygen sensor ? In other words would this code be cleared if I replace the oxygen sensor or is there a separate oxygen sensor heater that I should replace ?

Thanks
October 14, 2015
  Followup from the Pelican Staff: This code is for the heater. I would replace the sensor. - Nick at Pelican Parts  
gewdraa Comments: Hi, could you check the arrow information, surely the flange with three bolts in the picture is the pre cat sensor. yellow arrow and the red is the post cat sensor leading to the exhaust muffler, kind regards, chris
May 27, 2014
  Followup from the Pelican Staff: I will have someone look into it. Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
MasterG Comments: Gentlemen,
Great articles as always!
I have a 1999 Carrera 4 /3.4/M96.At 100k...Completly rebuilt engine.Might just need oxygen sensors replaced at this time.For my time,money and effort....If 1 is bad i change them all.

In reference to your article you say "The correct sensor"..
Bosch has always served well in most applications.
What is the best and most superior 02 sensor for this application.Shortly..will be needing the set of 4

Thanks as always!
December 4, 2013
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need. - Nick at Pelican Parts  

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