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Oxygen Sensor Replacement
 
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Pelican Technical Article:

Oxygen Sensor Replacement

Jared Fenton

Time:

6 hours6 hrs

Tab:

$150 to $600

Tools:

Jack and jackstands, modified 22mm wrenches, patience

Applicable Models:

Porsche 955 Cayenne S (2003-08)

Parts Required:

New oxygen sensors.

Hot Tip:

Use a mirror to help you see the O2 sensors.

Performance Gain:

Better running engine.

Complementary Modification:

Replace fuel filter.

Replacing the oxygen sensors on the Cayenne is one of those jobs that will frustrate you. The oxygen sensors are located in an area where one is just barely visible, and the other requires you to use a mirror to see it. I'd suggest not planning anything else for the day if changing the sensors yourself. Owners of Cayenne Turbo models will have to remove the catalytic converters in order to access the sensors. On the Cayenne S, the sensors can be removed with the catalytic converter in place, but it is difficult. To replace the sensors at a dealer will cost well over $1000, so the frustration of doing this job may be worth it in the long run.

Porsche specifies the use of a Hazet torque wrench with removable wrench heads 4681-1, 4681-2 and 4861-3 to remove the sensors, although you can do the job with a few regular 22mm wrenches . You'll have to bend the open head of each wrench to allow enough offset to grip the sensor. This can be done by mounting a wrench in a shop vise and heating the wrench with a MAPP gas torch until its cherry-red. You can then use another wrench to bend the 22mm as needed. Obviously, use caution while doing this.

When you install the new sensors, thread them in by hand and torque them between 40-50 Nm (30-37 ft./lbs.). This can be difficult to do in the space allotted without the factory tool, but you can get them close enough by hand.

The oxygen sensors are a very important part of the fuel injection system. They measure the oxygen content of the exhaust and send signals to the fuel injection computer which in turn, will adjust the fuel/air mixture. When the sensors start to fail, you'll notice a loss of power, fuel economy and possibly a rich mixture smell coming from the tail pipe. This is because the engine goes into a default rich mode when it detects the oxygen sensor performance is below the regular limit. This will usually trigger a Check Engine Light (CEL) indicating that the sensor is failing. You can monitor the sensor function using the factory PIWIS computer or an aftermarket software package such as Durametric.

Many times, the CEL will note only one particular sensor that has gone bad. You can replace only that sensor although I usually recommend replacing all of the sensors at the same time, especially if the vehicle has 80-100,000 miles on it. It has been my experience that replacing only one leads to the others failing in a short amount of time.

To gain access to the sensors, you'll need to jack up the front of your Cayenne and place it on jack stands. Additionally, you'll need to remove the front under body trays. See our articles on Jacking Up Your Cayenne and Removing Under Body Trays for more information. Also note that for purposes of clarity, left or right sides of the car are viewed looking at the engine compartment from the driver seat.

Right side of car - These are the oxygen sensor electrical connections on the left side of the engine compartment on the firewall (green arrows).
Figure 1

Right side of car - These are the oxygen sensor electrical connections on the left side of the engine compartment on the firewall (green arrows). You need to disconnect the sensors before removing them to prevent the wire harness from twisting.

Left side of car - These are the oxygen sensor electrical connections on the right side of the engine (green arrow).
Figure 2

Left side of car - These are the oxygen sensor electrical connections on the right side of the engine (green arrow).

Both sides of car: Carefully wiggle each electrical connector out of the mounting bracket to access the locking tab (green arrow).
Figure 3

Both sides of car: Carefully wiggle each electrical connector out of the mounting bracket to access the locking tab (green arrow). Don't worry about mixing them up when attaching the new sensors. They are different shapes to prevent this.

Right side of car - To access the sensors on the left side of the car, jack up the front of your Cayenne, place it on jack stands and remove both wheels.
Figure 4

Right side of car - To access the sensors on the left side of the car, jack up the front of your Cayenne, place it on jack stands and remove both wheels. You'll want to crawl underneath the car directly behind the front strut. Look for the catalytic converter shown here (green arrow). The oxygen sensors on both sides are mounted both upstream and downstream of the converter.

Right side of car: If you look directly behind the catalytic converter, you'll see the post-catalyst oxygen sensor just above (green arrow).
Figure 5

Right side of car: If you look directly behind the catalytic converter, you'll see the post-catalyst oxygen sensor just above (green arrow). You'll need to use a 22mm offset wrench to remove the sensor. Carefully pull the sensor and wiring out from the car.

Right side of car: And here's the real chore in this job, removing the pre-catalytic converter oxygen sensor from the left side.
Figure 6

Right side of car: And here's the real chore in this job, removing the pre-catalytic converter oxygen sensor from the left side. You wont be able to see them very easily. They are located in the collector of the exhaust manifold (green arrow) facing the engine. You may need to place a mirror in the location of the yellow arrow to see it.

Left side of car: Shown here is the catalytic converter and exhaust (green arrows) on the right side of the car.
Figure 7

Left side of car: Shown here is the catalytic converter and exhaust (green arrows) on the right side of the car. This area is accessed by crawling under the front of the car right behind the front drive axle housing. The oxygen sensors are located in the general area of the yellow arrows.

Left side of car: In thisPicture, you can see the pre-catalyst oxygen sensor (green arrow) mounted in the bottom of the exhaust manifold collector, pointed towards the engine block.
Figure 8

Left side of car: In this picture, you can see the pre-catalyst oxygen sensor (green arrow) mounted in the bottom of the exhaust manifold collector, pointed towards the engine block. As you can see, access isn't the greatest.

Left side of car: In thisPicture you can just see the post-catalytic oxygen sensor mounted in the exhaust through the gap of the front sub frame and the chassis.
Figure 9

Left side of car: In this picture you can just see the post-catalytic oxygen sensor mounted in the exhaust through the gap of the front sub frame and the chassis. Use the offset 22mm wrench to reach and remove the sensor from the exhaust. Use a long screwdriver to open the clamp (yellow arrow) holding the wiring in place

The new oxygen sensors will come with a protective cap over the end of the sensor.
Figure 10

The new oxygen sensors will come with a protective cap over the end of the sensor. Carefully pull the cap off. Underneath, you'll see some anti-seize compound (green arrow) on the threads of the new sensor. Take care not to get any of this into the openings on the sensor (yellow arrow). This can damage the sensor. The hardest part of the whole job is manually screwing the sensors into the exhaust. It can be done with some patience.

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Comments and Suggestions:
Zachariah Comments: My 2006 Cayenne Turbo first displayed a P0431 code. I reset it and added a fuel system cleanerCRC GTP additive. It remained OFF for the entire remainder of the tankload. Just before I went to refill, a new code P0421 appeared twice. Exctly where is the Bank 1 pre-cat 02 Sensor?
November 28, 2016
  Followup from the Pelican Staff: right side of engine, sensor before catalyst. - Nick at Pelican Parts  
Greg Comments: I have an 2006 porsche cayenne S, I honestly can't tell how many Pre-cat sensors I have... 2? a Left? a right? are they both wide band 5-wire
May 10, 2016
  Followup from the Pelican Staff: Two pre-cat. 99% sure they are wide band.- Nick at Pelican Parts  
Gazza Comments: Dear Sir,

My model 957 showed codes P0391 and P0393. System too lean at idle bank 1 and bank 2. I have done nothing but only change the BMC air filter. May that cause the problem or something else? I appreciate your advise.

Regards,

Gary Lee
September 14, 2015
  Followup from the Pelican Staff: Maybe the duct is loose. Check if all the ducts are sealed and the air cleaner is properly installed. - Nick at Pelican Parts  

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