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Special Tool(s)
Socket, Exhaust Gas Oxygen Sensor 303-476 (T94P-9472-A)



Removal and Installation

1. Raise and support the vehicle.

2. Disconnect the heated oxygen sensor (HO2S) electrical connector.



3. NOTE: If necessary, lubricate the HO2S with Penetrating and Lock Lubricant E8AZ-19A501-B or equivalent to aid in removal.
* Using the special tool, remove the HO2S.



4. NOTE: Apply a light coat of High Temperature Nickel Anti-Seize Lubricant F6AZ-9L494-AA or equivalent meeting Ford specification ESE-M12A4-A to the threads of the HO2S to aid in installation.
* To install, reverse the removal procedure.
 

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I replaced these sensors successfully. My goal was to replace the "upstream" oxygen sensors before they went bad. My Escape has 149,000 miles on it. There were no codes present to indicate a malfunction; this was just preventative maintenance. The "upstream" oxygen sensors are the 2 (of 4 on the Escape 3.0 V6) that are in the exhaust system prior to the exhaust reaching the main catalytic converter. These provide feedback to the PCM (computer) that adjusts the air/fuel mixture and affects how the vehicle runs and also the emissions. Oxygen sensors wear out and when they do they can result in lower fuel mileage and higher emissions. I purchased the Denso brand replacements from Rock Auto.

Here is what I learned, I hope it helps someone:
- When listing oxygen sensors, all of the parts catalogs and the illustrations above refer to "front", "rear", "left" and "right". "Front" refers to the 2 sensors that are in the exhaust stream prior to the catalytic converter (i.e., "Upstream"). These are the ones I replaced. "Rear" refers to the 2 sensors that come after the catalytic converter in the exhaust stream. ""Left" and "right" however are misnomers to the average shade tree mechanic. When you get under the vehicle, because the engine is mounted transversely (side to side), there is one sensor in front of the engine and one behind it. The one in front is the "left" sensor and rear one is the "right" sensor.
- Although both sensors are visible and easy to get to from underneath, the wiring and the connectors are hidden behind the plastic splash shields. To have full access to the wiring, you must remove both the left and right splash shields (the ones that go across the front of the vehicle and then into each wheel well).
- The illustration posted shows a special tool to remove the sensor. I did not need to use it. Instead, the sensor can be turned with a standard 7/8" combination wrench using the open side. The front/left sensor, perhaps because it was in area of less heat, was easy to unscrew and remove. The right/rear sensor was a completely different story. No amount of rust penetrant and/or knocking the end of the wrench with a hammer made it budge (and it started to round off the edges of the sensor too). I decided that I needed to use the closed end of the wrench to try it where it couldn't slip. The problem was that even after disconnecting the wiring, the wiring was too big to fit through the ring of the wrench (which was needed to get the wrench down to the sensor!). Since I didn't want to destroy the old part (in case the new one didn't work and I needed to reinstall it), I ended up clipping the plastic retention clip part of the wiring connector which was what was blocking it from getting through. There were two other clips on this sensor wiring that were removable so I took them off too and the wiring could now fit through the wrench. Finally with the closed end of the wrench around the sensor and some VERY healthy hammer blows, I was able to remove it.
- The new sensors came with a small vial of high-temp anti-seize lube, so no need to buy any extra (in fact one vial was good enough to do both new sensors).
- The new sensors screwed in just fine, but the illustration says to tighten them to 40 Nm (30 lb-ft). I have no idea how to do that with a wrench (my torque wrench is set up for sockets), so I just tightened them quite tight by hand (and I could "feel" the new metal washer compress). Good enough for me.
- At least in the Denso brand, the right/rear sensor wiring was WAY TOO SHORT! I had to remove the vehicle wiring connector from where it was attached and stretch it way over to the new sensor connector. Then I had to jerry-rig it in place with zip ties so that it didn't move and come in contact with any of the moving parts down there (the axle is really close by). It was doable, but just be aware of this issue with the Denso part.
- No noticeable difference in how it runs, but then I didn't expect any since it was running great before the swap.
 
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