Replacing a Downstream Oxygen Sensor

I replaced the Downstream Oxygen Sensor (Bank 1, Sensor 2) with a Bosch 15733 0258986602.  This universal 4-wire replacement sensor came with a kit that allows it to use the existing harness connector from the old sensor.

There is only one bank of sensors on the four cylinder vehicle.  The first sensor is the upstream one, or the one in front of the catalytic converter.  I had to replace the downstream one.

The first step was locating the sensors.  Opening the hood, you can see both sensors to the left of the engine.  [Here, it's just to the right of the red-box-looking area.]

And zooming in...

Mercedes provides a special tool for removing the sensor - it's something like a crow's foot, offset, open socket.  For this repair an adjustable crescent wrench was used, though it was difficult to apply enough torque in the limited space.

To access the wiring harness, the vehicle had to be raised.  The plastic undercarriage panel below the sensor was removed.  The sensor wires were removed from the retaining clips.  The wiring harness was located on the opposite side of the engine.

An awl was used to depress the nubs on the wiring harness in order to separate it.  Here, an arrow points to a triangular indentation that is not visible from this perspective. 

The wiring harness connector was attached to the replacement sensor using the supplied kit.  Bosch recommends not soldering on a new connector - likely because of the heat involved.  Installation was straightforward.  

Here, the new and old sensors are compared:

Car

Cars are great... when implemented with moderation.

The first car that I sought out, and enjoy owning (I wouldn't say that I enjoyed owning the Maryland Messenger) is a Mercedes C230.  It truly is a fancy, safe, economy car.  One drawback, however, is the cost of repairs.  So I'll try to document them here.

Car:
2004 Mercedes C230 6-Speed Manual Hatchback
4-Cylinder
Style W203

Issue: Interior blower fan won't blow
The fan stopped working intermittently, and then stopped turning on altogether.  The air conditioning compressor seemed to still be making noise, so I narrowed it down to the fan.
Checking the fuse box located to the left of the steering wheel (hidden behind a panel that you can find with the drivers door open) I found one fuse to be quite charred and melted.  I replaced the fuse with one of the same, proper amperage, and it's worked flawlessly since.  What exactly caused the fuse to get all melty, who knows...  Corrosion on the blades
 may have affected it.
Cost:  $5

Issue:  Very Slight Evaporative Emission Leak.  P0442
This comes from a very slight leak detected when recycling unused fuel.  Various forum discussions suggest it's not from a loose cap (which would be a large leak).  Mostly likely cause is a faulty Evaporative Purge Vacuum Solenoid.  The OEM part was around $200.  I replaced the valve with a used one on Ebay for $25 which did not solve the problem.
The part I replaced was manufactured for a different different vehicle, so I had to slice off one of the alignment keys on the wire harness connector.
On a hunch, I added a couple of hose clamps to the hoses adjacent to the valve (where there were none, previously) which did solve the problem.  It seems that wearing of the rubber over time, in addition to the changing temperatures, may have contributed to some leaking from around the press-fit connections of the rubber hoses.
>>>Update 2015-06-05<<< As it turns out, this code was being thrown because of a difficult to diagnose crack in the fuel filler neck.  A smoke test did not reveal it.  Charlotte Star Services (Charlotte, NC) eventually identified the problem and repaired it for a nominal fee.
Cost:  $??

Issue:  Oxygen Sensor Heater Bank 1 Sensor 2.  P0141
This popped up right after correcting the Emission Leak, so there may be some kind of relation.  The error thrown refers to the 'downstream' oxygen sensor.  In a 4-cylinder car there is only one bank.  Sensor one is the sensor before the catalytic converter and sensor two is located after the catalytic converter.
The price of the OEM component is three or four times as much as a generic component, so I decided to try the basic first.  Here I describe how it was done.
Cost:  $50

Time

"Time.  What is time." - favourite computer vision professor Neils Lobo