Universal O2 Sensors
 

I am planning to replace all four O2 sensors on my C43. The Bosch universal part# for all, before and after CAT, is 15738. My question is, are the sensors all the same. How come Bosch has separate part#'s for all four, 15088, 15090, 15092, 15094. I know that the universal needs to be spliced, but other that that, what's the difference? The universals are much cheaper.

Why replace the rears? They don't do anything for the cruise A/F ratio... they're only for cat efficiency.

Once you find an answer for your orig question, let me know what purpose replacing a non-faulty o2 sensor serves. Mine are original and I was thinking of doing the same, but not sure what kind of situations it would improve/remedy

The ONLY difference ON THAT car is the length of the wires.

The actual sensor is the same foe all 4 locations.

I replaced two of the four on my wife's Expedition. I used universal ones with different part numbers and the only difference was the length of the wires. It didn't matter anyway as I used some of the wiring from the old sensor.

I was told that an O2 sensor will start to go bad slowly until a code is sent. If your O2 sensors have over 75,000 miles I bet they can be replaced and you will see results.

O2 sensors are considered Maintenance items.
As they get old, they tend to move slower & slower, i.e. the transition speed between lean/rich slows down.
This can result in a reduction of fueleconomy.
I'm well aware there are people that would not consider changing these, until they see the Check Engine light on. ;)

my 02 sensor in the 88 260e was causing the light to come on about a mile down the road. it would then go out shortly later.

i noticed my highway mileage had dropped to 19. changed the sensor with a universal. highway mileage now back up to 24.5

If you look around, you may find sensors considerably less-expensive than the "universal." I have not tried this with 4-wire sensors, but for the single-wire type used on 380's and 560's, I used a sensor for a '90 Mustang. IIRC, the universal were like $35, and the Mustang less than $20. You just cut the end off and supply your own connectors and heat shrink.