I have been doing some research on O2 sensor types because the common practice of putting rears in the front of header equipped cars puzzles me. I guess I want to know why it works. So far, I still don't know but am just getting going.

I'm also puzzled by what I got when I bought new GM fronts that have lower heater current than the originals. What I have posted below might give some insight. I believe these may be the new planar style sensors.



Thimble Type Sensors

So called due to the design of the ceramic sensor element used. These
sensors can be constructed in various formats from simple single
wire sensors to heated four wire sensors with either ground isolated
or grounded cases. Using a patented “Platinum Grid” design thimble
these sensors are manufactured in the following formats:

Single Wire Sensor - the original design, sensor output voltage via
the single pole connector, grounded via the sensor body.

Two Wire Sensor - for improved earth reference of sensor output signal,
a reference wire is also connected between control unit and sensor.

Three Wire Sensor - heated sensors provide various advantages including,
q Earlier cut-in for closed loop operation
q Lower emissions with new and aged sensors
q Lower sensor deterioration caused by thermal stress
q Extended service life (from ~ 50,000km to 80,000km +)
q More accurate fuel management system calibration
q Greater flexibility in sensor location

Bosch manufactures heated sensors with either 12 or 18 watt ratings for correct sensor operation during warm up and the complete vehicle
drive cycle.
Note: Use of a sensor with an incorrect heating element rating will result
in overheating of the sensor measuring element causing the
thimble to fracture.

Four Wire Sensor - heated sensor with integrated earth
reference/supply circuit, these sensors may be either grounded
through the body or earth isolated depending upon engine management
system design and customer requirement. Earth isolated sensors are
provided with an earthing circuit for the measuring cell by the engine
management control unit. The engine management control unit
purely references the earth of a sensor that has its body grounded.
Note: mis-matching of body ground/isolated sensors can result in the
signal earth being open circuit causing the sensor signal to not be
recognised by the engine management control unit.

Planar Type Sensors

Improved designed sensor using “Planar” or thick film manufacturing
technology. These are heated four wire sensors and whilst operating
on the same principle as the thimble type sensors, the planar design
provides a more effective heater design, more robust construction,
faster switching time and superior service life.

This info comes from Bosch and can be found here:

http://www.bosch.com.au/content/lang.../Section_A.pdf

BTW, from my measurements, our Vettes have 12w heaters stock, and are for sure thimble type sensors. Interesting about the 18w unit, might be a fix for header equipped cars.

Interesting reading.

Ron

 

for what its worth both my tuner (speedinc) and Tony at ARH stated theres no reason to use the rear o2s in the front positions

 

Cool info!

BC

 

Makes sense to me. But folks do it, say it works, and have no clue as to why.