cueball

does anyone know how the O2 SIMs work,or what is in them, i know how the O2 sensor works
so i have an idea how O2 SIMs work
i just want to know for sure
thanks! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Camaroholic

iTrader: (1)

Yep. O2 sims have a small circuit inside of them that slowly drifts them around .45 volts, above and below. They contain a small battery that powers them. Eventually, they will die.

I believe there was a recent design discussion on the LT1Edit mailing list (at http://www.lt1edit.com ). Maybe a search of recent archives would give it.

-Andrew

cueball

wy dont they just tap into the 12V. heater circuit and put in a capasiter and some resistors
to power the O2 sim,
does the O2 sim fluctsuate around .45V
or is it constant?
if it was constant between .3V -.5V
will it set a DCT code?
thanks

ToplessTexan

If it doesn't oscillate it'll throw the insufficient activity code. It's doesn't have to move much though, just out of the bias voltage window.

cueball

how did you check that, did you take a vo.ohms metter across the A and B wires,which one was pos. and neg.?did it osillate voltage,
if it stayed at .35V or .5V it set a code?
sorry for the Q. just tring to get a better understanding <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
thanks!

WJ SOM SS

iTrader: (11)

What is the traditional lifespan of a pair of 02 simms? Thanks. WJ. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

jaywoo

I have a write up somewhere on this. They don't use a battery, they use a capicator that charges and discharges off of the 12V input. Runs through a resistor or two. If I can find that article, I'll post it.

jaywoo

Found it. I didn't wirte this, found it on another auto forum:

A properly functioning oxygen sensor will exhibit a rapidly fluctuating voltage signal alternating between approximately .2 and .8 volts in response to varying residual oxygen content in the exhaust stream. Look to your scope's time reference line for a desired lean-to-rich and rich-to-lean time of less than 300 milliseconds. A response time greater than 300ms. means that the sensor should be replaced. It is important to recall that these values are valid only when checking a sensor operating in "closed loop" in a hot exhaust stream (350o-8OOoC). Sensor age degree of contamination, mixture setting, and exhaust temperature all have an effect on response time.

It has to oscillate roughly 1/2Volt in .3 secs to be a good sensor. You need a cap/resistor to do this. f=1/RC and f=1/time -> time=RC -> C=time/R, so pick a 1kOhm resistor and you'll need a C=0.3/1000 = 300uF. We need it to be faster than .3secs, so just get a cap that's smaller than 300uF (200-250uF should work fine).

The resistor is between the signal wire and the O2 sensor and the capacitor attaches between the signal wire and ground

eallanboggs

iTrader: (1)

I ask this same question numerous times myself here, but no one seemed to know or cared to post the answer so I answered the question for myself today. I installed the O2 Simms and then connected the scan tool. The output oscillates between 0.435 VDC and 0.735 VDC about once a second. The voltage goes up slightly to say 0.835 VDC and back to 0.435 VDC under acceleration bacause of the slightly higher BATT voltage due to the alternator output. That proves it doesn't use on INTERNAL battery for the source voltage. This output is EXACTLY what the PCM is looking for from the post O2 sensors so the O2 Simms should work quite well in fooling your PCM into believing you have functioning cats. I've never seen a schematic for the O2 Simms, but it works like an R/C circuit. They work!

cueball

thanks for the info guys
it helped out a lot.