o2 Sensor Testing Question

I pulled all 4 o2 sensors off of my 1996 Blazer because I was receiving a P0420 and wanted to check the sensors before testing the cat.

Two of the sensors were reading 3.6 ohms,
another 4.5,
and the fourth was 5.8

I also tested them by heating with a hand held propane torch. All of them reached .9xx volts and within seconds of removing the heat the voltage would drop to .01 volts or lower.

The question is could the sensor that was testing at 5.8 ohms be bad? From the information I received during research is that the sensors should be between 3 and 4.5 ohms. If there are any other problems that you may notice please feel free to let me know!

Thanks in advance.

Your voltages seem right which is what the computer reads, however it will compensate for some wear.

However did you check the O2 sensor for steady voltage while heating for two minutes?

and have you tried swapping them to opposite sides of the cat to see if the code comes back?

I also had that code come up one time based on a dirty MAF.

Hope that helps

-Mark

I pulled all 4 o2 sensors off of my 1996 Blazer because I was receiving a P0420 and wanted to check the sensors before testing the cat.

Two of the sensors were reading 3.6 ohms,
another 4.5,
and the fourth was 5.8

I also tested them by heating with a hand held propane torch. All of them reached .9xx volts and within seconds of removing the heat the voltage would drop to .01 volts or lower.

The question is could the sensor that was testing at 5.8 ohms be bad? From the information I received during research is that the sensors should be between 3 and 4.5 ohms. If there are any other problems that you may notice please feel free to let me know!

Thanks in advance.
You can read out 02 sensor voltage with a good volt meter.
Or switch sensors around.
But
The only way to test out sensors and cats is with a engine capable scanner read out on what sensors and cat is doing.

DTC P0420 - The down stream H02 sensor signal on bank 1 told the ECU, that the catalytic converter isn't doing it's job.

99% That the cat is burned out.

1) Tap on the cat on bank 1 with a hammer and compare the sound with the cat on bank 2.

See OE Cats @ http://www.catalyticconverterwarehouse.com

I was almost certain the cat was burnt out because I did start to hear a little rattling coming from it. I just want to make sure the sensors are good because I did have a bad misfire not to long ago and would like to solve the issue asap.

Did the Misfire turn into a backfire?
A rattle tells me the cats broken, and a empty tin can sounds like the the cat is blown out.

I was almost certain the cat was burnt out because I did start to hear a little rattling coming from it. I just want to make sure the sensors are good because I did have a bad misfire not to long ago and would like to solve the issue asap.

Misfires and engine running problems are usually the cause of cat problems.
If you replace the cat make sure you repair the engine running and misfires problems or the cat will burn out again.

Cat rattle can be lose stuff inside cat or heat sheild rattle.

Cat not working or bad 02 sensor can cause 420 cat codes and also bad running engine problems.

Engine not running right is the main cause of cat failing.

Good Luck and let us know how it goes.

I fixed the misfire a month or so ago. Ended up replacing the fuel injectors (had 225,000 miles on them) and the only code that was remaining was the p0420. A couple of days ago I bought two ac o2 sensors because there were two that were in very poor condition and didnt test correctly for voltage. I put the two new sensors in the y-pipe and reset the ecm. The ses light came back on within 50 miles and I checked the heat shield and found no visible problems. I pulled the cat off and replaced and the vehicle runs/accelerates much smoother than it did with the old cat on. Will post back if any codes return! Thanks for the help everyone.

I fixed the misfire a month or so ago. Ended up replacing the fuel injectors (had 225,000 miles on them) and the only code that was remaining was the p0420. A couple of days ago I bought two ac o2 sensors because there were two that were in very poor condition and didnt test correctly for voltage. I put the two new sensors in the y-pipe and reset the ecm. The ses light came back on within 50 miles and I checked the heat shield and found no visible problems. I pulled the cat off and replaced and the vehicle runs/accelerates much smoother than it did with the old cat on. Will post back if any codes return! Thanks for the help everyone.

You are welcome
And good Luck.

Thanks for posting back with your diagnostics and solution!