Why can't I use the heater circuit on my 4 wire O2 sensors to test for my .1 to .9 vdc and using an infared thermometer they only get to a max of 195 deg. on the surface.

The old sensor heater circuit ohm's are 5.1 and the new are 6.0 ohm's. I connect 12.2 volts to both heaters and neither will generate even .1 volts.

Everything I find on line to bench test uses a propane torch to get them hot, it seems like we should also be able to just use the internal heater.

Any thoughts would be appreciated. BTW these are for a 2000 Blazer

 

The heater doesn't get anywhere near hot enough. It's designed to help the sensor heat up faster. The quicker it heats up, the quicker the PCM goes into closed loop operation.

 

Seems like I remember reading somewhere that the heater supposed to get it up to 600 + deg.

I guess I'm a little confused, I watched a video about the AEM UEGO O2 sensor tester and all they do is plug in the sensor and wait a few moments and the UEGO tester gauge starts reading either lean or rich depending on if the sensor is open air or sensing a flammable compound.

 

They may have exposed the entire sensor, (including the reference passage) to flamable fumes and bench tested it, (essentially removing all oxygen). Testing like that will indicate a lean or rich condition and does not require the sensor to be heated nearly as hot. The sensor is literally doing as its name implies, "sensing oxygen" or the lack of it in this case. There are some youtube videos that show how to test using propane, which is a little more accurate. Neither method will test reaction time or crossover counts, two equally important functions of the sensor. The sensor tip needs to be in the exhaust stream to be tested thoroughly and accurately. It needs to be heated sufficiently both actively by the heater, and passively by the exhaust. The heater alone might produce 200F, and it's not designed to be the sole supply of heat, it simply helps the sensor heat up faster so closed loop can be achieved sooner.

Each time the engine is started, the PCM controls the engine in open loop operation. During warm up, the PCM monitors data from the MAP, MAF, TPS, & ECT sensors and ignores data from the oxygen sensors. It then calculates and applies the necessary fuel injector pulse width, ignition timing, etc. When engine coolant reaches a certain temperature and the oxygen sensors start producing voltage, the PCM switches to closed loop operation. The PCM then uses the O2 sensor data to monitor the actual fuel mixture and adjusts it accordingly. Coolant temperature at start up is the determining factor when it comes to how long it remains in open loop: If coolant is at operating temperature when the engine is shut down, and then restarted immediately, the PCM will usually switch to closed loop within a few seconds, basically long enough to bring the oxygen sensor back up to temperature.

 

Thanks for the info. I've been working on my trouble codes for awhile now and must say I've learned a lot. originally, code was PO153 so I purchased a new (generic I guess) because it has no numbers or info. on it sensor. Installed and then code changed to PO154. So, then I swapped the front two sensors and now I get a code PO134 so I guess this is telling me I have a bad new sensor. After reading on this forum I think I'll buy only AC Delco or anything but Bosh.

The car runs perfectly, even with these codes popping up and it has 115,000 miles. Have not had one electrical problem until this code issue. Wish I could say that about everything else on it. Far too many problems I've had to correct to list here in the 8 years I've owned it. But as long as it keeps running good, I'll keep it.

 

P0153 is indicating the passenger front sensor has a slow response time. With 115K miles, no surprise there, time to replace it.

P0154 is indicating no activity from the passenger side front sensor. Probably a faulty sensor.

P0134 is indicating no activity from the driver side front sensor. Confirms a faulty sensor! Good job.

EDIT: I've used Bosch sensors, and what I have noticed, is the crossover counts are slower than "ideal". The faster the reaction time, the better the fuel mileage will be. AC Delco is a good choice when it comes to O2 sensors.

 

Thanks, I'll post the results when I receive and install.

BTW Amazon has the AFS105 for $30.47 compared to $118.00 at my local parts house!!!!

Dave

 

To follow up on my problem. Installed two new A/C Delco sensors this morning. Cleared the codes before starting the car. Watched the sensor outputs with my scan tool and before I got out of the driveway they were already switching. The other off brand new ones didn't start switching until I drove at least two miles and by that time it was too late, it listed a fault.

Amazing to me that the A/C Delco started switching so fast..... I guess what they say on these forums about Chevy only likes A/C Delco is correct.

Thanks for the help. Now onto finding out what's causing my PO452 code. I know it's evap. press. too low but need to find out why.

Dave

 

Seeing is believing when it comes to AC Delco parts. They heat up faster and switch from lean to rich & rich to lean faster as well. Both contribute to better fuel economy and performance.

Here's the link for diagnosing the P0452. It's straight out of the GM shop manual:
https://blazerforum.com/forum/diagno...plained-35142/

EDIT: You'll need a vacuum gauge capable of reading inches of water, not mercury.