Hello,
I'm driving a 1998 4wd blazer, 4.3 engine. The truck sometimes hesitates when the ECU transitions from open to closed loop mode. I used a scanner capable of recording and graphing sensor data, fuel trim, etc and it appears that the bias voltage supplied by the PCM to the bank 2 o2 sensor is 1.105 V. The two other sensors- post cat and bank 1 sensors have a bias voltage of .440- which is correct from what I read.

When the ECU transitions from open to close loop mode, I believe the computer thinks there is an overly rich condition and tries to lean the mixture- the short term fuel trim for Bank 2 sharply drops to -30.5% causing hesitation. After hesitating for about 5-10 seconds, the output voltage of the sensor appears to behave normally and the truck runs fine. (Fyi this has caused a PO300 random misfire in the past)

I guess my question is would a faulty o2 sensor cause a high bias voltage or would the PCM be at fault. Also, which side is Bank 2? left or right (sitting in drivers seat)

Thanks,
Joe

 

I think it's on the right. Since you can see them ranging disconnect it and start the truck, when you see it quit ranging on the scanner you're certain you have the right one disconnected. PO152 explained This will explain how to check it out.

 

you could also swap the O2 sensors B1 for B2 and B2 for B1 and see if the problem follows to B1, if it does its likely that the O2 sensor is at fault... if it does not follow, it could be in the wiring

 

Success! I unplugged the connector and the terminals were green with corrosion. Cleaned the plug terminals with electrical cleaner, a small wire brush, and compressed air. Ran to Advance and picked up a new sensor. Then I applied a small amount of die-electric grease to the terminals and rubber seal. So far the voltages look good and the truck runs and idles well. One thing I noticed is the plug sees a lot of water from the A/C. I repositioned the plug so it doesn't get drenched with water every time I use the A/C

Thanks for all your help!

 

Glad to hear you got it fixed!! now others may learn from this if they have a similar problem