I need some help with this... Its got me stumped.

Truck is 1998 Suburban 5.7 4wd with 166,000 miles. It runs perfect. its new to me so I have no history.

I am getting a reoccurring code PO137 Bank 1 sensor 2 low voltage... it reads ZERO volts while driving... and around .4 at idle.

Scanner readings show it working at idle... but it drops to
zero Volts at cruise... Accel stays at zero.... but when I let off the gas it will jump up briefly to around .450V and drop back to zero.
I switched the sensor with the other side expecting the problem to follow and it did not.

Short term and long term Fuel trims for both sides are excellent and nearly the same... Engine runs great.

I the left side Cat off and it appears to be clear and complete. There are no indications of exhaust leaks at all. I am in proess of replacing the cat with another and I will retest.

I am thinking its an electrical issues... can anybody direct me to anything specific? Where does that sensor ground?

Thank you for any help.
Reaney in NH

 

Did a cursory search. It would seem the O2 sensor grounds through the black wire to the PCM (B-3), and there's also a 5V reference and signal line (grey/F-14 and dark blue/A-15, respectively, according to te source I found: Part 1 -Testing the Oxygen Sensors (GM 4.3L, 5.0L, 5.7L)

Definitely seems electrical if the cat isn't clogged and the problem doesn't follow the sensor. check your pins for cleanliness and wires for damage. Continuity would be where I'd start.

And you are moving the downstream sensors, right? Not the upstream ones?

 

Thank you for the info

Yes... its downstream or Post Cat sensors.

When I resolve this I will post the results to help others.

 

So there is a cat involved in the exhaust right now? What I would do is plug everything in as it should be normally, and install your multimeter on a low scale and back probe the connector and take a reading right at the 02 sensor. Your multimeter will show you the same milivolts that the scanner will. High milivolts indicates running rich (700mv+), low milivolts indicates lean, or a slow/lazy o2 sensor (100mv+/-)

by taking your measurement right at the 02 sensor, you're testing to see if the computer is capable of reading the same reading as you get right at the 02 sensor. If the readings are different between your multimeter and the scanner, that would mean that there is most likely a wiring problem going from the 02 sensor to the computer.