2001 2.9L: Cannot read voltage from upstream O2 Sensors

[DanSC]

Hello,

For context, my 2001 2.9L S80 presented with P0422 and P0432; catalytic converter efficiency below threshold for both cylinder banks. Then an O2 failure code appeared, I changed the sensor, and the problems dissapeared. More details in this post: viewtopic.php?f=11&t=85269

Since then, the car easily passed a California smog check.

Now the P0422 and P0432 codes have reappeared. However, my OBD2 scanner (Bluetooth adapter + Torque App) displays the downstream oxygen sensor voltages, but not the upstream sensor voltage. The voltages are not zero; the app does not detect any kind of signal. Otherwise, the car runs and drives normally, including fuel economy (around 20 mpg city; 28 mpg highway per instrument cluster display).

This is not normal, correct? Or does the car not report the upstream oxygen sensor voltages by design?

[SuperHerman]

I may be wrong, but the two codes point to a failed/failing cat.

Try unplugging the front two O2 sensors and see if you get a different code - specifically one stating the O2 sensors are not there. It appears your car's computer is seeing the O2 sensors, but is not happy with the data they are receiving.

As to your App issue, you may have the wrong items selected. On one of my Apps if you select the wrong item to read it will behave as you mention - yours may be smarter than mine - just throwing out something.

[RickHaleParker]

That car has two catalytic converters. Both codes are for Three-way catalytic converter (TWC) efficiency (One each). The odds that two cats fail at the same time or a O2 sensor failed on both sides at the same time is slim.

These codes can be trip by just about anything that messes with the Air/Fuel mix ratio or burn efficiency. Replacing the catalytic converters should be the last resort. Next to last is O2 sensors.


Possible source

• 1. Misfiring
  2. Air leakage in the intake system
  3. Air leakage in the exhaust system
  4. Faulty fuel pressure
  5. Uneven compression
  6. Defective three-way catalytic converter (TWC).