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Upstream O2 Sensor Test Confusion... Please Help!

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Upstream O2 Sensor Test Confusion... Please Help!

Old 04-14-2019, 07:34 PM
ldzoller is offline
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Location: Virginia
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Default Upstream O2 Sensor Test Confusion... Please Help!

First post. Been a lurker for a long time.
I am trying to determine if my upstream O2 sensor is beginning to go bad. I use the Torque App with a generic OBDII bluetooth scanner. It shows the voltage of the upstream sensor. I think it shows 4 frames per second, so I assume it refreshes at about .25 seconds.
Anyway, the voltage is not a nice, consistent variance between +/-.1v and +/-.9v, which I would expect. The readings I get make no sense. Sometimes it reads .2v and sometimes it goes up and down like it should. However, it never gets above .7v.
I tried injecting propane into a vacuum hose to simulate a rich condition (off brake booster). The sensor would spike at .9v everytime, but not stay at .9v, no matter how long I injected the propane.
Do these results condemn the sensor? Any other ideas of tests I can run?
BTW, the truck is a 1999 Ram 5.9L with 161K miles. It has the original cat but these are not original O2 sensors. Kegger modded, throttle body ported, Hughes plenum gasket kit, otherwise stock.
TIA for any help!
Old 04-14-2019, 07:51 PM
Torxhead is offline
Join Date: Oct 2011
Location: Yorba Linda,Ca.
Posts: 179

Well, that sounds just like an O2 sensor is supposed to operate. When it slows down the changing voltage or not at all then it is time to replace it. My '99 V10 still has all of the oxy sensors still operating. I check mine with a digital volt meter.
Old 04-14-2019, 08:22 PM
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HeyYou is offline
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Location: Clayton MI
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Sounds like it is working as advertised. The the sensor sees the rich condition, the pcm will pull fuel. You should be seeing short term fuel trims going down at the same time. However, if you have over 100K miles on it, probably time for a new one. NGK or Denso please, skip the bosch. Our trucks don't like 'em.

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