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Negative voltage from O2 sensor?
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mangomills Offline

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Joined: May 2008
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Post: #1
Sad Negative voltage from O2 sensor?
I just installed a dual efie (plastic coated) to a 2003 GMC sierra 4x4, 4.8ltr. with HHO. Testing the connection showed the efie on both banks adjusted to .2volts. Good. However, the O2 sensor on the left bank is showing 0.02-0.03 volts with a total voltage going to the cpu of 0.11 volts...??
The right bank shows the O2 sensor output as negative 0.2 volts, steady. The total showing 0.00 volts (makes sense).
The voltage going into the efie is 13.05. The ground is okay.

I connected the wires close to the sensors, the left bank wires are connected to the actual wires off the sensor while the right bank wires are connected to the wires just after (toward the cpu) the sensor wires connection. Hope that makes sense.

The vehicle is running Open loop and now getting codes P0134 and P0154.

Any suggestions?
06-20-2008 07:36 AM
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mike Offline
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Joined: Jul 2007
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Post: #2
RE: Negative voltage from O2 sensor?
Something is quite odd here. .2 volts negative is not correct as an output from the oxygen sensor. You should be getting positive voltages from both sensors, and those voltages should be changing rapidly in the range of .3 to .8 volts or so. It could be more or less, but the average will be plus .45 (but you won't be able to place the average that precisely). The EFIE will add .2 volts on top of that, so if you measure the white wire to ground, you'll get the same values but shifted up in voltage by .2 volts.

Please disconnect the EFIE, temporarily re-connect the sensor to the ecu, and measure the sensor's signal wire to ground. Do this on both sensors.

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06-20-2008 08:08 AM
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