1997 Dodge Dakota

I got a po 132 code "o2 sensor circuit high voltage" replaced o2 sensor twice. Checked vaccum lines on throttle body. Started trouble shooting, when I reset the code and disconnect o2 sensor and run the truck with 02 unpluged same code comes up. There doesn't appear to be any frayed wires. Kinda stuck need some help.
March 26, 2011.

The O2 sensors can't generate a voltage much higher than 0.8 volts. To get that code is almost always due to a wiring problem as in the signal wire and the 12 volt heater wire are shorted together. The easiest way to figure this out is to connect a scanner that can read live sensor data. View the signal voltages for all of the sensors to be sure you're working on the right one.

Mar 26, 2011.
Ty turns out that the ground to the upstream o2wireharness was broke off up at the engine. The reading on the out put was 4volts when I located ground and fixed got a reading of.1 to.8 this varied. Check engine light has been off since. For future refrence, on a heated o2 sensor could you splice ground off at the harness and ground it to the frame by the upstream sensor.

Mar 27, 2011.
The heaters are already grounded to the body so that wouldn't be an issue, but the sensor circuit can not be grounded. They go to ground through a circuit in the Engine Computer. That's how it can measure the integrity of that circuit. All four O2 sensors are grounded on the same pin so I don't know what would happen if only three made it back there and you had one sensor grounded on the body.

As for the 4 volts, there are two possibilities. With other sensors the computer uses "pull-up" resistors on the various sensor circuits. They are so high in value that for all practical purposes they aren't even there, but when there is a break in the circuit, the computer will see the voltage coming from that pull-up resistor. That forces the computer to recognize a defective value and set a fault code rather than allowing the voltage to "float" around at some random value. Normally the computer will see full battery voltage or 5.0 volts from the pull-up resistor. The point is it won't have to guess or be confused.

The second possibility is that 4 volts was indeed some random value coming from other circuitry in the computer in the absence of a strong proper signal from the O2 sensor.

My guess is it set the "voltage high" code, which there was no arguing with, instead of an "open O2 ground" code because it was still seeing the ground current flow from the other O2 sensors. It would likely have set an open ground code if the ground wire was broken before the splice where it branched off to all of the sensors.

Happy to hear you found the problem.

Mar 27, 2011.