![]() ![]() A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). That same wire if disconnected from the O2 sensor will read 5 volts constant to ground.Īt idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. The O2 sensor is an O2 concentration sensitive variable resistor. The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor. Loss of that power will hurt gas mileage even with a good O2 sensor. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immedietly after start up. I hope to use this post (thread) as an FAQ about how to properly test mounted jeep O2 sensors and the wiring and related hardware.įor the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. ![]() This question comes up a lot in threads with O2 sensor trouble codes and threads about bad mileage. ![]()
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