1) Check the resistance of the oxygen sensor heater: Use an ohmmeter to measure the resistance between the oxygen sensor socket terminals (heating resistance). The adjacent wires drawn out by the heating resistance have the same color, making it easy to distinguish. The cold resistance is about 4 ohms. (There are four wires in total for the oxygen sensor, arranged in a straight line, with one pair connected, which is the resistance end; the other pair not connected, which is also not connected to the resistance end, which is the signal output end)
If it is detected as an open circuit or the resistance is not within the normal range, the oxygen sensor needs to be replaced; If the resistance value is normal, proceed to the next step of troubleshooting.
2) Check the power supply voltage of the oxygen sensor heater:
Turn on the ignition switch and measure the voltage between the oxygen sensor plug (harness side) terminals corresponding to the heating resistance end, which should be the battery voltage.
If the voltage is low or none, check the wiring from the oxygen sensor plug to the injection relay and ground.
3) Test the ground insulation of the oxygen sensor resistance heater: Use an ohmmeter to measure the resistance between the oxygen sensor resistance heater and the housing, which should be ∞.
If there is a pathway, replace the oxygen sensor. If there is no pathway, proceed to the next step of maintenance.
4) Check the signal voltage of the oxygen sensor:
① Disconnect the 4-pin connector on the oxygen sensor with the ignition switch turned off;
② Connect the 12V power supply of the battery to the resistance heating end of the oxygen sensor. This method requires making a pair of wire connectors, namely testing fixtures. After connecting, start the engine and measure the voltage at the signal output terminal after 2 minutes.
If you think the operability of this method is not strong, you can start the engine directly. After 2 minutes, unplug the four pin connector and quickly measure the voltage of the oxygen sensor signal terminal. (After a long time, the core of the oxygen sensor will cool down and the measurement error will increase after the heating resistor is disconnected from the power supply) (I used the second method)
In the idle state after starting the engine, according to the above working principle, the output voltage should be very low; At this point, increase the throttle. At the moment when the throttle changes, there will be a voltage output that is related to the rate of throttle change (i.e. the voltage will disappear immediately when the throttle is stabilized), and the voltage will increase as the throttle changes. The maximum value can reach 0.9V. If it is a pointer meter, due to inertia and damping factors, this voltage can generally only be read at 0.8V. (Considering the response time of a digital meter, it is not possible to measure it with a digital meter, otherwise the error will be significant.)
If the oxygen sensor has no voltage output, the voltage value remains unchanged, the voltage rise or fall is small, and the voltage change is slow, it indicates that there is a problem with the sensing element of the oxygen sensor. At this time, cleaning the oxygen sensor can be considered.