Agree with previous answer. Get and OBD scanning tool to try and identify which one it is. Then perform the following:
- Identify the specific o2 sensor that you want to do the oxygen sensor test on. Depending on the year of your car there could be up to 5 o2 sensors located along the exhaust system. Fortunately, the computer DTC will pinpoint the specific o2 sensor that needs to be tested. Using the DTC, you can refer to your owner’s manual to locate the sensor. Your owner’s manual will also identify the signal wire as many o2 sensors have multiple wires connected to it.
- You will need a 10-megaohm impedance digital voltmeter for testing the o2 sensor. You should set it to the millivolt (mV) DC scale.
- Now start the car and let it run until it reaches operating temperature. This may take up to 20 minutes.
- Once you have reached operating temperature, turn off the engine. Now connect the red probe to the o2 sensor’s signal wire and the black probe to a good ground. Please use caution when connecting the probes as the engine and exhaust system will be extremely hot.
- To perform the actual test, start the car again and check the voltmeter’s voltage readings. The o2 sensor’s voltage should fluctuate within the 100mV – 900mV (0.10V to 0.90V) range. If it is within this range, the o2 sensor is operating normally and you can stop testing. In case it is not within range, there is either an engine problem (loose hose) or the o2 sensor is bad. If it appears to be bad, continue with the next steps.
- Test the o2 sensor response to a lean fuel consumption situation. Disconnect the hose from the positive crankcase ventilation (PVC) valve which is located on the valve cover. This will allow more air into the engine so the voltmeter should read close to 200mV (0.20V). If the voltmeter does not respond, the o2 sensor is not functioning properly.
- Reconnect the PVC hose to test the o2 sensor’s response to a rich fuel consumption situation. To do this disconnect the plastic hose connection to the air cleaner assembly. Block the hose connection opening with a rag in order to reduce the amount of air going into the engine.
- Check the voltmeter. It should read close to 800mV (0.08V) due to the reduction of oxygen entering the engine. If the o2 sensor does not respond this way, it is not functioning properly.
- Reconnect the hose to the air cleaner.
- If the o2 sensor responded correctly to the lean and rich fuel tests, another component could be causing the problem. The potential issues could be a vacuum leak, ignition system or something similar. Obviously, if the o2 sensor did not respond properly then it is bad and will need to be replaced
As to the speedometer/odometer, sounds like a possible issue in the connection between the vehicle.speed sensor (VSS) and the dash cluster. Make sure connections are secure, not corroded, and if need be, disconnect from.cluster and sensor, and do a continuity check on wires to see if maybe one wire is.broken. if it is while driving it could occasionally touch together allowing it to intermittently send signal to the speedometer.