O2 Sensor Symptoms
Learning how to test anoxygen sensorwill help you detect a potential problem with the unit in your vehicle. Oxygen sensors detect the amount of oxygen content in the exhaust system and turn this information into a voltage signal to help the computer keep emissions under control. However, whenever a sensor’s signal goes beyond its normal parameters, the vehicle’s computer stores a trouble code in its memory and turns a malfunction indicator light (MIL) or Check Engine light to alert the driver of the problem. Before blaming your car’s oxygen sensor for the malfunction, though, use the sensor’s operating characteristics to verify whether you need to replace it or another component is creating a problem in engine performance.Preparing to test the oxygen sensorTo run this test, you will need a 10-megaohmdigital voltmeter. Most digital voltmeters come with this type of protection to prevent the meter from drawing too much electrical current and damaging electrical and electronic components under test. Once you have the appropriate voltmeter on hand, warm up your car engine to operating temperature. You can do this by taking your car for a 20-minute drive on the highway or idling the engine for about 15 to 20 minutes at a fast idle speed.Turn off the engine and set your voltmeter to the mV (millivolt) scale. Connect the meter’s red wire to the oxygen sensor electrical wire and the meter’s black wire to a good ground on your engine. If your vehicle uses a heated oxygen sensor, make sure you are connected to the signal wire on the sensor. You can verify this by checking the wire connections in your vehicle service manual. If you don't have this manual on hand, you can consult one by going to the reference section of your local public library.Reading the oxygen sensor’s signalsBeforetesting the sensor, start the engine and see the sensor’s voltage signals on your voltmeter. The voltage should be cycling or fluctuating from 100 mV to 900 mV (0.10 to 0.90V) approximately. Otherwise, the oxygen sensor is not operating properly.Now, you need to see if your sensor reacts properly to changes in oxygen content in the exhaust system. First, disconnect thepositive crankcase ventilation(PCV) hose leading to the intake manifold. This will allow more air to enter the engine. Read the sensor’s signal in your voltmeter. An oxygen sensor interprets an increase in oxygen as a lean condition and emits a signal close to 2mV (0.20 V). Replace the hose to the PCV valve.Disconnect one of the plastic ducts from the air cleaner assembly on your vehicle. Block the duct opening leading to the engine with a clean rag. This will reduce the amount of air going into the engine. Read the sensor’s signal in your voltmeter. An oxygen sensor interprets a decrease in oxygen as a rich fuel condition and emits a signal close to 8mV (0.80 V). Reconnect the air duct to the air cleaner assembly and turn off the engine.If the oxygen sensor in your vehicle responded correctly to your tests, you might have a problem with another component that is affecting your oxygen sensor reading. This could be an air leak around the engine, a problem in the ignition system or something similar. If your sensor didn’t respond properly to your tests, the sensor is bad and you need to replace it.
