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Oxygen Sensor Testing

Madhavi Ghare
Read on to know more about the importance of testing regarding oxygen sensors. You can also gain information about performing a simple test of these devices to know of your car is working properly.


Oxygen sensors can detect the amount of oxygen in the exhaust gas being emitted from the car, and determine if the air to fuel ratio is at an optimum level (ideal value is 14.7:1)
When the amount of air in the exhaust is greater, then the mixture is said to be a lean. In this case, the exhaust fumes will be full of nitrogen oxides. Such a mixture may often cause an increase in the fuel efficiency of the car, but it may lead to an eventual damage to the engines.
When the amount of fuel in the exhaust is greater, the exhaust fumes will be full of unburnt fuel vapors that are full of hydrocarbons, and the mixture is said to be rich. This may cause an increase in the power of the car, and a decrease in the car's fuel economy. However, this can eventually lead to damage of the catalytic converter of the car.
The engine management computer or ECU checks the data supplied by the oxygen sensor against reference tables, and adjusts the air-fuel ratio in order to have complete combustion occurring in the engine.

Testing Process

Most automobile mechanics test the device to see if it is in working order.
The equipment needed is a high impedance DC voltmeter. Attach the positive lead of the voltmeter to the oxygen sensor's output wire while it is attached to the car's ECU. One can also use jumper wires to gain this access. The negative lead of the voltmeter is to be attached to the ground or on the engine block or an accessory bracket.
Set the voltmeter to look for 1 volt DC. In cold, the engine should output between 0.1 volts to 0.2 volts, when the engine has been running for over 20 minutes. It will get warm and the output should fluctuate between 0.1 volts to 0.9 volts.
Some cars use either 2 or 3 wires instead of one. In these vehicles, the heated sensors will give an output of 12 volts on one lead, ground on the second lead, and the sensor signal on the third lead. Thus, when you turn the key to 'ON' but do not start the engine, there will be a change in the signal.


Oxygen sensors perform an important function in a car: it ensures that the vehicle performs optimally. Along with this function, this device is also useful to maintain emission levels from the car's exhaust gas in order to control environmental pollution.
Normally, an oxygen sensor has a life for 30,000 to 50,000 miles in an non-heated condition, and for 100,000 miles in a heated condition.
Apart from this, other factors like soot on the ceramic element on the device, use of leaded fuels, use of fuels with silicones or silicates, etc., can lead to damage and failure of the sensors and hamper the vehicle's performance.

Symptoms of Sensor Malfunctioning

Firstly, in case of improper working, the car's fuel economy drops, and it begins to lose power. However, as a disclaimer, it would be right to state here that these symptoms do not necessarily point towards only a failure of the sensor. But, it could be one of the factors or causes, and hence needs to be checked out immediately.
Most cars also have a sensor light on the dashboard of the car. However, one should consult the owners' manual before rushing off to change the sensor when the light starts blinking. More often, the light is triggered when the car has run a certain number of miles or has been started a certain number of times.
This way, one can ensure that the oxygen sensor in one's car is in proper working order and if not, one can take the necessary steps to change, replace, or repair it.