To replace Volvo sensors, first identify the sensor that is malfunctioning. If it is the oxygen sensor, locate it behind the catalytic converter. Unscrew it from the exhaust pipe, and detach the connector. To replace the second oxygen sensor in front of the catalytic converter, repeat the same process.
Replacing Volvo sensors, particularly oxygen sensors, is sometimes a job best left to professionals. This is because of the location of the sensor that comes before the catalytic converter. It is located either on the downpipe or exhaust manifold, and unlike the easily accessible sensor behind the catalytic converter, it is often hard to reach. If you are able to replace the sensors without professional assistance, remember not to interchange them; each sensor has its own purpose and must be installed in the correct spot to function optimally.
Oxygen sensors detect the ratio of oxygen to fuel in a vehicle's exhaust. If the care is emitting too much or too little fuel, it notifies the ECU, and the vehicle adjusts accordingly. Burning too little exhaust can melt the engine's pistons and valves. Burning too much exhaust can ruin the vehicle's spark plugs and cause a failed emissions test. Sensing the level of emissions is the job of the oxygen sensor located in front of the catalytic converter.
The sensor on the back is purely dedicated to the function of the catalytic converter, and if it is malfunctioning, a check engine light may appear on the dashboard.