Oxygen sensors constantly read the oxygen content of your vehicle's exhaust manifold, sending voltage signals to the engine's fuel injection computer to regulate the air-fuel mixture needed to properly power the engine. Although the upstream oxygen sensor, located in the exhaust manifold or exhaust downpipe in front of the catalytic converter, acts as the central component of the electronic fuel injection system, failure of the front or rear sensors results in the same crop of problems.
Most commonly, a failing upstream oxygen sensor leads to decreased fuel economy. Faulty sensors can also cause power loss, especially when accelerating from a stationary position. Other problems caused by upstream oxygen sensor failure include engine hesitation and surging or rapid acceleration and deceleration cycles. This issue may also cause your car to fail an emissions test.
Engines that run rich -- mix too much gas with too little air -- often cause oxygen sensor failure due to carbon buildup on the sensor's inlets. Less commonly, fumes released from silicone-based sealers such as room-temperature vulcanizing compounds damage sensors. Other causes of failure in upstream oxygen sensors include exposure to antifreeze, coolant or leaded fuel.
While decreased fuel economy and sluggish acceleration are red flags of oxygen sensor failure, there are more precision methods for diagnosing this problem. As oxygen sensors rely on electronic communication, modern vehicles equipped with an upstream oxygen sensor also have fuel injection computers. These computers feature a connection port for a diagnostic tools. When connected, the fuel injection computer feeds the tool codes that indicate operational errors, known as diagnostic trouble codes. Certain diagnostic codes indicate the failure of oxygen sensors. For instance, in OBD-II diagnostic systems, codes P0030 through P0038 and P0130 through P0147, among others, indicate faulty oxygen sensors.
Oxygen sensors, both front and rear, should be replaced every 60,000 to 100,000 miles, or as recommended by your vehicle's owner's manual. Typically, cars produced before the early 1990s require oxygen sensor replacement every 30,000 to 50,000 miles. Even if still functional, old upstream oxygen sensors can diminish fuel efficiency, cause sluggish performance and reduce the life of the carburetor.
