Mounted in the exhaust stream, oxygen sensors are important components of any late-model engine's emissions system and its computerized engine control system. 1999 Dodge Dakotas came equipped with either four-cylinder, six-cylinder or eight-cylinder engines, each of which utilized oxygen sensors. Symptoms of sensor malfunction are the same on all engine variants.
According to the AA1 Car website, an oxygen sensor on any vehicle measures the amount of unburned oxygen in the exhaust stream and tells the engine control computer whether the gasoline-and-air mixture going into the engine is too rich or too lean. When the oxygen sensor, or 02 sensor, malfunctions, the computer receives false information on how it should adjust the gas-and-air mixture and acts accordingly. If the computer thinks the engine is running the mixture too lean -- too much oxygen -- it will adjust to include more fuel in the mixture. The truck will therefore burn more gas than it needs to do a given amount of work. If you've paid attention to your Dakota's fuel economy over the years, you will likely notice a difference in the pickup's fuel economy.
In "Oxygen Sensors Are a Critical Key to Passing Emissions," Autohaus Arizona details the role an oxygen sensor plays in a vehicle's emissions performance. The gas-and-air mixture in a modern, fuel-injected car can change very quickly, requiring the oxygen sensor to send constant signals to the computer so it can make adjustments to the mixture and help the catalytic converter control hydrocarbon, carbon monoxide and nitrous oxide emissions. It does this by sending an electronic signal of varying voltage to the computer; the strength of the signal is directly related to the amount of oxygen in the gas-and-air mixture. With a failing oxygen sensor, the computer will allow too much fuel in the mixture and produce more emissions. One symptom of a failing sensor will therefore be the inability of the truck to pass emissions testing.
Control of the gas-and-air mixture is one of the most important factors in assuring that an engine runs smoothly and produces maximum horsepower and torque. Whether the 1999 Dakota in question is equipped with the four-cylinder, the six-cylinder or the eight-cylinder motor, a failing oxygen sensor will have a noticeable effect on the vehicle's idling and acceleration. The engine may hesitate, race or threaten to cut off. At stoplights, the motor may stumble and even stop. This is because the malfunctioning sensor is sending the wrong signal to the computer, causing erroneous adjustments to the gas-and-air mixture that is going into the engine cylinders.
As a malfunctioning sensor will cause improper variations in the air-and-gas mixture, when the computer allows too much gas in the mixture that's going into the cylinders, it allows too much unburned fuel in the exhaust. This can cause irreparable damage to the truck's catalytic converter, requiring an expensive repair.
