If you have recently failed your state mandated emissions test you might want to know why. Sometimes the fact that you failed just isn’t enough and we here at GIC Car Clinic in San Jose, California feel you should better understand the testing procedure and how your vehicle’s emissions equipment operates. We have compiled the list below of some of the more common reasons you may have failed the emissions test.
- Dirty air filter: A dirty air filter will prevent your car from getting the proper amount of air into the engine. It can even restrict air flow to the point that your car will not run properly. You should change your air filter every 15,000 miles, more often if you live in a dusty area.
- Faulty Oxygen Sensor (O2 Sensor): The O2 sensor sends data to the car’s ECU about the oxygen content in the exhaust gases. This information can then be used to determine how much fuel the engine needs. More about oxygen sensors.
- Faulty Manifold Absolute Pressure sensor: The MAP sensor gauges the amount of vacuum the engine is creating and sends this data to the ECU allowing the computer to send the proper amount of fuel to the injection system. A bad MAP sensor will not send the right data and will cause high carbon monoxide emissions.
- Defective throttle position sensor: The TPS sends information to the ECU about the position of the throttle plate in the intake system. This sensor is very important in that it basically tells the vehicle’s computer how much or how little fuel the driver is demanding by the position of his foot on the gas pedal. If this sensor is defective, it could read completely opposite of the driver’s demands and cause high carbon monoxide emissions.
- Faulty engine coolant temperature sensor: If the ECT goes bad, it could tell the ECU that the engine is cooler than it really is and the ECU will, in turn, send more fuel to the engine. This fuel would not be needed and a rich condition would exist creating higher CO emissions.