The PCM uses this information to determine how much load is on the engine. Problems with this sensor can cause hesitation, fuel mixture and spark timing problems. The MAF sensor uses a heated wire or filament to measure airflow into the engine.
This is vital information for controlling the fuel mixture. The most common problem here is contamination of the sensor element with dirt or fuel varnish. A dirty MAF sensor will typically report less airflow than is actually occurring. This can cause a lean fuel condition, hesitation, and reduced performance. A sluggish or unresponsive MAF sensor can often be restored to normal operation by cleaning the sensor element with aerosol electronics cleaner.
Many engines also have a Camshaft Position CMP sensor that helps the computer figure out the correct firing order of the engine. A failure of either sensor may prevent the engine from starting or running. Two types of sensors are commonly used for these applications: magnetic sensors or Hall effect sensors. Magnetic sensors have a wire coil wrapped around a magnetic core.
When the tip of the sensor passes over a notch on a ring attached to the crank, it changes the magnetic field and produces a small current. With Hall effect sensors, a reference voltage is supplied to the sensor by the PCM to detect notches in the crank wheel. Crank sensors may be mounted on the front of the engine and read notches in the crank pulley or mounted on the block to read a notched ring on the crank itself.
The cam sensor s if used, are usually mounted in the cylinder head s and read a ring on the camshaft s. Loss of a signal or an erratic signal will usually set a fault code. The resistance of magnetic sensors can be measured with an ohmmeter. If out of range, the sensor needs to be replaced. The sensor ring also needs to be inspected for damaged, missing or cracked teeth as any of these conditions can cause erratic sensor readings.
Most late model vehicles have several magnetic speed sensors. The Vehicle Speed Sensor VSS is usually located on the transmission output shaft and provides a signal that is proportional to vehicle speed. The transmission also has one or two additional internal sensors for monitoring the relative speeds of the main input and output shafts. Faults in speed sensor circuits usually tend to be wiring related rather than outright sensor failures.
In order to do their jobs, all oxygen sensors must be exposed to a constant stream of harmful exhaust gasses, extreme heat and high velocity particulates. Because of this, their efficiency will inevitably decrease over time. Sometimes, oxygen sensors can become contaminated by elements from within the engine.
Exhaust from an overly rich fuel mixture can foul an O2 sensor, as will leaded fuel. Antifreeze or silicone residue resulting from faulty gaskets can have the same effect. The sensors pictured below have been poisoned and need to be replaced. Carbon buildup from a rich fuel mixture is a frequent occurrence and causes many sensors to go bad. There are many possible causes of this, including a clogged air filter or a leaking or defective fuel injector. Antifreeze can be very harmful to a sensor if it is allowed into the combustion chamber.
This can happen in the case of a cracked or warped cylinder head, a leaking cylinder head gasket, or a leaking intake manifold gasket. Silicone poisoning, as pictured to the left, can leave the head of an oxygen sensor appearing white in color.
The most common cause of this condition is the use of an improper silicone gasket sealant on the engine. Using improper leaded gasoline will harm an oxygen sensor. Although this is a rare occurrence, it is good to know what the effects of leaded gasoline look like on a sensor.
Soak the sensor thread area with a powerful penetrating lubricant. Starting and revving the engine should further aid in loosening the sensor by heating up the bung.
If you are using an open end wrench, try an O2 socket. If this fails, try a long ratchet or breaker bar in conjunction with your socket to generate more torque.
If you are still unsuccessful, heat the bung with a torch until cherry red and remove the sensor. After the sensor is removed, be sure to use a thread cleaner to clean up the bung threads. In some cases the threads will need to be repaired. This can be done with a thread repair kit Walker Part Do not use an impact wrench to remove an O2 sensor, as you will most likely strip the threads in the bung.
The bright orange Check Engine light in your dashboard will usually glow if you have a bad oxygen sensor. However, a Check Engine light could also be from another problem with your engine, or even a loose gas cap. You should have your vehicle checked by a professional to find out what the problem is.
Engines are less efficient when the oxygen to fuel ratio is too rich or too lean. If your vehicle has a bad oxygen sensor, it could run irregularly or sound rough when it idles. You could also notice stalling or slow acceleration. Most emissions test failures are from a bad oxygen sensor. In some cases, a bad oxygen sensor may indicate other problems, such as a failing catalytic converter, in which case the repair can get expensive.
The sensor is located on the underside of your vehicle and may be hard to reach depending on how your vehicle was built. If this sounds like too much trouble, just bring your car to one of the four Hillmuth Certified Automotive locations in Clarksville , Columbia , Glenwood or Gaithersburg.
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