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. However, magnetic sensors can become fouled with iron particles that stick to the tip of the sensor. Sensor inputs can be viewed on a scan tool or checked by measuring their resistance with an ohmmeter.
If the wiring is okay but the sensor is reading out of range, the sensor needs to be replaced. On vehicles where the wheel speed sensor is an integral part of the hub and wheel bearing assembly, the entire hub must be replaced if the sensor is bad. O2 Sensors are typically a low cost and quick service; but putting the issue off or ignoring it altogether can have expensive and lengthy repairs. If you ignore the signs of an O2 sensor issue, your catalytic converter is likely at risk and could potentially cause further damage to your vehicle if it quits on you.
This will vary from vehicle to vehicle, but here is a quick trick to determine how many your car has. For each exhaust pipe your vehicle has, you will have one catalytic converter a part that turns harmful gasses into less harmful gasses. For each catalytic converter, you will have two oxygen sensors. Many vehicles will have only one catalytic converter, and therefore, two oxygen sensors, but some can have four or more. The pump cell controls the oxygen concentration of the sensor by adding or subtracting oxygen to the diffusion gap.
Input to the electronic circuit modifies the oxygen concentration by changing the polarity of the current flow in the pump cell. The changing polarity of the input and trim current flow causes the control circuit to send a rich or lean signal to the engine control module. Advertisement How long should an oxygen sensor last? An oxygen sensor should outlast the vehicle emissions warranty.
Manufacturers recommend that the unheated type used from the late s to the s be inspected every 30, miles and the heated type used from the early s to the mid s be inspected every 60, miles. Manufacturers for current generation of sensors starting in the mid s should be inspected every ,00 miles.
In fact, with proper powertrain maintenance, it is possible for the sensor to last the life of the vehicle, which could be in excess of , miles. When does an oxygen sensor need to be replaced?
The service engine soon light will come on and a diagnostic trouble code s will be stored. If the sensor is damaged or not responding, it should be replaced. Advertisement There may be multiple codes stored for a sensor. A fuel delivery malfunction can be the reason for an oxygen sensor to fail. A fuel injector malfunction could be the root cause for the sensor failure.
Just replacing the sensor may not be a long-term solution. Do oxygen sensors degrade over a period of time? Simple answer: Yes. What causes an oxygen sensor to degrade? When silicon was an ingredient in RTV and coolant, the silicon could cause the sensor to rapidly degrade. It was referred to as silicon poisoning. Gasoline and diesel fuel are refined products from crude oil. The refined product contains a mixture of different hydrocarbons including Olefins, Benzene and the chemical element Sulfur.
Sulfur is a chemical element that occurs naturally in crude oil. The refining process reduces the concentration of sulfur in the gasoline. Sulfur can cause the degradation of an Oxygen sensor and the concentration of the Sulfur in the gasoline will determine the rate at which the sensor will degrade. If a high-mileage engine is using oil due to piston ring, cylinder or valve guide wear, phosphorus from the oil will contaminate the O2 sensors and accelerate the aging process.
The same applies to coolant that may be seeping past a leaky head gasket. As a rule, the service life of oxygen sensors in most and newer vehicles with OBD II should be , to , miles or more — assuming no problems that could cause the O2 sensors to fail prematurely.
On pre vintage vehicles, the oxygen sensors were not as robust, and typically had a service life of 50, to 80, miles. Because of this, some of these older vehicles did have a recommended replacement interval for changing the O2 sensors. Check The Part! Education: Selling Shocks And Struts. Magazine Current Issue Past Issues.
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