Automotive Technology Course | MAF or Mass Air Flow Sensor Testing

Automotive Technology Course | MAF or Mass Air Flow Sensor Testing


Oh you you you here we can see the vein airflow position sensor attached to the green there flow flap this flat for vein changes position as air enters the actual air conduit hence the name vein airflow sensor the vein airflow sensor is a mechanical device that senses the air flow through a side mounted flat position sensor as the air enters the vein air flow sensor the flap moves a specific amount this movement is registered by the side mounted flat position sensor as the flap open and closes the voltage output up the flap position sensor changes the vane type mass airflow sensor does not measure air mass in other words there is more air molecules present at lower temperatures than there are at higher temperatures for this reason this older mass airflow sensor type also incorporates an air temperature sensor within the actual unit this air temperature input is used by the ECM to fine-tune mass airflow input value the hotwire mass airflow sensor is a device that measures incoming air by the amount of current flow needed to maintain a specific temperature across a hot platinum wire element as the air enters the intake duct and cools down the hot wire element the mass airflow sensors circuitry will increase or decrease the current needed to maintain that specific temperature the change in current is then converted into a voltage signal which is then used by the ECM as a signal for air flow also remember that the voltage output signal produced by the hotwire mass airflow sensor is directly proportional to the amount of air and to ring the engine so that as their flow increases so does the voltage output of the sensor unit there are various types of mass airflow sensors using the hot wire principle in this photograph we see a mass airflow with multiple hot wire elements regardless of the type they all work the same which is by changing the current across the hot wire to maintain a specific temperature some hotwire mass airflow sensors output a frequency this frequency is amused by the ECM as a sign for airflow and to ring the engine when testing this type of mass airflow sensor always divide one by the time to complete one entire cycle this will give you the frequency of the mass airflow sensor all you have to do then is compare the frequency the proper specifications so again simply analyze one cycle produced by the mass airflow divide one by this time period and then compare the frequency value to proper specifications however most mass airflow sensors output an actual voltage signal one of the first indications that you’ll ever have of a faulty mass airflow sensor is an off scale Baro or barometric value reading the barometric reading is taken from the mass airflow sensor during wide-open throttle conditions a second indication of a faulty mass airflow sensor is the ECM not being in fuel control so always look after the barometric reading as a first indication of a mass airflow impending problem secondly make sure that the oxygen sensor is always cycling except during wide open funnel so long as the o2 sensor is cycling the ACM isn’t full control of the air fuel mixture there are only two conditions whereby the ECM is not in air fuel control these are during a wide-open throttle condition and during the deceleration period during a wide-open throttle the ECM makes sure the engine has the full amount of fuel needed for acceleration and totally disregards the oxygen sensor and during a deceleration period the ECM cuts fuel pulsation completely in this photograph we see any cm in full control of the air fuel mixture notice how the o2 sensor keeps cycling during the loaded period this example also shows the use of a graphing scanner which is extremely important during modern Diagnostics the first step in testing any mass airflow sensor problems is to analyze the barometric value on the scan tool in our test vehicle afford the barometric reading should be at around 159 Hertz at sea level always make sure to look up the proper specifications secondly also using the scanner analyze the fuel trims and the mass air flow sensor pids as a rule most mass airflow sensor problems tend to make the engine run very low since the mass airflow sensor cannot detect the actual amount of incoming airflow normally the mass airflow sensor output should be at around four grams per second but always consult proper specifications generally speaking the short term fuel trims will always stay at around zero percent and the long term fuel trims follow in closely a long term fuel trim value above or below plus or minus 10% is indicative of an open-loop air fuel mode and possibly a mass airflow sensor impending problem typical long term fuel trims during a problem with the mass airflow sensor of between 18 to 20 percent one of the first thing to do whenever testing a mass airflow sensor is to pull out wiring diagram whenever reading wiring diagrams it is always useful to highlight the three main aspects of any circuit which are the power ground and signal circuits in our test vehicle two separate grounds are used the sensor ground and the mass airflow signal ground the power feed seen here in red is used for every aspect of the mass airflow sensor operation and the signal circuit highlighted here in blue is the ECM input for air flow step number four prepare to perform all electrical tests following the wiring diagram these are the power feed patoot grounds and the signal circuits first plant the black digital multimeter lead to a suitable ground either chassis or battery ground then crimp the red digital multimeter lead to the mass airflow sensor power feet wire with the engine running full system voltage should be seen be aware of the fact that excessive ripple caused by a defective battery or alternator diode could have disastrous effects on the mass airflow sensor output signal and therefore fun engine operation any alternator or battery fault may also have a huge impact on the rest of the sensors computers and related actuator circuits then connect the red multimeter lead to the mass airflow sensor ground circuit this first round circuit is used to drive the Hotwire side of the mass airflow sensor a second separate ground is also used for the mass airflow sensor signal circuit this is done to prevent ground noise from entering the mass airflow sensor signal circuit when testing any ECM ground circuit always follow the 100 millivolts rule which says that any ECM non floating ground should not drop more than 100 milli volts between battery or chassis ground and sends her ground this 100 millivolts rule can always be used to test any computer ground circuit then proceeded to test the mass airflow sensor signal ground by tapping into its respective wire and following the same 100 millivolts rule it is always a good idea to grab the mass air flow sensor ground in order to detect any ground noise entering the mass airflow circuit since the sensor ground is a return circuit for the mass airflow sensor any problems here will have disastrous effects on the output of the mass airflow sensor corroded battery terminals defective alternators and batteries are all sources of excessive ground noise finally prepared to test the mass airflow sensor signal circuit itself connect the red lead of the multimeter to the mass airflow sensor signal wire remember throughout this test leave the digital multimeter black lead connected to battery or chassis ground the first step in testing the mass airflow sensor signal is to test at a dipole compare the space line reading to proper specifications if the mass airflow sensor is out of calibration this is the first test where you’ll ever see it then while still tapping on the mass airflow sensor signal wire boost the throttle record and freeze the waveform the frozen mass airflow sensor signal can then be used later on for analysis after freezing the waveform use the graphing multimeter or oscilloscope cursors to make the necessary measurements the first thing is to look for reference voltage during the wide open throttle condition in this vehicle it is close to 5 volts however always look for proper reference voltage specifications before testing if a faulty mass airflow sensor is detected remove it and visually inspect the hot wire element residue from oil dirt and air filter fibers are the main components of mass airflow sensor contaminants this contamination severely affects the mass airflow sensors ability to detect incoming air the end result is a lean condition caused by the inability of the mass airflow sensor to detect incoming airflow the final step in testing the mass airflow sensor is to perform a visual inspection of the air intake duct this last step is many times overlooked by technicians but it forms an integral part of mass airflow sensor testing you


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