Video tutorial on how to to test and replace a mass airflow sensor on a BMW M62. This particular car I am working here is a 1997 BMW 540i, equipped with non-vanos, this exact engine can also be found on the BMW E31 and E38 models as well. Bosch has provided me with the parts in order to do the replacement and produce the video for everyone. This is a four wire system system which uses an electronically heated metal film to measure the amount of air passing through the intake. If this metal film becomes baked up with dirt or eventually fatigues over time, it will provide false readings to the engine which affects the air/fuel ratio. This will lead to hard starts, stumbling at idle or throughout the rpm range, poor performance, poor fuel economy, hesitations and perhaps engine stalling.


Tools/Supplies Needed:
-OBD2 scanner
-standard screwdriver
-jumper wires
-needles, staples, paper clips
-replacement Bosch mass airflow sensor
-multimeter


Procedure:
-starting with the OBD2 code reader, you will need one which is able to provide live data when the engine is running
-plug the scanner into the OBD2 diagnostic port and select the calculated LOAD value
-2.7% at idle, we should have a low value and then it’ll increase once the engine rpm is increased
-at wide open throttle, it should achieve 100%
-at 2500 rpm I had a reading of 14%
-now for taking a reading directly from the mass air flow sensor
-at idle, my reading at about 4.9 grams per second
-at 2500rpm, the reading was 24 grams per second
-keep in mind, these values are based on the brand new mass airflow sensor, not the old sensor, I haven’t been able to find BMW specific factory values
-next is testing with a multimeter, turn the ignition to the on position but not run
-this is done by selecting the 20v DC setting on your multimeter, taking the negative probe, insert it into the brown wire’s pin. Now taking the positive probe, insert that into the RED with BLUE stripe wire
-the connector should be providing current battery voltage when the ignition is on, so the reading of about 12.04V is good
-ff the reading is low or not existent, you will need to take a reading at only the RED with a blue stripe wire with a generic body ground to ensure that wire is function
-and then using the ground with a known 12V power supply in the vehicle
-for a low or non existent reading, you may have a corroded connector, faulty connector, or broken wire
-in order to back probe the connector, use a dull needle, paper clip, extremely small nail, staple or something thing to push along the side of the wire casing and weatherproof seal directly to the terminal inside the plastic connector
-we are inserting the needles in the two remaining wires which is the grey with a yellow stripe and the other is grey with a blue stripe
-using jumper wires, don’t cross the two contact, these will be connect to the multimeter
-using the same setting as before on the multimeter, the 20V DC setting
-at idle, the lowest reading was about 0.88V and as the rpm increases, so does the value. If the reading is excessively high at idle, then there is a fault with the sensor
-if the reading is lower, again there maybe a fault with the sensor, the air filter is dirty or the intake track might be pulled with debris
-I didn’t take the car to redline, but at about 3500rpm the reading is 1.99V
-if you are noticing any flat spots, not smooth linear increase, or the value won’t increase, then there is a fault with the mass airflow sensor
-at redline, the sensor should put out a full 5 volts
-for replacement, start by loosening the gear clamp on the intake tube, once loose, pull it back
-disconnect the electrical connector which will twist counter clockwise until it stops, then pull off the connection
-you can remove the air box if you wish, but it really isn’t needed
-remove the two snap clips, there is one on the bottom and then another on the top
-pull back from the air box and lift out
-once disconnected, you can remove it from the rubber intake tube
-compare the old and new sensor to ensure they are the same type and style
-BMW does use a Bosch sensor from factory on this particular car
-ensure the intake connections are clean and install the new sensor in reverse of removal