VW Passat & Audi A4 1990-2000

Airflow Meter/sensor & MAF sensor

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OPERATION
Passat 1990-93 2.0L


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Fig. Airflow sensor Cutaway

The Airflow sensor is upstream of the throttle valve so that it measures all the air that enters the engine. It consists of an air funnel in which the air sensor plate lever is free to pivot. The airflowing through the funnel deflects the sensor plate by a given amount out of its zero position; this movement is transmitted by the sensor plate lever to the control plunger which determines the basic injection quantity required for the basic functions. The airflow sensor plate potentiometer, which is located on the airflow sensor housing, provides the CIS-E Motronic control unit with information concerning engine load. The potentiometer consists of a wiper brush working on a carbon film. The ECU provides the airflow sensor plate potentiometer with a 5-volt reference signal. As airflow increases the sensor plate provides a modified voltage signal back to the ECU via the potentiometer wiper. This input to the ECU is used to control ignition timing, acceleration, and full-throttle enrichment.

1993-2000 2.8L V-6

The mass airflow sensor provides the ECM with continuous information regarding the amount of air, or "air mass" entering the intake manifold. A "hot wire" is heated to a temperature of 180°C (356°F) above the ambient temperature. As airflows through the sensor, the current through the wire increases to maintain the 180°C (356°F) temperature. The Engine Control Module (ECM) uses this change in current as a means to determine the air mass entering the engine. The current is sensed by reading the voltage drop across the measuring resistor in the sensor. Changes in intake air temperature are corrected by the compensating resistor. The hot wire is mounted in an inner sleeve for protection. Each end of the mass airflow sensor also has a protective screen attached to help prevent damage to the wire. To clean the heated wire of contamination, it is heated to 1,000°C (1,800°F) for approximately one second when the engine is switched off.

TESTING & ADJUSTMENTS
Passat 1990-93 2.0L L4
AIRFLOW SENSOR, CHECKING & ADJUSTING
  1. Pull the injectors out of their inserts and place them in the openings of the VAG 1348/2B fuel analyzer.
  2.  
  3. Operate either the starter or a remote control (VAG 1348/3A) for approximately 10 seconds.
  4.  
  5. Check the quality of the sensor plate lever movement by lifting the sensor plate bolt using a magnet.
  6.  



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Fig. Checking sensor plate movement

  1. The sensor plate lever must exhibit the same resistance over its entire travel.
  2.  
  3. Pull the sensor plate upward with a quick movement, using a magnet on the sensor plate bolt.
  4.  
  5. No change in lever resistance should be felt.
  6.  
  7. If there is resistance or binding, replace the airflow sensor assembly.
  8.  
  9. If the sensor plate lever is difficult to move upward, but moves downward easily, replace the fuel distributor, as the control plunger is hanging up.
  10.  

CENTERING AIRFLOW SENSOR PLATE


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Fig. Centering the airflow sensor plate

  1. If the airflow sensor plate binds in the air cone, remove the bolt in the center of the sensor plate.
  2.  
  3. Apply thread-locking compound to the bolt and reinstall it, centering the sensor plate before tightening the bolt.
  4.  



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Fig. Indicating the airflow sensor plate clamping bolt

  1. If the plate cannot be centered, separate the airflow sensor housing from the air cleaner housing by releasing the wire clamps.
  2.  
  3. Remove the clamp bolt from the end of the airflow sensor lever. Coat the bolt threads with thread-locking compound and reinstall the bolt hand-tight.
  4.  
  5. Center the airflow sensor lever on the shaft and tighten the clamping bolt. Reinstall and center the airflow sensor plate, as described above.
  6.  

CHECKING SENSOR PLATE REST POSITION


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Fig. Showing the sensor plate rest position

  1. Check the airflow sensor plate rest position with the engine at normal operating temperature. When correctly adjusted, the sensor plate should be 1.9mm-3.0mm below the narrowest point of the air cone.
  2.  

ADJUSTING SENSOR PLATE REST POSITION
  1. Remove the upper section of air filter housing and remove air filter element
  2.  



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Fig. Indicating the airflow sensor plate adjusting nut

  1. Adjust the rest position using the adjustment nut under the airflow sensor plate (arrow).
  2.  


CAUTION
Do NOT bend leaf spring while performing adjustment.

CHECKING SENSOR PLATE FREE PLAY

NOTE
Prior to checking or adjusting the sensor plate free play, the sensor plate rest position must be OK and the CO adjustment must be OK



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Fig. Checking the sensor plate free play


NOTE
Free play is the clearance between the control plunger and sensor plate lever (right arrow), measured on the side of the sensor plate closest to the fuel distributor (left arrow).

  1. Crank the engine over, or use a remote control (VAG 1348/3A) for approximately 10 seconds.
  2.  
  3. Lift the sensor plate slightly until resistance is felt. Free play should be 0.5mm-3.0mm (up to edge of venturi).
  4.  
  5. If necessary, adjust the free play at the control plunger on the fuel distributor.
  6.  

ADJUSTING SENSOR PLATE FREE PLAY AT FUEL DISTRIBUTOR


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Fig. Showing the fuel distributor

  1. Adjust the sensor plate free play using wrench VW 674/2 on control plunger stop screw.
  2.  
  3. Distance "a" = 0.6 mm between stop screw and collar of hex hut.
  4.  
  5. 1/4 turn is approximately 1.3 mm of play at sensor plate.
  6.  
  7. Turning in increases free play.
  8.  
  9. Turning out decreases free play.
  10.  

Passat 1.9L Turbo Diesel
CHECKING EGR & MAF SENSOR FUNCTION

NOTE
The Mass Airflow (MAF) sensor signal is required for the ECM to calculate the optimum amount of fuel to inject and the degree of EGR control to administer. The smaller the MAF sensor signal, the smaller the quantity of fuel injected.

  1. Connect a proper scan tool.
  2.  
  3. Start the engine and let it idle.
  4.  
  5. Press "0" and "1" buttons to select Address Word 01 "Engine Electronics."
  6.  


NOTE
Secure the scan tool to the rear seat and operate it from this position, using a second technician.



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Fig. The display will appear as shown

  1. Press "0" and "8" buttons to select Function 08 "Read measuring value block."
  2.  
  3. Press the "Q" button to enter input.
  4.  



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Fig. The display will now appear as shown

  1. Press "0", "1" and "0" buttons to select "Display group 10"
  2.  
  3. Press the "Q" button to enter input .
  4.  
  5. Observe display in display zone "1".
  6.  
  7. Specification should be: 240 to 340 mg/H
  8.  



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Fig. The display, with the "Q" button pressed, will appear as shown

  1. If the indicated specification is not obtained, check the operation of the EGR valve and system.
  2.  
  3. If the proper specification is obtained, accelerate vehicle in 3rd gear from about 1,500 rpm under wide-open throttle.
  4.  
  5. Press the "PRINT" button on the scan tool (VAG 1551) when the vehicle reaches approximately 3,000 rpm.
  6.  

Specified value in display field 4: 100 %



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Fig. With WOT, the display will appear as shown

  1. If the indicated specification is not obtained, repeat the test and again accelerate the vehicle under WOT.
  2.  
  3. The specified value in the display field should be 1,800 mg/H minimum (intake air mass).
  4.  
  5. If specification is still not obtained, replace the Mass Airflow sensor.
  6.  
  7. Use the scan tool to display the Readiness code.
  8.  
  9. If DTC memory has been erased, create Readiness code.
  10.  
  11. If display field "1" shows constant 550 mg/H (firm replacement value), press the "0" and "6" buttons to select Function 06 -"End Transfer."
  12.  
  13. Press the "Q" button to enter input.
  14.  
  15. Switch the ignition to "OFF".
  16.  
  17. Disconnect the MAF sensor harness connector.
  18.  
  19. Switch the ignition to "ON".
  20.  
  21. Measure the MAF sensor voltage supply between the connector terminals shown in the MAF terminals and voltage chart illustrations.
  22.  



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Fig. Indicating the MAF terminals for voltage checking



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Fig. This voltage chart gives the proper voltage readings

  1. If the proper voltage specifications are not obtained, switch "OFF" the ignition.
  2.  
  3. Connect a VAG 1598/22 Test Box to the ECM wiring harness.
  4.  
  5. Check the wiring for open circuit between the Test Box and the harness connector, using a wiring diagram. Check between the following points:
  6.  
  7. Terminal 2 and sockets 2 and 28
  8.  
  9. Terminal 3 and socket 4
  10.  
  11. Terminal 4 and socket 50
  12.  
  13. Terminal 5 and socket 52
  14.  
  15. Wire resistance at each check point should be 1.5 ohms maximum.
  16.  
  17. Check the wires for shorts to one another or to vehicle ground and battery (B+).
  18.  
  19. At each check, the meter should indicate infinite ohms.
  20.  
  21. If the wiring is OK, replace the Diesel Direct Injection system ECM J248.
  22.  



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Fig. Identifying the terminals of the ECM harness connector for testing

Passat 1990-93 2.0L L4
AIRFLOW SENSOR LEVEL BASIC ADJUSTMENT


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Fig. Airflow sensor plate basic adjustment

  1. To check the airflow sensor level basic adjustment, measure the distance from the fuel distributor mounting surface to the sensor plate roller when the sensor plate is at rest.
  2.  
  3. The height should be 18.8mm + or - 0.1mm.
  4.  
  5. If the height is incorrect remove the tamper proof plug in the top of the airflow sensor housing and turn the idle mixture adjusting screw, using a 3 mm hex wrench, until the measurement is correct.
  6.  


NOTE
This basic adjustment is only a starting point. The adjustment is likely to change during the final step of checking and adjusting the idle mixture. If any adjustments or repairs are made to the fuel distributor or airflow sensor plate level, the idle mixture and idle speed must be checked.

ADJUSTING AIRFLOW SENSOR POTENTIOMETER


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Fig. Showing the potentiometer location

  1. With the ignition "OFF" detach the airflow sensor potentiometer harness connector.
  2.  



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Fig. Indicating the airflow sensor plate test connection

  1. Install test harness VAG 1501 (or equivalent) to the potentiometer electrical plug.
  2.  
  3. Reconnect the injection harness to the test harness.
  4.  
  5. With a Digital Multimeter (DMM) connected between terminal 1 and 3 of the test harness switch the ignition "ON".
  6.  
  7. The correct measurement should be 4.35 to 5.35 VDC.
  8.  
  9. With the ignition "OFF", connect the Digital Multimeter (DMM) between terminals 2 and 3 of the test harness.
  10.  
  11. If the voltage is below specifications, check the system for air leaks.
  12.  
  13. If the voltage exceeds specifications, adjust using the trim screw.
  14.  



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Fig. Potentiometer trim screw location

  1. Remove the sealing compound at the potentiometer trim screw.
  2.  
  3. Start the engine and run at idle for approximately 2 minutes.
  4.  


NOTE
The engine must be at normal operating temperature and the radiator cooling fan must not be running during this adjustment.



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Fig. Potentiometer voltage chart

  1. Rotate the trim screw as necessary to obtain a voltage reading that falls within the voltage graph parameters.
  2.  
  3. Seal the trim screw with an appropriate compound.
  4.  

If the potentiometer cannot be adjusted with the trim screw to obtained the correct specification, the airflow sensor assembly (complete) should be replaced.

1994-2000 1.8L, 2.7L, 2.8L
MASS AIRFLOW SENSOR CHECKING

NOTE
For this check, all electrical accessories should be switched off (coolant fan must not run during test). Ensure the fuse for the MAF sensor is OK.

  1. Connect a VAG 1551 or VAG 1552 scan tool and press buttons "0" and "1" to insert "Engine Electronics" address word 01 (with engine running at idle).
  2.  
  3. Press buttons "0" and "8" to select "Read Measuring Value Block" function 08 , and press "Q" button to confirm input.
  4.  
  5. Press buttons "0", "0" and "2" to input display group number 2 , and press the "Q" button to confirm input.
  6.  
  7. Compare the display with the specified values for engine load.
  8.  



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Fig. Showing the MAF sensor connector

  1. Disconnect the 3-pin harness connector from the MAF sensor.
  2.  
  3. Connect a DMM between harness connector terminal 3 and engine ground, using adapter cables from VW1594 connector test kit.
  4.  
  5. Switch the ignition to "ON" and measure the voltage. It should be 11.5 volts.
  6.  
  7. Switch ignition to "OFF".
  8.  

If the voltage specification is not attained, check the wiring from terminal 3 to fuse panel, using an applicable wiring diagram.

  1. Connect a VAG1598/22 test box to the ECM harness connector.
  2.  
  3. Check wiring for open circuits between the ECM/test box and the 3-pin MAF sensor harness connector. Check at the following points:
  4.  
  5. Connector terminal 1 to ECM test box socket 13
  6.  
  7. Connector terminal 2 to ECM test box socket 12
  8.  

The value should be a maximum resistance of 1.5 ohms at each test point.

  1. If not, check the wiring for short circuits between terminals of 3-pin connector. The DMM should show infinite ohms.
  2.  
  3. If the voltage supply and wiring are OK, replace the Mass Airflow (MAF) sensor-G70.
  4.  

Audi A4 1.8L


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Fig. Showing the MAF sensor 4-pin connector on the A4 with 1.8L engine

  1. Disconnect the 4-pin harness connector from Mass Airflow sensor (MAF).
  2.  
  3. Connect a DMM between harness connector terminals 1 and 3 , using the adapter cables from VW 1594 connector test kit. The specified value should be 9.0-14.5 volts.
  4.  

If there is no voltage, switch ignition the to "OFF" and check the wiring, using an applicable wiring diagram.

  1. Connect a VAG 1598/22 test box to the ECM harness connector.
  2.  
  3. Check the wiring for open circuits between the ECM/test box and the 4-pin MAF sensor harness connector at the following points:
  4.  
  5. Connector terminal 2 to ECM test box socket 12
  6.  
  7. Connector terminal 4 to ECM test box socket 13
  8.  

The preferred value at each point should be a maximum resistance of 1.5 ohms.

  1. Check wiring for short circuits between terminals of 4-pin connector, and between the connector and the ECM/test box.
  2.  
  3. Between connector terminal 4 and the ECM/test box socket 12 , the specified value should be infinite ohms.
  4.  
  5. Switch the DMM to the "20 VDC" measuring range.
  6.  
  7. Check the wiring at the 4-pin connector for short circuit to B+ (battery positive voltage), according to applicable wiring diagram.
  8.  
  9. Between the following points, the voltage should be "0" volts:
  10.  
  11. Connector terminal 2 to vehicle Ground
  12.  
  13. Connector terminal 4 to vehicle Ground
  14.  

If the wiring is OK, replace the Mass Airflow sensor (MAF)-G70.

Audi A4 2.7L


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Fig. Showing the MAF sensor connector on the A4 with 2.7L engine

  1. Disconnect the harness connector from the MAF sensor.
  2.  
  3. Connect a DMM, set in the "voltage measurement range", between socket 2 and socket 3 of the connector.
  4.  


NOTE
Socket 3 on the connector is the Ground (GND) connection from the engine control module.

  1. Operate the starter briefly. Battery voltage should be shown on the DMM.
  2.  


NOTE
The MAF sensor receives its voltage supply via the fuel pump relay.

  1. If the reading does not match the battery voltage, check for an open circuit or short to ground in the wiring circuit between the fuel pump relay and socket 2 on the connector via the fuse. Repair if necessary.
  2.  
  3. Connect a DMM, on the "voltage measurement range", between sockets 3 and 4 of the connector.
  4.  
  5. Switch ignition to "ON". The DMM should show approximately 5 volts.
  6.  

If the specification is not attained, check wiring.


NOTE
The wiring test includes also testing the signal wire.

  1. Connect a VAG1598/31 test box to the wiring harness for the ECM. Do NOT connect directly to the ECM.
  2.  
  3. Check for an open circuit and short to B+ or Ground (GND) in the wiring connections as shown in the illustration.
  4.  

The maximum wiring resistance should be 1.5 ohms.

  1. Repair any short circuit or open circuit, if necessary.
  2.  
  3. If the wiring and voltage supply are OK, replace the Mass Airflow (MAF) sensor-G70.
  4.  



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Fig. Showing terminal to socket connections

Audi A4 2.8L


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Fig. This is the 3-pin MAF sensor connector on the A4 2.8L

  1. Disconnect the 3-pin harness connector from Mass Airflow sensor (MAF).
  2.  
  3. Connect a DMM between the harness connector terminals 2 (ground) and 3 (B+), using the adapter cables from VW1594 connector test kit. The DMM should show 9.0-14.5 volts.
  4.  

If there is no voltage, switch the ignition to "OFF" and check the circuit wiring using an applicable wiring diagram.

  1. Connect a VAG1598/22 test box to ECM harness connector .
  2.  
  3. Check the wiring for open circuits between the ECM/test box and the 3-pin MAF sensor harness connector. Check between the following points:
  4.  
  5. Connector terminal 1 to ECM/test box socket 13
  6.  
  7. Connector terminal 2 to ECM/test box socket 12
  8.  

Specified value-maximum resistance 1.5 ohms.

  1. Check the wiring for short circuits between terminals of 3-pin connector, and between connector and ECM/test box.
  2.  
  3. Check between connector terminal 1 and the ECM/test box socket 12 . The specified value should be infinite ohms.
  4.  
  5. Now, switch the DMM to the "20 VDC" measuring range.
  6.  
  7. Check the wiring at the 3-pin connector for short circuit to B+ (battery positive voltage), according to applicable wiring diagram. Test at the following points:
  8.  
  9. Connector terminal 1 to vehicle ground
  10.  
  11. Connector terminal 2 to vehicle ground
  12.  

The preferred value should be "0" volts.

If the wiring is OK, replace the Mass Airflow sensor (MAF)-G70.

REMOVAL & INSTALLATION
Passat 1990-93 2.0L L4
THROTTLE SENSOR PLATE
  1. Mark position of stop screw by scribing.
  2.  
  3. Measure and record distance "a" between stop screw and hex nut collar.
  4.  
  5. Remove stop screw, using VW 674/2 wrench.
  6.  

To install:

  1. Wash control plunger with clean gasoline before installing.
  2.  
  3. Inspect stop screw sealing ring for damage, replace if necessary.
  4.  
  5. Install with smaller diameter "0" of sealing ring towards control plunger.
  6.  
  7. Insert the stop screw, using a VW 674/2 wrench, until the previously recorded dimension "a " is obtained.
  8.  
  9. Check the sensor plate rest position and free play; adjust if necessary.
  10.  


NOTE
Mechanically cleaning the control plunger is not permitted. If the piston shows heavy scoring and/or does not move easily after washing with clean gasoline, the complete fuel distributor must be replaced.

MASS AIRFLOW SENSOR
  1. Remove the intake air boot from the airflow sensor.
  2.  
  3. Remove bolts holding the fuel pressure regulator mounting bracket to the airflow sensor.
  4.  
  5. Remove the 2 small mounting screws from the top of the fuel distributor.
  6.  
  7. Remove the fuel distributor and distributor base O-ring from airflow sensor.
  8.  
  9. Separate upper and lower air cleaner housing halves.
  10.  
  11. Remove airflow sensor mounting bolts and remove the airflow sensor from upper air cleaner housing.
  12.  
  13. Installation is the reverse of removal.
  14.  


NOTE
The Airflow sensor has several basic adjustments that must be made before final assembly. These adjustments are only a starting point and some adjustment procedures will be repeated before the proper setting is achieved. Whenever such adjustments are made, the final step is to check and adjust idle speed and mixture.

All except Passat 2.0L
MASS AIRFLOW SENSOR
  1. Turn the ignition switch to the OFF position.
  2.  
  3. Disconnect the Intake Air Temperature sensor harness electrical connector.
  4.  
  5. Using a suitable tool, remove Intake Air Temperature sensor.
  6.  
  7. Installation is in reverse order of removal.
  8.  

 
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