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Air Flow Meter/Sensor: Testing and Inspection







CHECKING THE MASS AIR FLOW SENSOR

Start the engine and let it run at idling speed. Check the CO content. If it is higher than 6% it cannot be adjusted by means of the CO adjusting screw. Switch off the engine.
1. Remove the mass air flow sensor from the air cleaner side. Check whether the hot wire (filament) is intact.
A. Hot wire (filament) defective: Change the mass air flow sensor.
B. Hot wire (filament) OK: Check the mass air flow sensor connector and wiring by:
- Unplugging the mass air flow sensor and control module connectors and removing the cover from the control module connector.
- Check that the wiring and connections are OK. If the wiring is OK, plug in the control module connector.
2. Check the hot wire (filament) burn-off function.






CHECKING THE HOT WIRE

1. Detach the mass air flow sensor from the air cleaner and check whether the hot wire (filament) is OK.
2. Start the engine and warm it up to a temperature of at least 65°C (149°F) and then let it idle. Rev the engine up to 2500 rpm, release the accelerator and let It return to idling speed again.
3. Switch off the ignition. The hot wire (filament) should glow brightly about four seconds after- wards for about a second. If nothing happens, check the wiring.
4. Start the engine and rev it up to 2500 rpm. Connect the test prods to pins 1 and 4 of the mass air flow sensor connector. Switch off the engine. Four seconds later the voltage should rise to 4 V for about one second.
5. If nothing happens, check the red/white (RD/VT) lead between pin 1 of the mass air flow sensor connector and pin 8 of the control module connector, and the black (SV) lead between pin 4 of the mass air flow sensor connector and one of the engine grounding points. If the wiring is OK, test the system using a different control module.
6. Start the engine and repeat the above test procedure. If the correct voltage is now obtained but the burn-off function does not come into operation, fit a new mass air flow sensor.

Note: The Limp-Home function takes over automatically if the hot wire (filament) breaks.






CHECKING AND ADJUSTING THE CO CONTENT

1. Connect the CO meter, exhaust extraction equipment and tachometer.
2. Start the engine and warm it up. Check the CO content, If the CO content is not to specification, turn the adjusting screw:

clockwise if it is too low

anti-clockwise if it is too high.

3. If the CO content is higher than 6% and cannot therefore be adjusted, switch off the engine. Unplug the mass air flow sensor connector and connect the multimeter across pins 3 and 6 of the mass air flow sensor.
A. Turn the adjusting screw as many turns as required to obtain a reading of 380 ohms.
B. If you cannot obtain this reading, fit a new mass air flow sensor. On obtaining the correct reading, 380 ohms, plug in the mass air flow sensor connector. Start the engine and warm it up. Check the CO content again and adjust it further until it is exactly right. If the correct CO content still cannot be obtained, check the mass air flow sensor wiring and connections
4. If the wiring is OK and the CO content still cannot be adjusted, try a new control module.

CHECKING THE BASIC SETTING OF THE FUEL INJECTION SYSTEM (CARS WITH CATALYTIC CONVERTER)

Note: There are no specified intervals at which the basic setting of the fuel injection system should be checked or adjusted.This setting establishes a reference point for the LH system and does not affect vehicle performance. Recalibration is necessary only if the performance of the engine has been disturbed by major work on it, such as replacement of the electronic control module, the NTC resistor or the mass air flow sensor, or by a major overhaul, cylinder head work or timing chain replacement.






1. Remove the plug from the potentiometer screw on the side of the mass air flow sensor.
2. Unplug the wiring harness connector from the mass air flow sensor.
3. Connect the multimeter to pins 3 and 6 as shown in the figure. The instrument should read 380 ohms. Adjust as necessary by turning the potentiometer screw. This is the first step in checking and adjusting the basic setting.
4. Plug the wiring harness into the mass air flow sensor again.
5. Connect pulse ratio meter 83 93 597 to the test point adjacent to the evaporator housing by means of the adapter lead in 83 94 132.
6. Start the engine and run it until the radiator fan cuts in.
7. If the basic setting is correct, the meter needle will swing back and forth between both ends of the scale.

Note: The movement of the needle will not be rapid and there may be a pause between each movement.

8. If adjustment is necessary, turn the potentiometer screw in the mass air flow sensor as follows:
A. If the needle remains stationary at the higher end of the scale or spends most of its time at this end, turn the screw anticlockwise until the needle stays roughly the same length of time at both ends of the scale.
B. If the needle remains stationary on the lefthand side of the scale, turn the potentiometer screw until it stays roughly the same length of time at both ends of the scale.
9. Fit the plug back in the mass air flow sensor.

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