Test Point 5 - Air Flow Sensor
TEST POINT 5a: - Air flow sensor (V/Ohms) - Fault code 1_21Possible Causes, Elimination, Remarks
The ratio between "Up" (potentiometer voltage) and "Uv" (supply voltage) can be displayed in the "Actual value" - menu with the system tester 9288.
The ratio must be approx. 0.0 to 1 when the air flow sensor plate is opened. If not:
Check Voltage supply.
Connect a voltmeter to terminal 3 and ground of the disconnected plug of the air flow sensor using test leads. Turn on ignition.
Display: 5 ± 0.3 Volt
TEST POINT 5b: - Check Voltage drop across the air flow sensor plate potentiometer. (V)
Possible Causes, Elimination, Remarks
Disconnect the air filter connecting hose. Using test leads, connect pin 3 of the disconnected air flow sensor plug with air flow sensor plug terminal 3 and pin 4 with air flow sensor plug terminal 4.
Connect a voltmeter to air flow sensor terminal 2 and ground. (turn on ignition)
Display: approx. 250 - 260 mV
Using a non-metallic tool (e.g. screwdriver handle), press the air flow sensor plate to full load position.
It must be possible to move the air flow sensor plate easily and without jamming. Observe the voltmeter's display at the same time. It must not be possible to observe voltage jumps or a voltage drop during the opening or closing operations of the air flow sensor plate.
Air flow sensor plate at full load:
Display approx. 4.60 Volts
If the voltage values are achieved, switch off the ignition and connect the plug again.
NOTE: In the event of failure of the air flow sensor, substitute values are formed by the control unit (emergency running program). In idling operation, ti signal from nominal air of the idle speed volumetric efficiency regulator. In partial and full load ranges, a constant ti signal in each case.