Checking the air flow meter and intake air temperature sensor (VW Passat B4)

Move the protective cover of the air flow meter connector to access the wires. Without disconnecting the connector, connect a voltmeter to terminals "2" and "3" (Fig. 3-54). Set the instrument and starter switch key to the "On" position. The voltage on the voltmeter should be about 5 V. If the voltage does not correspond to this, replace the ECU. Connect the voltmeter to terminals "2" and "4" of the connector. Start the engine at idle. The voltage on the voltmeter should be within 0.5-1.5 V. On an unheated diesel engine, the voltage value may be slightly higher. Increase the crankshaft speed. The voltage on the voltmeter should smoothly increase and reach a value of about 4.5 V at maximum crankshaft speed



If the voltage increase is not smooth or the voltage does not reach the specified value, replace the air flow meter. Disconnect the air flow meter connector. Connect an ohmmeter to terminals "1" and "4" of the meter block and check that its readings correspond to the values specified above.

If the ohmmeter readings are not within the specified limits, replace the air flow meter.

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