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Control Unit Inputs

The circuit information in Table u on the following page is used to make measurements at the Digifant I control unit connector, to check the components and the wiring harness which supply input signals to the control unit.

As a general rule, a complete absence of the voltage or continuity specified in the table suggests an open circuit in the wiring harness. For more specific information, see CURRENT FLOW DIAGRAMS.

Test results which differ from the value specified in the table, especially for values less than 10 ohms, do not necessarily indicate a faulty component. Check for loose connections or connections which are inadequate due to contamination or corrosion.

Use care to avoid damaging the delicate connector terminals with meter probes during testing. For safety, fabricate a set of test leads. See Fig. 8-4. Use the flat connectors (Volkswagen part no. N 17 457 2 or equivalent) to make contact with female connector terminals, then connect the meter leads to the insulated alligator clips.

Fig. 8-4. Jumper wires made with flat connectors and alligator clips, used to make contact at harness connector without damaging terminals.

CAUTION-

Floating ground connections will damage the control unit. Check for good clean system ground connections, especially at the engine, transmission, body, and the battery negative (-) terminal.

CAUTION-


Use only a high input impedance voltmeter, ohmmeter, or multimeter. The electrical characteristics of other types of test equipment may cause inaccurate results or damage to the electronic components. For more information, see FUNDAMENTALS.


Volkswagen specifies that the first step in any Digifant I system troubleshooting must be to check the OBD fault memory, and to find and correct any faults that may be indicated.

To perform these tests, turn the ignition off and disconnect the 38-pin connector from the Digifant control unit. The Digifant control unit is mounted in the upper left (driver's) side of the engine compartment, beneath the drip tray. Carefully remove the drip tray for access. Remove the control unit from its mounting bracket to disconnect the control unit connector. The connector terminals for meter connections are identified in Fig. 8-5.

Fig. 8-5. Terminal pin identification for 38-pin Digifant I control unit connector. Use care to not damage connector terminals with test probes.

CAUTION-


Always change meter ranges before making test connections.


Connect or disconnect component connectors and meter probes with the ignition off, to avoid damage to electronic components.

When performing the tests, the following conditions apply:

CAUTION-


battery voltage is within specification (see ELECTRICAL SYSTEM)


fuses 16, 18 and 21 are OK


the fuel pump and fuel pump relay are operating correctly (see 4.3 Fuel Pump)

NOTE-

specified values are valid within an ambient temperature range of 32 to 104°F (0 to 40°C).

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