Digifant I

Testing Hall Sender and Coil Power Stage (Digifant I)
The Hall sender and coil power stage should be tested if there is no spark at the spark plugs when tested. These tests also check the Digifant control unit response to the Hall sender signal. For these tests, the spark plug wires and ignition coil should be in good condition. See Testing Coil and Spark Plug Wires. The Hall sender connector is on the side of the distributor. The coil power stage is located atop the coil.

These tests require the use of a high-impedance voltmeter or low-current LED test light. For more information, see Basic Troubleshooting Principles. The sequence of the tests below is important. Follow the test sequence as it is presented in order to logically isolate the faulty component.

CAUTION: Always turn the ignition OFF before connecting or disconnecting ignition test equipment. Switch multimeter functions or measurement ranges only with the test probes disconnected.

Power Stage Voltage Supply and Ground
With the ignition OFF, disconnect the power stage harness connector. Connect a voltmeter to terminals 1 and 3 as shown Fig. 3-17. When the ignition is turned ON, there should be approximately battery voltage. Turn OFF the ignition. If there is no voltage, either there is a break in the wiring from terminal 1 to the fuse relay panel, or from terminal 3 to ground. Use the wiring diagrams to check for continuity and repair any wiring breaks as necessary. Reconnect connector.

Fig. 3-17:

Fig. 3-17. Terminals identification of coil power stage connector for testing voltage and ground. Test between terminals 1 and 3.

Hall Sender Voltage Supply and Ground
With the ignition OFF, disconnect the Hall sender harness connector and the fuel injector harness connector. Using a voltmeter, check for voltage between the outer terminals of the Hall sender connector as shown in Fig. 3-12 above. When the ignition is turned ON, there should be a minimum of 10 Volts. Turn OFF the ignition. If there is no voltage, check for continuity in the wiring between terminal 3 of the Hall sender connector and terminal 30 of the Digifant control unit connector, and between terminal 1 of the Hall sender connector and ground. Repair any breaks as necessary. If the wiring is OK, then the control unit is most likely faulty. Reconnect the Hall sender harness connector.

Hall Sender Switching Function
Peel back the protective rubber boot on the Hall sender harness connector and connect an LED test light between the center terminal and either of the outer terminals. See Fig. 3-18. When the starter is actuated, the LED should flicker. If there is no reaction, the Hall sender is defective and should be replaced as described in Disassembling and Assembling Distributor.

Fig. 3-18:

Fig. 3-18. Hall sending unit switching function being tested using LED test light. Volkswagen special tools shown.

Control Unit Response to Hall Sender Signal
Remove the wiring connector from the power stage and connect an LED test light between terminals 2 and 3 of the connector. See Fig. 3-17 above. With the Hall sender wiring connector connected and fuel injector connector still disconnected, actuate the starter. The test light should flicker. If it doesn't, then either the wiring between terminal 2 of the power stage connector and terminal 11 of the control unit connector is faulty, or the control unit is faulty.

Power Stage Response to Control Unit Signal
Reconnect the power stage connector and the fuel injector connector. Connect a multimeter between terminals 1 and 15 of the coil. See Fig. 3-1 above. When the ignition is turned ON there must be 2 volts minimum, which then drops to 0 volts after 1 to 2 seconds. If not, then the coil power stage is faulty.