Audi Workshop Service and Repair Manuals

The Hall sensor indicates the ignition position for cylinder 1.

If the Hall sensor fails to function, the knock control is switched off and the ignition timing is retarded slightly because the signals can no longer be assigned to the cylinders.

Even without a signal from the Hall sensor, the engine will continue to run and can also be restarted.

• ◆ When a fault is detected, the engine control unit produces one spark for each cylinder on every crankshaft revolution.
• ◆ The fact that the control unit is out of phase by one engine revolution does not have any noticeable effect on the injection system. If this happens, the fuel is injected "upstream" (before the closed inlet valve) instead of while the inlet valve is open. This has only a minor influence on the quality of the air/fuel mixture.

Note on signal testing with an oscilloscope:

The centre point of the window of the Hall sensor must lie on the third falling flank of the engine speed signal after the reference mark gap.

• ‒ Push back the rubber sleeve on the Hall sensor connector.
• ‒ → Connect the V.A.G 1527 diode test lamp to contacts 1 and 2 on the Hall sensor connector from behind (the connector remains attached to the Hall sensor).

Note:

The connector contacts are numbered on the back of the connector.

• ‒ Operate the starter for a few seconds.

• The diode test lamp must flash briefly on each second engine revolution.

If the diode test lamp does not flash:

• ‒ Disconnect connector from Hall sender.
• ‒ Switch the ignition on.
• ‒ → Connect multimeter to measure voltage at contacts 1 and 3 of the connector:

• Specified result: 4.5 ... 5.5 V

• ‒ Connect multimeter to measure voltage at contacts 2 and 3 of the connector:

• Specified result: approx. battery voltage

If specified result is attained:

• ‒ Renew Hall sensor (G40).

If specified result is not attained:

• ‒ Switch off ignition.
• ‒ Connect the V.A.G 1598/22 test box to the wiring harness for the engine control unit.
  =>Page 24-6.

The following wiring connections should be checked for open circuits and/or short to positive or negative:

• ‒ Rectify short circuit or open circuit if necessary.