Checking control unit voltage supply — AUDI

ALZ
Note:

The engine control unit is supplied with voltage (+) at contact 3 when the ignition is switched on (voltage supply via relay). By means of this relay the engine control unit maintains the voltage supply at contact 3 for about another 25 seconds after the ignition is switched off.

In addition, contact 62 is supplied directly with voltage (terminal 15) from the central electrics unit.

The earth connection of the engine control unit is made via contacts 1 and 2.

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required

Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
Test box V.A.G 1598/31
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Current flow diagram

Check conditions

The battery voltage must be at least 11.5 V.
Fuses for engine control unit must be OK.

=> Current flow diagrams, Electrical fault finding and fitting locations binder

Alternator OK, checking:

=> Current flow diagrams, Electrical fault finding and fitting locations binder

Test sequence

Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551). Select engine electronics control unit by entering the address word "01" => Page
01-12
; when doing this the engine must be running at idling speed.
If engine does not start, carry out test with ignition switched on.

Rapid data transfer
HELP
Select function XX
Indicated on display:

Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Read measured value block
HELP
Input display group number XXX
Indicated on display:

Press keys 0, 0 and 4 for "Display group number 4" and confirm entry with Q key.

Read measured value block 4
⇒
1
2
3
4
Indicated on display:
(1...4 = Display zones)

Read off figure displayed in display zone 2.

Specification: at least 11.5 V

Press the ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
Switch off ignition.

If the specification is not attained:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
=> Page
24-26
.

Testing voltage supply for Simos control unit current supply relay (J363)

Fitting location: see Fitting locations overview =>Page
24-5
.

Switch ignition on.
Measure supply voltage using multimeter and test leads from V.A.G 1594 between sockets 1 and 3 of test box:

Specification: at least 11.5 V

If the specification is not attained:

Test wiring and earth connection to current supply relay (J363) according to current flow diagram:

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

If wiring is OK:

Replace current supply relay.

Checking voltage supply (terminal 15)

Measure supply voltage using multimeter and test leads from V.A.G 1594 between sockets 2 and 62 of test box:
Switch on ignition.

Specification: at least 11.5 V

If the specification is not attained:

Check wiring to fuse carrier and earth connection of engine control unit using current flow diagram:

=> Current flow diagrams, Electrical fault finding and Fitting locations binder