Checking switchover of intake manifold flap: VW 2.8 TDI (AUH)

Special tools, workshop equipment, test and measuring equipment and accessories required

V.A.G 1390 Hand vacuum pump
Testing box V.A.G 1598/30
Hand-held multimeter V.A.G 1526 or Multimeter V.A.G 1715
Measuring aids set V.A.G 1594
Current flow diagram

Checking function

Start engine and run at idle.
Switch the ignition off.
Watch adjusting lever on intake manifold flap (2nd person required).
Intake manifold flap must close after ignition is switched off and then open again after approx. 3 seconds.

If the switchover does not take place, the following checks must be carried out.

Check the switchover mechanism of the intake manifold flap for smooth movement. To do this, actuate the linkage by hand.
Check function of vacuum control element with hand vacuum pump V.A.G 1390.
Check vacuum lines for proper connection.

If no fault is found in the mechanical components:

Check switchover valve for intake manifold flap.

Testing Procedure

Remove the connector from the intake manifold flap change-over valve =>Installation Point Overview, page
23-5
.
Measure resistance between contacts of switchover valve:
Setpoint value: 25...45 ω

If the setpoint value is not reached:

Renew switchover valve for intake manifold flap.

If the setpoint value is reached:

Set multimeter to voltage measurement and connect to contacts 1 + 2 on disconnected plug of switchover valve for intake manifold flap.
Start engine and run at idle.

Setpoint value: Battery voltage

Switch the ignition off.
Voltage value must drop to 0 V after approx. 3 seconds.

If the voltage value does not change as described:

Connect the testing box V.A.G 1598/30 to the control unit wiring loom. The engine control unit is not connected in the process.

Check for breaks in the cables between the testing box and the connector in accordance with the current flow diagram.
Contact 2+socket 2/01
Cable resistance: max. 1.5 ω
Check the wire to contact 1using the current flow diagram.
Also check the cables for short-circuit among themselves, to the vehicle earth or the battery positive terminal.
Setpoint value: ∞ω

If not fault in the cables is discovered:

Replace the control unit for diesel direct injection system (J248) =>page
23-61
.