With Manufacturer's Scan Tool

Intake Manifold Change-Over Valve -N156-, Checking

The check need only be carried out when performance is poor.
The change-over from long to short intake channels occurs at approx. 4400 rpm.

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







- VAG 1551 Scan tool (or VAG 1552) with VAG 1551/3 adapter cable

NOTE: All functions which could previously be performed with VAG 1551/1552 can also be performed with the VAS 5051.







- VAG 1390 Hand vacuum pump

Checking function
- Start engine and run at idle speed.

The actuator (vacuum unit) on the intake manifold holds the change-over barrel in position for long intake channel.







- Have a second person press accelerator pedal down fully onto limit stop (throttle burst). Observe vacuum unit for Intake Manifold Change-Over Valve -N156- (location: on left of intake manifold). The actuating element must rotate the barrel in the intake manifold (arrow).
- Switch off ignition.

If the actuating element does not perform the change-over sequence:
- First check the activation of the Intake Manifold Change-Over Valve -N156- via Output Diagnosis Test Mode (DTM)
[1][2][3]Output Diagnostic Test Mode (DTM) (Function 03).

If activation is OK.:
- Connect scan tool.







- Pull vacuum hose -1-off non-return valve -2-.
- Connect hand vacuum pump VAG 1390 to non-return valve -2-.







- Perform Output Diagnosis Test Mode (DTM) again.When the Intake Manifold Change-Over Valve -N156- valve is activated, operate the hand pump uniformly.The actuating element must switch back and forth between both positions.

If the change-over does not function as described:
- Check change-over mechanics for freedom of movement. Move the rods by hand.
- Check vacuum pipes for correct connection.
- Check the vacuum system including the vacuum reservoir.

NOTE: The vacuum reservoir is bolted below the intake manifold.