If this system does not function, the cause may be a malfunction of the engine control unit and, above all, the mechanical camshaft adjuster. However, the "culprit" may also be the corresponding electromagnetic valve, so this valve must be checked.
Checking the camshaft control solenoid valve
1. If the valve does not activate (for example, during testing via a one-minute connection to the VAS 5051 diagnostic, measuring and information system or the VAG 1551 defectoscope), which manifests itself as the absence of a click, then in this case you need to check the internal resistance of the valve.
2. To do this, turn off the ignition. Remove the connector (arrow) from the camshaft adjuster.
Connector on the camshaft adjuster
3. To measure the valve resistance, connect a multimeter to it. The measurement is made between two contacts that are located next to each other. The nominal value is from 10 to 18 Ohms.
Measuring the resistance between the valve contacts
4. If the nominal value is provided, it is necessary to check the power supply. This assumes that fuse A on the quadruple relay panel in the electronics unit, which is located in the battery compartment, and also the fuel pump relay J17 are in good condition. To do this, it is necessary to check the fuse, the relay and the power supply to the relay.
5. If the fuse and relay are OK, connect a voltage indicator (VAG 1527 B) between the engine body and contact 1 (plus) of the previously removed camshaft adjuster plug connection.
Camshaft adjuster connector
6. Briefly operate the starter. The indicator LED should light. If the LED does not light, it is necessary to check for a break in the connection: connector contact 1 - fuse - fuel pump relay. If there is a break, fix it. If after fixing the break the LED lights up, it is necessary to check the power supply,
7. To do this, connect the voltage indicator between connector contacts 1 and 2. Apply voltage to the camshaft adjustment valve (best with the VAS 5051 diagnostic system). The LED should blink.
8. If the LED does not blink or is constantly on, you need to check for an open or short circuit to the body of the connection from contact 2 (for example, using the VAG 1598/31 control device). The LED should flash. If the wiring is OK, the engine control unit must be replaced. If the fault is not found, the mechanical camshaft adjuster must be replaced.
[The article was copied from the website «audimanual»]