Camshaft Position Sensor: Testing and Inspection

Camshaft Position (CMP) Sensor -G40-, Checking







Special tools and workshop equipment required

- V.A.G 1526 A.
- V.A.G 1527 B.
- V.A.G 1594 A.
- V.A.G 1598/31.

The Camshaft Position (CMP) sensor -G40-indicates the ignition position for cylinder 1.

If the Camshaft Position (CMP) sensor -G40-fails to function, the knock recognition control is switched off and the ignition timing is retarded slightly because the signals can no longer be assigned to the cylinders. Furthermore, the charge pressure of the turbocharger is lowered.

Even without a signal from the Camshaft Position (CMP) sensor -G40-, the engine will continue to run and can also be re started.

- When a malfunction is detected, the ECM produces one spark for each cylinder on every crankshaft revolution.
- The fact that the ECM 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.

Checking activation

- Push back rubber grommet of connector for Camshaft Position (CMP) sensor -G40- back but leave connector attached.







- Connect LED voltage tester V.A.G 1527 B between receptacle 2 (Camshaft Position (CMP) sensor -G40- signal) and receptacle 1 (B+).

NOTE: Receptacles are numbered accordingly on the back of the connector.

- Operate starter for a few seconds.
- LED should flash.

NOTE: LED voltage testers with a low current consumption continue to glow faintly between activation from the ECM (rather than extinguishing completely) and become much brighter when activated.

If LED does not flash:

Checking power supply







- Disconnect Camshaft Position (CMP) sensor -G40- connector -arrow-.







- Connect multimeter as follows to measure voltage:

Connector Measure to
terminal

1 Engine ground (GND)

- Switch ignition on.
- Specified value: approx. 5 V

Checking signal wire







- Connect multimeter as follows to measure voltage:

Connector Measure to
terminal

2 Engine ground (GND)

- Switch ignition on.
- Specified value: approx. battery voltage (B+).

Checking ground (GND) wire







- Check for open circuit, short to positive, or short to ground in following wiring connections:

Connector Measure to
terminal

3 Engine ground (GND)

- Repair any open/short circuit as necessary.

If the specified values are all achieved and the LED voltage tester does not flash (measured between terminals 1 and 2 with starter connector attached).

- Install a new Camshaft Position (CMP) sensor -G40-.

If the specified values are not obtained:

Check wiring between the Camshaft Position (CMP) sensor -G40- and ECM.

- Connect test box V.A.G 1598/31 to wiring harness for ECM; do not connect directly to ECM. Wiring and Component Testing Using VAG1598/31 Test Box







- Check for open circuit, short to positive, or short to ground in following wiring connections:

Connector Test box VAG 1598/31
terminal Socket

1 (B+) 98
2 (signal) 86
3 (ground) 108

- Repair any open/short circuit as necessary.

If a trial erasure of the DTC memory is followed by the replaced indication of a malfunction relating to the Camshaft Position (CMP) sensor -G40-although all previous tests were OK, the following malfunctions are possible:
- Rotor ring for Camshaft Position (CMP) sensor -G40- misaligned

- Unbolt Camshaft Position (CMP) sensor -G40-and ensure that rotor ring is correctly aligned on camshaft (if it is incorrectly installed, catch will be pressed flat when securing screw is tightened).
- If position of rotor ring is OK, check position of the camshaft in relation to crankshaft.