Camshaft Position (CMP) sensor -G40-, checking

WARNING: This page is about a different car, the 2006 Audi A4, 2005 Audi A4, 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying Special Tools - Camshaft Position (CMP) Sensor -G40-, Checking

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Special tools and workshop equipment required

V.A.G 1526 A Multimeter
V.A.G 1527 B Voltage tester
V.A.G 1594 A Connector test kit
V.A.G 1598/31 Test box

Component location → Component locations, overview

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 restarted.

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 intake valve) instead of while the intake 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.

Fig 2: VAG 1527B Voltage Tester Connected Between Sockets 2 And 1

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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 must 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

Fig 3: Locating Connector At Camshaft Position Sensor G40

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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

Fig 4: Identifying 3 Pin Electrical Harness Connector Terminals

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Connect multimeter as follows to measure voltage:

Connector Terminal	Measure to
1	Engine ground (GND)

Switch ignition on.

Specified value: approx. 5 V

Checking signal wire

Fig 5: Identifying 3 Pin Electrical Harness Connector Terminals

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Connect multimeter as follows to measure voltage:

Connector Terminal	Measure to
2	Engine Ground (GND)

Switch ignition on.

Specified value: approx. battery voltage (B+)

Checking Ground (GND) wire

Fig 6: Identifying 3 Pin Electrical Harness Connector Terminals

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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

Connector Terminal	Measure to
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 specified values are not obtained:

Checking wiring between 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. Refer to Electrical testing using VAG1598/31 test box .

Fig 7: Identifying 3 Pin Electrical Harness Connector Terminals

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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

Connector Terminal	Test box V.A.G 1598/31 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 camshaft in relation to crankshaft.

Refer to 15 - ENGINE - CYLINDER HEAD, VALVETRAIN