Bosch Motronic - Component Datasheet

Crankshaft Position Sensor (G4)

The crankshaft position sensor (aka CPS), referred to as G4 in the schematic is used by the ECU to determine a specific position in the rotational position of the crankshaft. A steel pin is pressed into the flywheel at 62 degrees BTDC for cylinder #1. This pin triggers a reference signal once per engine revolution that the ECU uses to establish a reference point against other signals.

G4 is located on the left side of the engine near the flywheel. It is mounted alongside the crankshaft speed sensor (G28) and care must be taken not to confuse the wiring of these two sensors as they are identical in design.

NOTE - The CPS has a BLACK coloured connector to differentiate it from the other sensor wiring in the engine bay.

If G4 fails, the engine cannot be restarted but if G4 fails whilst the engine is running then it will continue to run by making the fair assumption that the flywheel reference pin has not moved since the engine started !

This sensor is hard to test properly without an oscilloscope to verify that the signal is good, but a useful sanity check is a resistance measurement across pins 1 & 2 of the sensor connector where you should see approx 1000 ohms.

Follow this link for related info on SJM's site, but be advised it may be specific to the 200TQ and UrS4/S6 applications. I'll update this site further in time.