Bosch Motronic - Component Datasheet

Engine Speed Sensor (G28)

The Engine Speed Sensor (ESS), referred to as G28 on the schematic, is used by the ECU to determine the engine speed. It does this by generating a saw-tooth waveform as teeth on the flywheel induce a voltage across the tip of the sensor. The ECU counts the number of these pulses over time and calculates the instantaneous engine speed.

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

Note - the ESS device has a GREY coloured connector to differentiate itself from others in the engine bay.

If G28 fails, the engine cannot be restarted.

Like G4, the ESS is tricky to test properly without that oscilliscope but again you should see approx 1000ohms across pins 1 & 2 for a quick check.