V50 AWD L5-2.5L Turbo VIN 68 B5254T3 (2005)
Crankshaft Position Sensor: Description and Operation
Engine Speed (RPM) Sensor
The engine speed (RPM) sensor provides the Engine Control Module (ECM) with information about the speed and position of the crankshaft. The
engine control module (ECM) is able to use the signal from the engine speed (RPM) sensor to determine when the piston in cylinder 1 is approaching top
dead center (TDC). However it is unable to use the signal from the engine speed (RPM) sensor to determine whether the piston is in the combustion
stroke or whether the exhaust valve is open (exhaust stroke). The signal from the camshaft position (CMP) sensor is also required to determine the
operating cycle of the engine.
The signal from the engine speed (RPM) sensor is also used to check the engine for misfires. For more information, See, Misfire diagnostic
There is a steel ring with stamped holes welded to the rim of the primary section (the section fixed to the crankshaft) of the flywheel.
The holes are positioned with a gap of 6 degrees between each hole. This arrangement creates a hole for each tooth. There are 360 degrees in one
revolution. 6 degrees between each hole means that there are 60 holes. However two holes are not stamped, to create a reference position (long gap -
missing tooth) for the crankshaft. The first tooth after the reference position is located 84 degrees before TDC on cylinder 1.
The engine speed (RPM) sensor is at the rear of the engine above the flywheel.
The sensor is inductive with a permanent magnet. An alternating current is induced in the sensor when the flywheel/carrier plate passes the engine speed
(RPM) sensor. The generated voltage and frequency increases with the engine speed (rpm). The signal varies between 0.1 - 100 V depending on the
engine speed (RPM).
The Engine Control Module (ECM) is able to determine the engine speed (RPM) by counting the number of holes per time unit. When the reference
position passes the engine speed (RPM) sensor, the voltage and frequency drop momentarily to zero, even though the engine is still running. This allows
the engine control module (ECM) to determine the position of the crankshaft.
If the signal from the engine speed (RPM) sensor is incorrect or missing, the control module will use the signals from the camshaft position (CMP)
sensor, on the condition that the position of the camshaft has been adapted. This means that the car can be driven if the signal is missing.
The engine control module (ECM) can diagnose the engine speed (RPM) sensor. The sensor value (engine speed (rpm)) can be read off using Vehicle
Information and Diagnostics Application (VIDA).
