Impulse / speed reference sensor. Porsche 911 84-89

also known are Engine Crankshaft Position Sensor

The engine crankshaft position sensor (CPS) is a critical component that monitors the crankshaft’s position and rotational speed. It sends this data to the engine control unit (ECU), allowing precise control of fuel injection, ignition timing, and other key engine functions. Without accurate input from the CPS, the ECU cannot properly synchronize spark or fuel delivery—leading to poor performance or even a no-start condition.

Crankshaft sensors typically use magnetic or Hall-effect technology:

Magnetic sensors generate a signal with a coil and magnet as the crankshaft rotates.

Hall-effect sensors detect changes in the magnetic field using a semiconductor for highly accurate readings.

Depending on the engine design, the CPS is usually located near the crankshaft pulley, harmonic balancer, flywheel, or transmission. It reads notches or teeth on a tone wheel to create a signal the ECU can interpret.

Over time, heat, vibration, and contaminants (oil, dirt, or metal shavings) can cause the sensor to fail. When this happens, common symptoms include engine stalling, rough idling, misfires, or a no-start condition.

• Porsche 911 1984-1986 3.2L
• Porsche 911 1987-1989 3.2L G50
• Porsche 911 1978-1989 3.3L Turbo (930)

Common Symptoms of a Failing Crankshaft Position Sensor

·         No Start Condition – If the ECU doesn’t receive a proper signal, the engine won’t start.

·         Stalling When Warm – The sensor may fail when the engine reaches operating temperature, causing unexpected stalling.

·         Erratic or Dead Tachometer – In some vehicles, a faulty CPS can cause the tachometer to behave irregularly.

·         Check Engine Code P0335 – A failed internal circuit may trigger this code, though not always.

·         Poor Performance at Certain RPMs – Timing issues can cause hesitation, especially at idle or higher RPMs.

·         Multiple Cylinder Misfires – Unlike a single bad coil or injector, CPS failure can cause misfires across all cylinders.