CKP - Crankshaft position sensor

3.1) CKP - Crank shaft Position (sensor)

What is it? This is an electrical device that monitors the position of the crank rotation. The output from the CKP allows the ECU to determine the ignition timing, injection timing (in the absence of a cam sensor) and engine speed (revolutions). Generally if an engine has both crank and cam sensors it is the crank sensor that takes care of ignition timing and the cam sensor takes care of injection timing.

Where is it located? Most usually the crank sensor is located on the 'back' of the engine on the edge of the flywheel housing above the starter motor mounting or on the underside of the engine block; although in this position it is much more prone to stone damage, corrosion and dirt. On some engines the crank sensor is to be found on the front of the engine taking its measurements from the crank pulley. In this front position the crank sensor is often more exposed to the effects of dirt, water splash, oil leaks and heat as well as being more awkward to physically access.

How does it work? The device can employ several forms of detector. Some are passive, needing no electrical supply and include; inductive-magnetic (sine wave output), and reed type. These are typified by having just two wires connected to them. Some are active, needing a power source in order to operate and include: magneto-resistance (square wave); Hall-effect (square wave); and optical type. These are typified by having three (or more) wires connected to them.

The magnetic sensor is popular due to its simplicity and reliability, the Hall-effect type is also popular as it also reliable and its design allows for self diagnostic testing. The role of the CKP device is to detect the presence of magnet(s) or marker teeth on the periphery of the reluctor ring on the crank and to send pulse(s) back to ECU. The ECU reads these pulses and electronically triggers a spark at the appropriate point, advancing and retarding the ignition according to the speed of pulses being received. In older engines, perhaps where the cam sensor is absent, the ECU will initiate a spark every time TDC (top dead centre) is detected and each cylinder receives a spark every crank revolution even though ignition is only required on alternate rotations.

Symptoms of faulty crank position sensor

Associated OBD2 error codes DTCs: P0335 - P0339; P1345

• Starting difficulty/failure/stall - If the faulty CKP timing problems are severe they may prevent the engine to fire, to fire and then stall, or stall at some random time without warning.
• Hot engine shut off and failure to restart - The engine may start and run perfectly from cold but will begin to misfire or suddenly shut off after about 15 minutes once the engine has reached operating temperature. This effect is due to thermal expansion of the CKP body causing an intermittent break in electrical continuity and therefore the signal output to the ECU is interrupted. Sometimes the engine will restart but fail again after a further 15 minutes. On other occasions the engine will not restart until it has completely cooled down.

• Misfire - miss-timed spark delivery caused by a faulty CKP signal can cause misfire and back fire events.
• Hesitant acceleration, acceleration ceiling - Miss-timed ignition due to a faulty CKP signal can be exacerbated by increased engine speed. The engine maybe run evenly at idle but will fail to accelerate properly at higher revs until the engine reaches a power ceiling.

NEXT 3.1b) How to check and fix crankshaft position sensors