The CKP sensor records inductively the exact angular position of the crankshaft as well as the engine speed.
Sensor ring for the CKP sensor
A Sensor ring, 2.0L Duratorq TDCi
B 1.8L Duratorq-TDCi sensor ring
1 Gap in the sensor ring
The CKP sensor scans a sensor ring with 60โ2 teeth. The gap is located 90 degrees before top dead center of cylinder 3 and is used by the engine management system as a reference mark for the crankshaft position.
The CKP signal is used:
โข to determine engine speed,
โข to synchronize with the CMP signal,
โข to determine the crankshaft position.
Effects of faults
If there is no signal, the engine cannot be started or cuts out.
If the engine does not start, an oscilloscope can be used to check to see if the CKP signal is present when the engine is started.
A frequent cause of starting problems is rust on the CKP sensor and/or on the sensor wheel. Even slight deposits of rust can affect the signal.
Trouble code “Fuel pressure too high”
โข External interference (coming from other electrical sources) can have a negative effect on the CKP signal. This can result in the signal peaks of the CKP sensor being higher than they actually ought to be.
โข The result is that, for example, instead of the system specifying a fuel pressure of 200 bar for engine starting, a fuel pressure of 600 bar is calculated instead and then requested.
โข This fuel pressure request is detected as implausible by the system, whereupon the PCM sets the injected fuel quantity to 0. The engine is therefore prevented from starting.
โข The reason for this is that the CKP signal is transferred unfiltered from the IDM to the PCM and is therefore more susceptible to both internal interference (i.e. from the system itself) and external interference.
โข If a fault of this type occurs, switch ignition to OFF for 3 seconds and then switch on again, repeat starting procedure.
Diagnosis
If a specified maximum time is exceeded after the last CKP signal, there is a fault (plausibility check). This check is capable of analyzing driving errors (engine stalling or cutting out).