Crankshaft Position Sensor

The Powertrain Control Module (PCM) uses dual Crankshaft Position (CKP) "A" and "B" sensors to determine the crankshaft position. The CKP sensor is a three wire sensor based on the magneto resistive principle. A magneto resistive sensor uses two magnetic pickups between a permanent magnet. A reluctor wheel, a slotted ring, machined into the crankshaft, passes the magnets, causes the sensors to return a series of ON and OFF pulses to the PCM. The PCM uses these pulses to decode the position of the engine crankshaft. The PCM supplies each sensor a 12-volt reference, low reference, and a signal circuit. The signal circuit returns a digital ON/OFF pulse 24 times per crankshaft revolution.

The crankshaft reluctor wheel is part of the crankshaft. The notches on the reluctor wheel provide a unique pattern for each pair of cylinders that are at Top Dead Center (TDC) at the same time. This is known as pulse width encoding. This pulse width encoded pattern allows the PCM to quickly recognize which pair of cylinders are at TDC.

Both CKP sensors provide identical pulses, although one signal is shifted several degrees of crankshaft rotation to the other. This amount depends on whether the sensors are separate or integrated with each other. The two CKP signals allow the PCM to perform an angle-based decode operation. This is considered a self-clocked system, where one sensor acts as a clock and the other is a data signal. The advantage of angle-based decoding is the increased accuracy and consistency of signals, even during engine acceleration and deceleration. If one sensor is not operating correctly, the PCM uses a time-based decode operation. This mode will read the pulse width of the remaining signal, and thereby provide a means of back-up with the minimum of performance loss. Diagnostic Trouble Codes (DTCs) are available to accurately diagnose the ignition system with a scan tool.