DTC P0385: Crankshaft Position Sensor "B" Circuit: Description

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) uses the dual Crankshaft Position (CKP) "A" and CKP "B" sensors in order to determine the crankshaft position. The PCM supplies an ignition voltage and a ground for each sensor. During engine rotation, a slotted ring, machined into the crankshaft, causes the sensors to return a series of ON and OFF pulses to the PCM. The PCM uses these pulses in order to decode the position of the engine crankshaft. The PCM uses 2 basic methods of decoding the engine position: angle-based and time-based, using either CKP "A" or CKP "B" sensor input. During normal operation, the PCM uses the angle-based method. In order to operate in this mode, the PCM must receive the signal pulses from both CKP sensors. The PCM uses the signal pulses in order to determine an initial crankshaft position, and in order to generate the MEDRES (24X reference) and the LORES (4X reference) signals. When the initial crank position is determined, the PCM continuously monitors both sensors for valid signal inputs. As long as both signal inputs remain, the PCM will continue to use the angle-based mode. When either CKP signal is lost, the PCM will compare the MEDRES signal to the Camshaft Position (CMP) sensor signal. If the PCM detects a valid CMP signal, and if the MEDRES to CMP signal correlation is correct, the PCM determines that CKP "A" sensor is at fault. If the MEDRES to CMP correlation is incorrect, the PCM determines that CKP "B" sensor is at fault. If the PCM determines that CKP "B" sensor is at fault, DTC P0385 will set. The PCM will switch from angle-based mode to time-based Mode "A" using the CKP "A" sensor signal input.