The setting of diagnostic code P0642 OBDII is because the vehicle computer has detected a low voltage reference signal for a particular sensor. This sensor has the designation of A and can be related to the transmission, the housing, or a differential.
Usually, this code is accompanied by another sensor code that specifically indicates which sensor is in trouble. P0642 means that the reference circuit voltage is low. Note that if this code appears alone, it may be due to a PCMprogramming error. You must first troubleshoot other set codes before diagnosing and repairing the P0642.