Set Condition

A signal toggle bit and a signal parity bit are sent by the PCM within the CAN message. In order to be sure the message content is continuously updated, the value of the toggle bit changes from 0 to 1 and vice versa every two messages. In order to be sure that the message content is valid, the parity bit value is set so the sum of specific signal bits of the message content, plus the toggle bit, plus the parity bit is an even number. If the toggle bit value does not change for a calibrated amount of time or the signal parity is not verified for a calibrated amount of time then DTC U0401 is set.