Improper adjustment or operation of the ASCD brake switch can cause the Automatic Speed Control Device (ASCD) to “not set” and/or DTC P0605 (ECM) to store. If a malfunction in the ASCD system is detected, the CRUISE indicator may stay ON and the “SET” indicator may flash.
Before replacing the Engine Control Module (ECM) for a DTC P0605, check the ASCD brake switch for proper operation and adjustment. Refer to the appropriate Service Manual for ASCD brake switch operation and adjustment information for the year and model. The key part of this procedure is checking to make sure the clearance gap of the switch is adjusted correctly.
Courtesy of Mitchell 1.