DTC P1640: Control Module Output Circuit: Description

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

The ECM contains an Output Driver Module (ODM) which controls four circuits: A/C relay, main relay, EVAP vent solenoid and EVAP purge solenoid. The ODM controls each of these circuits independently by controlling the circuit ground. The ODM monitors the voltage level at each of the four circuits into the ECM when the device is being commanded on or off. When the device is commanded off (circuit not grounded), the voltage level at the ECM should be high (ignition voltage). When the device is commanded on (circuit grounded), the voltage level at the ECM should be low. Each of the four drivers in the ODM contains a feedback circuit used to determine if a particular circuit failed, which can be read on the Scan tool. DTC P1640 sets when any one of the four feedback voltages is low when that device is turned off or when any one of the four feedback voltages is high when that device is turned on when the engine is running.