Start Here - Code Will Set If

Diagnostic Chart:

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 high, when that device is turned On, when the engine is running.

DTC PARAMETERS
DTC P1640 will set if A/C relay, Main relay, EVAP vent solenoid, and EVAP purge solenoid feedback voltage is greater than 3.5 volts when that device is commanded On when:
^ Condition exists for longer than 6 seconds
^ Engine is running

DTC P1640 diagnostic runs continuously with engine running.

P1640 is a type B DTC.

DIAGNOSTIC AIDS
To locate an intermittent problem, use Scan to command each of the four devices while monitoring:
^ A/C RELAY CKT SHORT TO VOLTS

OR

^ MAIN RELAY CKT SHORT TO VOLTS

OR

^ EVAP PURGE CKT SHORT TO VOLTS

OR

^ EVAP VENT CKT SHORT TO VOLTS