Chart 1

Diagnostic Chart 1:

Schematic:

The PCM contains an output driver module (0DM) which controls the A/C relay coil circuit ground. The 0DM monitors the feedback voltage level on circuit 459 at the PCM when the device is being commanded On or Off. When the device is commanded Off (circuit not grounded), the voltage level at the PCM should be high (ignition voltage). When the device is commanded On (circuit grounded), the voltage level at the PCM should be low. Chart 1 diagnoses a low circuit voltage fault in which the PCM detected lower than normal feedback voltage when the A/C relay was commanded Off.

DTC PARAMETERS
DTC P1640 will set if A/C relay feedback voltage is less than 4.0 volts when A/C relay is commanded Off when:
^ Condition exists for longer than 6 seconds
^ Engine is running

DTC P1640 diagnostic runs continuously with engine running.

P1640 is a type C DTC.

DIAGNOSTIC AIDS
To locate an intermittent problem, use Scan to monitor A/C RELAY CKT OPEN SHORT TO GND with ignition On, engine Off. When a fault (open or short to ground) exists, the Scan tool will display YES.

A/C relay coil resistance: 70-115 ohms.