A/C Relay Circuit Fault

DTC P1650 And/Or P1651 - A/C Relay Circuit Fault:

A/C Relay Circuit Fault (Chart 5 Of 5):

A Quad Driver Module (QDM) is an electronic switch which completes a ground circuit when switched On. The QDM independently controls four separate outputs. A load is connected between battery voltage and the QDM allowing the QDM driver to control the output. Each QDM has fault detection logic which compares QDM driver input and Output voltages. The logic expects to measure less than three volts when the QDM driver is On and greater than seven volts when Off. Each QDM has only one fault line that will detect a fault on any of the four outputs. The Scan tool can be used to cycle each output On or Off. The Scan tool can also perform an automated test which will isolate the faulty output circuit.

DTC Parameters
DTC P1650 arid/or P1651 will set if there is an open short to ground or short to voltage on the QDM output A/C relay circuit.

IMPORTANT: The QDM circuit is continuously checked when the engine is running.

Diagnostic Aids
^ If one output is bad, the PCM will shut down only that QDM output and not the entire quad driver unless the quad driver reaches its thermal limit (short to voltage). At this time it will turn all four quad driver outputs Off. When the quad driver cools down it will turn back On and this process will start over.
^ Check 7.5 AMP IGN 3 fuse in IPJB.
^ A/C relay resistance - 70-90 ohms.
^ Check 30 amp COOL FAN fuse in UHJB.
^ A shorted or open, relay or bulb can cause a DTC P1650/P1651 to set.

Check the tightness of the female terminal grip with a spare male terminal.

Use the scan tool to diagnose the quad driver circuits and perform an off-board QDM test.

For example, if the MIL (SERVICE ENGINE SOON telltale lamp) is Off, the PCM expects to refer to 12 volts on the circuit line. If the circuit is open, zero volts will be measured on the circuit and the fault will be displayed. However, if the lamp is turned On, the PCM expects to measure zero volts on the circuit, and will not detect a fault. This causes an intermittent problem because the lamp is not continuously On.