P1640

DTC P1640:

QDM A Circuit Wiring Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) is used to control several components such as those in the image above. The PCM controls these devices through the use of a Quad-Driver Module (QDM). When the PCM is commanding a component "ON," the voltage potential of the output circuit will be "low" (near 0 volts). When the PCM is commanding the output circuit to a component "OFF," the voltage potential of the circuit will be "high" (near battery voltage). The primary function of the QDM is to supply the ground for the component being controlled.

Each QDM has a fault line which is monitored by the PCM. The fault line signal is available on the data stream for scan tool test equipment display on Tech 1. The PCM will compare the voltage at the QDM based on accepted values of the fault line. If the QDM A fault detection circuit senses a voltage other than the accepted value, the fault line will go from a "low" signal on the data stream to a high" signal and Diagnostic Trouble Code P1640 will set.

DIAGNOSTIC TROUBLE CODE (DTC) P1640 WILL SET WHEN
^ The engine is running.
^ The PCM detects an improper voltage level on a circuit connected to QDM A.
^ The above conditions met for 5 seconds.
^ If the brake is applied QDM A ignores fault.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon) with a current DTC P1640 set. QDM A controls Evaporative Emissions (EVAP) canister solenoid, fan #2, and Torque Converter Clutch (TCC).

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If a QDM related DTC is stored, diagnose that DTC first. The repair made to the related DTC will repair DTC P1640 also.
2. This test will determine which QDM A control device has failed.

DIAGNOSTIC AIDS
Monitor the voltage at each terminal shown above while moving related harness connectors, including PCM harness. If the failure is induced, the voltage will change. This may help locate an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If DTC reoccurs with no apparent connector problem, replace PCM.

NOTICE:
^ PCM is protected by an internal circuit breaker.
^ PCM replacement is not necessary after repairing QDM A quad-driver controlled circuit or component.