Code P1640, QDM "A" Circuit: Notes

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

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

Engine is running.
PCM detects an improper voltage level on a circuit connected to QDM "A".
Above conditions met for 5 seconds.
If brake is applied, QDM "A" ignores fault.

QDM "A" controls EVAP canister solenoid, fan No. 2 and TCC. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE: Test numbers refer to numbers on diagnostic chart.

If QDM related code is stored, diagnose that code first. Repair made to related code will repair Code P1640 also.