Code P1640, QDM No. 1 Circuit: Notes

Control module controls several components as shown in wiring schematic. Control module controls these devises through use of a Quad-Driver Module (QDM). When control module is commanding a component on, voltage potential of output circuit will be low (near zero volt). When control module 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 control module.Fault line signal is available on data stream for scan tool test equipment display on Tech 1. Control module will compare voltage at QDM based on accepted values of fault line. If QDM No. 1 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. Control module will illuminate Malfunction Indicator Light (MIL).

1. If QDM related code is stored, diagnose that code first. Repair made to related code will repair Code P1640 also.
2. If QDM No. 1 symptoms are present, checks on chart 2 of 2 should isolate cause of fault.
3. This test will determine which circuit is out of specifications.
4. This test will determine if problem is circuit or component.