Code P1640, QDM No. 1 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 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.

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 No. 1.
Brake not applied.
Above conditions met for 5 seconds.

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.
If QDM No. 1 symptoms are present, checks on chart 2 of 2 should isolate cause of fault.
This test will determine which circuit is out of Specifications.
This test will determine if problem is circuit or component.
As the factory installed PCM is protected with an internal circuit breaker, it is highly unlikely that PCM needs to be replaced.