P1600

Circuit Description with 4L30-E Automatic Transmission
A normal function of the Transmission Control Module (TCM) programming is to perform an internal check that verifies the power control relay (internal to the TCM) is functioning correctly.

When the TCM identifies that the power control relay is not functioning properly, then DTC P1600 will set. DTC P1600 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
The ignition switch is in the RUN position.
The TCM high side driver is open.

CONDITION FOR SETTING THE DTC
TCM identifies that the power control relay is not functioning properly.

ACTION TAKEN WHEN THE DTC SETS
^ The TCM flashes the sport mode lamp and sends a MIL request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.
^ The ECM records the operating conditions in the Freeze Frame at the time of the MIL request from the TCM.
^ The transmission operates in the default mode (maximum line pressure, command 4th gear, inhibit TCC, freeze shift adapts).

CONDITIONS FOR CLEARING THE MIL/DTC
^ The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL request.
^ A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the MIL/DTC.
^ The TCM cancels the DTC default mode actions when the ignition switch is Off long enough in order to power down the TCM.

DIAGNOSTIC AIDS
Check the power relay status on the scan tool. The power relay status should display On.

TEST DESCRIPTION

Diagnostic Chart:

The number below refer to the step number on the Diagnostic Table.
2. Performing this step verifies that the power control relay is able to change status.