GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Catera 🢒 DTC 🢒 DTC P1600 TCM Internal Watchdog Operation

Circuit Description

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

The number below refer to the step number on the Diagnostic Table.

  1. Performing this step verifies that the power control relay is able to change status.

DTC P1600 TCM Internal - Watchdog Operation

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important:  Before clearing the DTC, use the Scan Tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the ECM/TCM.

  3. Record the DTC Failure Records.
  4. Clear the DTC.
  5. Turn the ignition switch to the OFF position for at least 30 seconds.
  6. With the engine OFF, turn the ignition switch to the RUN position.
  7. Use the Scan Tool device control in order to operate the power control relay ON and OFF several times.

When the power relay is commanded ON and OFF, does the power relay status change to reflect the commanded change?

--

Go to Diagnostic Aids

Go to Step 3

3

Replace the TCM.

Refer to Transmission Control Module Replacement .

Did you complete the replacement?

--

Go to Step 4

--

4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Turn the ignition switch to the RUN position for more than 2 seconds.

Did DTC P1600 reset?

 

Go to Step 1

System OK