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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Transmission/Transaxle 🢒 Automatic Transmission - Allison 🢒 DTC P0602

Circuit Description

When the ignition is turned on and the transmission control module (TCM) is powered up or when DTCs are cleared, the TCM performs a self-test to determine if the calibration is valid.

DTC P0602 is a type C DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0602 Transmission Control Module (TCM) Not Programmed

Conditions for Running the DTC
    • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
    • This test will run before any TCM function.

Conditions for Setting the DTC

DTC P0602 sets if the TCM determines the present calibration is invalid.

Action Taken When the DTC Sets
    • The TCM does not illuminate the malfunction indicator lamp (MIL).
    • The transmission is limited to forward range, due to presence of default calibration.
    • The TCM returns to the boot program, and then waits to be calibrated.
    • The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the MIL/DTC

The TCM must be calibrated.

Diagnostic Aids

DTC P0602 may set because of improper TCM reprogramming.

Step

Action

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Failure Records.
  4. Clear the DTC.
  5. Turn OFF the ignition for at least 30 seconds.
  6. Turn ON the ignition.

Did DTC P0602 set again?

Go to Step 3

Go to Diagnostic Aids

3

Perform the transmission control module programming procedure. Refer to Control Module References for replacement, setup, and programming.

Did DTC P0602 set again?

Go to Step 4

Go to Step 5

4

Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 5

--

5

Perform the following procedure in order to verify the repair:

  1. Clear the DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition.
  4. Select Specific DTC.
  5. Enter DTC P0602.

Has the test run and passed?

Go to Step 6

Go to Step 2

6

With the scan tool, observe the stored information, capture info, and DTC Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK