Transmission Diagnosis
DTC P0602
Circuit Description with 4L30-E Automatic Transmission
A normal function of the Transmission Control Module (TCM) is to perform an internal test that verifies that the TCM EEPROM has been flashed with diagnostic and shift calibrations. The TCM also verifies that the vehicle-specific application has been locked out from changes. When the TCM detects the absence of software or an unlocked TCM, DTC P0602 sets. DTC P0602 is a type B DTC.
Conditions For Running The DTC
Condition 1:
The ignition is ON.
Condition 2:
The ignition is OFF.
Condition for Setting the DTC
Condition 1:
The TCM EEPROM check sum is incorrect.
Condition 2:
The TCM is unable to write to the EEPROM.
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
DTC P0602 may set immediately after TCM reprogramming.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that an external anomaly, such as Electromagnetic Interference (EMI), did not take place during TCM power up.
3. This step eliminates the TCM software as a possible cause of the DTC. If the DTC continues to set after reprogramming, the fault is in the TCM hardware.