For 1990-2009 cars

### Circuit Description

The TCM performs various internal tests. Some of these tests include checks on data integrity, memory performance, and the Transmission Power Relay control circuits. If the TCM detects a problem in any of these areas, a DTC will set.

### Conditions For Running The DTC

Once at power up.

### Conditions For Setting The DTC

The TCM detects an internal problem.

### Action Taken When the DTC Sets

• | The TCM illuminates the Service Transmission Lamp (STL) 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.

### Conditions for Clearing the MIL/DTC

• | The TCM turns off the STL as soon as the fault is no longer present.

• | 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.

### Diagnostic Aids

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

• | Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step ensures that the fault is present.

#### DTC P1605 - TCM Internal Error

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Start the engine.
4. Operate the vehicle within the conditions required for this diagnostic to run. Refer to Conditions for Running the DTC.
5. Check for any DTCs.

Is DTC P1605 set?

--

Go to Step 3

Go to Step 4

3 | Replace the TCM. Refer to Automatic Transmission, On Vehicle Service, TCM . Is the action complete? | -- | Go to Step 4 | --
4 | Were there any additional DTCs noted during the Powertrain or Transmission OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | Go to Step 5
5 | Does the Transmission now function properly? | -- | System OK | Go to Functional Test