Important: Do not perform Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission unless one of the concerns noted is present. Failure to follow this procedure could lead to misdiagnosis of the system.

Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission is an organized approach to identifying a condition created by an electronic transmission control system. Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission is intended for use in diagnosing a concern in a vehicle with separate engine and transmission control modules (ECM and TCM).

When a emission-related diagnostic trouble code (DTC) sets as a result of a fault in the transmission, the TCM requests the ECM to illuminate the malfunction indicator lamp (MIL). The ECM may also illuminate the MIL directly. Although both modules may cause the MIL to illuminate, the scan tool can display DTCs from only one module at a time. In addition, the Clear DTC Info command clears DTC data from both modules at the same time. If the DTC failure records are not recorded from both modules before the DTC data is cleared, important diagnostic information may be erased.

Your training and experience as a technician may cause you to focus on either the TCM or the ECM, instead of both modules at the same time. To ensure that both modules are properly diagnosed, separate OBD system checks are included. Diagnostic System Check - Engine Controls identifies DTC status and communication function for the ECM. If no ECM DTCs are present, Diagnostic System Check - Engine Controls will direct you to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission .

Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission identifies DTC status and communication functions for the TCM and the ECM. Both modules are included in Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission because the TCM requires engine data from the ECM in order to run the diagnostics. The ECM diagnostics do not require transmission data in order to run. Correct use of the tables will reduce diagnostic time and prevent the replacement of good parts.

Inspect all of the related wiring and connections including the connections at the TCM, as these may cause an intermittent concern. Inspect the terminals for any damage or any corrosion. Inspect the connector for any pushed-out terminals.

The number(s) below refer to the step numbers on the diagnostic table.

1. Do not perform Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission unless one of the concerns noted is present. Failure to follow this procedure could lead to misdiagnosis of the system.

3. The diagnostic tables in this section are, by design, for use with a Scan Tool . If the Scan Tool is inoperative, you must correct this before beginning any other diagnostic procedures. Do not clear the DTCs unless instructed by a diagnostic procedure.

5. Check for applicable service bulletins before proceeding with the diagnosis.

8. If any multiple DTCs are stored, diagnose the DTCs in the following order of priority:

1.	The ECM DTCs.

2.	The System Voltage DTCs.

3.	Component level DTCs (Sensors, Solenoids, Relays etc.). Diagnose the multiple DTCs within this category in numerical order starting with the lowest DTC number.

4.	The System level DTCs (Misfire, Fuel Trim, etc.).

5.	The Transmission DTCs. Refer to Diagnostic Trouble Code (DTC) List/Type for transmission diagnostics.

When there is a known exception, a DTC table may direct the technician to diagnose a different DTC first.

9. Capturing the stored information will preserve the data that will be lost upon instruction to clear the DTCs at the end of a diagnostic table, or if a TCM disconnect or replacement occurs during a diagnostic procedure. Write down any non-emissions DTCs that are set at this time. Review the captured Information at the end of the diagnostic table in order to catch the next DTC in the event that the multiple DTCs were stored. Follow the order of priority as listed above.

10. Compare the actual control system data with the values in the Scan Tool Data List in order to determine if any parameter is not within limits. Keep in mind that a base engine condition (i.e. advanced cam timing) may substantially alter the sensor values. If the actual data does not correspond with the values in the Typical Scan Tool Data Values table, but the corresponding DTC is not set, this indicates that you have to meet specific conditions before some diagnostics will run. This information is in the supporting text for the DTC table. If you suspect a system fault (Shift Solenoid operation, TCC operation, etc.), refer to the DTCs that apply to that system. The DTC tables are not, by design, for use unless a DTC is set; however, many tables begin with a functional test of the related component. This information can be a useful aid in diagnosis.