Diagnostic System Check - Automatic Transmission

CIRCUIT DESCRIPTION
The Powertrain On Board Diagnostic (OBD) System Check is an organized approach to identifying a condition created by an electronic engine control system malfunction. The Powertrain OBD System Check must be the starting point for any driveability concern diagnosis, because it directs the service technician to the next logical step in diagnosing the concern. Understanding the table and using it correctly reduces diagnostic time and prevents the replacement of good parts.

MIL OPERATION
The Malfunction Indicator Lamp (MIL) is located on the instrument panel. The MIL performs the following functions:
^ It informs the driver that a condition has occurred and that the vehicle should be taken for service as soon as possible.
^ As a bulb check and system check, the MIL will illuminate with the ignition ON and the engine not running. When the engine is started, the MIL will turn OFF. If the MIL remains ON, the self-diagnostic system has detected a condition. If the condition goes away, the MIL will turn OFF in most cases, but a diagnostic trouble code will remain stored.
^ If the MIL is illuminated, then the engine stalls, the MIL will remain illuminated as long as the ignition switch is ON.
^ If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Perform the Powertrain On Board Diagnostic System Check first, when the following conditions are present:
^ The MIL does not turn ON when the ignition switch is turned to the RUN position.
^ The MIL remains ON while the engine is running.
^ A driveability problem exists.

IMPORTANT: DO NOT perform this diagnostic if a driveability concern is not present.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Inspect for poor connections at the PCM. Inspect the PCM and harness connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harnesses.

IMPORTANT: This vehicle is equipped with a Powertrain Control Module (PCM) utilizing an Electrically Erasable Programmable Read Only Memory (EEPROM). When diagnostics call for replacement of the PCM the replacement PCM must be programmed.

TEST DESCRIPTION

Steps 1 - 11:

Steps 12 - 14:

The numbers below refer to the step numbers on the diagnostic table.
2. Lack of communication may be due to a partial malfunction of the Class 2 serial data circuit or due to a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
6. This step stores the PCM DTC information into the scan tools memory. Review the captured information at the end of the diagnostic procedure in order to catch the next DTC in the event there are multiple DTCs stored. It is beneficial to review the Freeze Frame and/or Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information and other operating conditions when the DTC set may help diagnose an intermittent condition. Capturing the stored information preserves data that the PCM loses when the following occurs:
^ When you are instructed to clear DTCs.
^ The PCM connectors are disconnected.
^ The PCM is replaced during a diagnostic procedure.
7. The presence of DTCs which begin with U indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
10. If multiple powertrain DTCs are stored, diagnose in the following order of priority:
^ Component level DTCs (sensors, solenoids, relays etc.). Multiple DTCs within this category should be diagnosed in numerical order starting with the lowest numbered DTC, unless otherwise directed.
^ System level DTCs (misfire, fuel trim, etc.)
14. Compare actual control system data with the values in the Engine Scan Tool Data List 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 sensor values.