Diagnostic System Check - Vehicle
All vehicle diagnostic procedures are organized in a logical structure that begins with the Diagnostic System Check - Vehicle, refer to
Diagnostic System Check - Vehicle. The Diagnostic System Check -
Vehicle must always be referred to first, as you will be directed through the logical steps necessary to diagnose any vehicle electrical fault condition.
Vehicle system diagnostic tables locate a faulty circuit or component through a logical approach, based on a process of elimination. These diagnostic tables are developed with the following assumptions:
| • | The vehicle functioned correctly at the time of assembly. |
| • | There are no multiple faults. |
| • | The problem currently exists. |
An understanding of and the correct use of the diagnostic tables is essential if the diagnostic time is to be minimized and/or to prevent poor diagnosis.
Symptoms Diagnostics
Provided all of the following conditions exist, refer to
Symptoms - Automatic Transmission :
| • | An automatic transmission fault condition exists |
| • | There is no Current Diagnostic Trouble Code presently stored in the ECM |
| • | All the Tech 2 automatic transmission data parameters are within the normal operating range |
Diagnostic Trouble Code (DTC) Tables
Through the process of completing the Automatic Transmission Diagnostic Circuit Check, you will be directed to the Diagnostic Trouble Code (DTC) Tables if there is a DTC currently stored in the Transmission Control Module (TCM).
Multiple DTCs Fault Condition
In any given electronic system, some fault conditions trigger multiple component DTCs even if the fault condition exists only in a single component. If there are multiple DTCs stored in the TCM, the Technician must view and record all DTCs logged.
The relationship between the logged DTCs can then be reviewed to determine the source of the fault condition. Always begin the diagnostic process by completing the Diagnostic Table for the fault condition that may trigger other DTCs to set.
The following fault conditions may trigger multiple DTCs:
| • | A system voltage that is too low may cause incorrect automatic transmission system management operation or a component to malfunction |
| • | A system voltage that is too high may damage the TCM and/or other sensitive automatic transmission components |
| • | A fault condition in the TCM Read Only Memory (ROM) or Random Access Memory (RAM) |
| • | A fault condition in the TCM internal circuitry or programming |
| • | An improperly connected sensor or component wiring harness connector |
| • | An electrical fault condition in shared TCM electrical circuits may trigger DTCs for components or sensors that are connected to the same faulty circuit (e.g. open in one of the GMLAN circuits). Test the electrical circuit of the appropriate sensors
or components to isolate the fault condition. |
If there are no obvious faults to begin a multiple set DTC fault condition, always start with the lowest number, then work progressively through each.
