General Motors OBD II systems implement the usual Strategy Based Diagnostic procedures built into the Powertrain Control Module (PCM) and Transmission Control Module (TCM). The first step in diagnosis of a problem on an OBD II system is to identify it as either a trouble code fault (Code Fault) or a driveability symptom (No Code Fault). The OBD II Drive Cycle is used to verify any repair to the system.
OBD II Drive Cycle Procedure
The main intention of the OBD II Drive Cycle is to run the OBD II Main Monitors in order to determine the status of the Inspection & Maintenance (I/M) Readiness Tests. A cold engine startup (e.g., ambient air temperature of 40-100ºF) is a necessary step in preparation to run a complete OBD II Drive Cycle. In most cases the engine coolant temperature must be below 122ºF.
OBD II Drive Pattern
The drive pattern shown below can be used to help solve:
Trouble Code Faults - Refer to the Code List (in this section) or look in electronic media or repair manuals for a code repair chart.
Driveability Symptoms & Intermittent Faults
- Refer to the special repair instructions under No Code Faults in other repair manuals.
Strategy Based Diagnostics
Strategy Based Diagnostics can be used to repair all Electrical and Electronic systems on GM vehicles. The diagnostic approach in this methodology can also be used to solve problems in an OBD II system.