Description of the On-Board Diagnostic (OBD) Test

ON-BOARD DIAGNOSTIC TEST DESCRIPTIONS
The OBD Test is divided into three special tests:
- Key On Engine Off Self-Test (KOEO)
- Key On Engine Running Self-Test (KOER)
- Continuous Memory DTCs Self-Test.

The OBD test checks the integrity and function of the powertrain control system and outputs the test results when requested by the New Generation Star (NGS) tester. It also provides a quick end check of the powertrain control system. It is usually performed at the start of each diagnostic procedure with all the accessories off and is performed at the end of most troubleshooting tests for verification of repair and to make sure no other faults were incurred while servicing a previous fault.

SYSTEM PASS
A system pass will be displayed when no Diagnostic Trouble Codes (DTC)s are output and no NGS Tester communication error exists. System pass means that hardware monitored by the Powertrain Control Module (PCM) is functioning within normal operating limits. When using the NGS Tester, all step by step instructions are defined in the NGS instruction manual. When using a generic scan tool, KOEO and KOER self-tests may not be supported. Refer to the manufacturer's manual for details.

KEY ON ENGINE OFF (KOEO) SELF-TEST
Key On Engine Off is a functional test of the PCM performed on demand. A fault must be present at the time of testing for the Self-Test to detect the fault. This test will perform checks on certain sensor and actuator circuits. A DTC will be output on the data link at the end of the test when requested by the NGS Tester. Only system pass, hard fault code or an incomplete OBD II drive mode will be displayed.

KEY ON ENGINE RUNNING (KOER) SELF-TEST
Key On Engine Running is a functional test of the PCM performed on demand with the engine mining and vehicle stopped. A check of the inputs and outputs is made during operating conditions and at normal temperature. The brake on/off, transaxle control and power steering pressure switch tests are part of the KOER self-test and MUST be performed during this operation (see below). A fault must be present at the time of testing to detect the fault. A DTC will be output on the data link at the end of the test when requested by the NGS Tester. Only system pass, hard fault code or an incomplete OBD II drive mode will be displayed.

RETRIEVE / CLEAR CONTINUOUS MEMORY DTC ACCESS SELF-TEST
Continuous DTC access is also a functional test of the powertrain control system. The continuous self-test is always active. The test consists of all the OBD II monitors and the comprehensive component monitor, and is designed to detect failures contributing to driveability and emission concerns. As part of the OBD Test, the technician may perform a specific drive cycle before running the OBD Test. This is necessary to detect certain faults not tested during other self-test operations. All self-tests are menu driven in the NGS Tester.

PARAMETER IDENTIFICATION (PID) ACCESS
The PID mode allows access to certain data values, analog and digital inputs and outputs, calculated values and system status information.

BRAKE ON / OFF TEST
This tests ability of the powertrain control system to detect a state of change in the stop light switch. The brake pedal MUST briefly be applied and released on all vehicles with brake on/off input. This test is done during the KOER self-test.

TRANSAXLE CONTROL (OD OFF) SWITCH TEST
This tests ability of the powertrain control system to detect a state of change in the O/D OFF switch. The switch MUST briefly be cycled on all vehicles with an O/D 0FF switch. This test is done during the KOER self-test.

POWER STEERING PRESSURE (PSP) SWITCH TEST
This tests the ability of the powertrain control system to detect a change in power steering fluid pressure. The steering wheel MUST briefly be turned at least 1/4 of a revolution. This test is done during the KOER self-test.