Description of On-Board Diagnostics
ON-BOARD DIAGNOSTIC SYSTEM TEST DESCRIPTIONSQuick Test Description
Quick test is divided into three special tests, Key ON engine off Self-Test, Key ON engine running Self-Test and Continuous Memory DTC access. Quick test also provides a quick check of the powertrain control system and is usually performed at the start of each diagnostic procedure and at the end of most pinpoint tests for verification of repair and to ensure no other faults exist.
Key On Engine Off Self-Test
Key ON engine OFF is a functional test of the powertrain control system performed on demand. A fault has to be present at the time of testing for the key on engine Self-Test to detect the fault. When a fault is detected, a Diagnostic Trouble Code (DTC) will be output on the data link when requested by a scan tool.
Key ON Engine Running Self-Test
Key ON Engine Running is a functional test of the powertrain control system performed on demand with the engine running and vehicle stopped. A check of the inputs and outputs is made during operating conditions and at normal temperature. A fault has to be present at the time of testing. When a fault is detected, a Diagnostic Trouble Code will be output on the data link when requested by scan tool.
Continuous Memory DTC Access Self-Test
Continuous Memory 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 Quick Test, the technician may perform a specific drive cycle before running quick test. This is necessary to detect certain faults not tested during other self-tests operations. All self-test are menu driven in the New Generation Star (NGS) scan tool.
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
The brake pedal MUST be depressed and released after key ON engine running self-test is initiated.
Transmission Control Switch Test
On vehicles equipped with a transmission control switch (TCS), the switch MUST be cycled after key ON engine running self-test is initiated.
Wiggle/Tap Test
The wiggle/tap test is performed by the technician in an attempt to re-create an intermittent fault.