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Home >> Mazda >> 2001 >> 626 ES V6-2.5L DOHC >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Description of On-Board Diagnostics >> Description of the On-Board Diagnostic (OBD) Test

Description of the On-Board Diagnostic (OBD) Test




FOREWORD
- When the customer reports a vehicle malfunction, check the malfunction indicator lamp (MIL) indication and diagnostic trouble code (DTC), then diagnose the malfunction according to following flowchart.
- If a DTC exists, and the MIL does not illuminate or flash, diagnose the applicable symptom troubleshooting.
- If no DTC exists and the MIL does not illuminate or flash, diagnose the applicable symptom troubleshooting.

OBD-II DESCRIPTIONS
- Use the NGS tester for diagnosis on OBD-II equipped vehicles. The NGS tester has a generic scan tool function that is standard across the automotive industry in the United States. It also performs the manufacture's specific functions; that is, the NGS tester can perform various functions according to the vehicle and program card selected.

OBD-II GENERIC FUNCTION
- Use these functions by selecting "GENERIC OBD II FUNCTIONS" from the NGS tester menu screen. These functions enable you to monitor on-board diagnostic system data and DTCs that are related to emissions, as defined and fixed by OBD-II regulations. These functions are found even in commonly marketed scan tools and are called "generic functions".

OBD-II SPECIFIC FUNCTION
- "Specific functions" are original scan tool functions created by various manufactures in order to be able to troubleshoot effectively. When using these functions, the correct vehicle model and program card must be selected.

OBD-II PENDING TROUBLE CODES
- The following functions are generic functions.
- These appear when a problem is detected in a monitored system. The MIL is illuminated when a problem is detected in two consecutive drive cycles. The code for a failed system is stored in the PCM memory in the first drive cycle. This code is called the pending code. If the problem is not found in the second drive cycle, the PCM judges that the system returned to normal or the problem was mistakenly detected, and deletes the pending code. If the problem is found in the second drive cycle too, the PCM judges that the system has failed, deletes the pending code, illuminates the MIL and stores the DTC.

OBD-II FREEZE FRAME DATA
- This is the technical data which indicates the engine's condition at the time of the first malfunction. This data will remain in the memory even if another emission-related DTC is stored, with the exception of the Misfire or Fuel System DTCs. Once freeze frame data for the Misfire or Fuel System DTC is stored, it will overwrite any previous data and the freeze frame will not be overwritten again.

OBD-II ON-BOARD SYSTEM READINESS TEST
- This shows OBD-II systems operating status. If any monitor function is incomplete, NGS tester will identify which monitor function has not been completed. Misfires, Fuel System and Comprehensive Components (CCM) are continuous monitoring-type functions and will display a "CONT" message on the screen of the NGS tester. The catalyst, EGR system, evaporation system and oxygen sensor will be monitored under drive cycles. The NGS tester will display a "YES" message once those system monitor functions are completed. The OBD-II diagnostic system is initialized by performing the DTC cancellation procedure or disconnecting the negative battery cable.

OBD-II DIAGNOSTIC MONITORING TEST RESULTS
- These results from the intermittent monitor system's technical data, which are used to determine whether the system is normal or not. They also display the system's thresholds and diagnostic results. The intermittent monitor system monitors the oxygen sensor, evaporative purge system, catalyst and the EGR system.

OBD-II READ/CLEAR DIAGNOSTIC TEST RESULTS
- The following functions are generic functions.
- This retrieves all stored DTCs in the PCM and clears the DTC, Freeze Frame Data, On-Board Readiness Test Results, Diagnostic Monitoring Test Results and Pending Trouble Codes.

OBD-II 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. Since PID values for output devices are PCM internal data values, perform the Simulation Test to identify which output devices are malfunctioning.

KEY ON ENGINE OFF (KOEO) SELF-TEST
- Key On Engine Off (KOEO) Self-Test is a functional test of the powertrain control module performed on demand with the key on and the engine off. This test will perform checks on certain sensor and actuator circuits. A fault must be present at the time of testing for the KOEO Self-Test to detect the fault. When a fault is detected, a Diagnostic Trouble Code (DTC) will be output on the data link at the end of the test when requested by a scan tool.

KEY ON ENGINE RUNNING (KOER) SELF-TEST
- Key On Engine Running (KOER) Self-Test is a functional test of the powertrain control module performed on demand with the key on engine running and vehicle stopped. A check of certain inputs and outputs is made during operating conditions and at normal temperature. The brake pedal position, transmission control and power steering switch tests are part of KOER On-Demand Self-Test and MUST be performed during this operation if applicable. These are described below. A fault must be present at the time of testing KOER On-Demand Self-Test to detect the fault. When a fault is detected, a Diagnostic Trouble Code (DTC) will be output on the data link at the end of the test when requested by a scan tool.

Brake On/Off Test
- This tests the ability of the powertrain control system to detect a change of state in the stoplight switch. Brake pedal MUST briefly be applied and released on all vehicles equipped with Brake Pedal Position input. This is done during KOER On-Demand Self-Test.

Transaxle Control Switch Test
- This tests the ability of the powertrain control system to detect a change of state in the O/D OFF switch. Switch MUST briefly be cycled on all vehicles equipped with O/D OFF switch. This is done during KOER On-Demand 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 on vehicles equipped with a power steering pressure (PSP) switch or sensor. This is done during KOER On-Demand Self-Test.

CONTINUOUS MEMORY SELF-TEST
- Testing for Continuous Memory DTCs is a functional test of the powertrain control module performed under any condition (engine running or off) with the key on. Unlike the KOEO and KOER self tests, which can only be activated on demand, the Continuous Self Test is always active. A fault does not need to be present at the time of testing for Continuous DTCs and is therefore, especially valuable when diagnosing intermittent faults. This test will detect failures contributing to drivability or emission concern. The vehicle may need to be driven or the OBD-II Drive Cycle completed to allow the PCM to detect a fault. When a fault is stored in memory, a Diagnostic Trouble Code (DTC) will be output on the data link at the end of the test when requested by a scan tool.
- There are two types of Continuous DTCs. The first type is an emission related malfunction indicator lamp (MIL) code in the instrument cluster. The second is a non emission related non-MIL code which will never illuminate the cluster indicator.
- For emission related MIL codes, the PCM will store the DTC in continuous memory when a fault is detected for the first time. At this point the DTC will not illuminate the MIL and is now considered a pending code. The purpose of pending codes is to assist in repair verification by reporting a pending DTC after one drive cycle. If the same fault is detected after the next ignition start-run cycle, the emission related MIL code will illuminate the MIL. The MIL will remain on even if the fault is intermittent. The MIL will be extinguished if the fault is not present through three consecutive drive cycles or a PCM reset is performed. Also, an emission related pending MIL and non emission related non-MIL code will be erased after approximately 40-80 vehicle warm-up cycles or a PCM reset.
- Any scan tool that meets OBD-II requirements can access Continuous Memory to retrieve emission related MIL DTCs. However, not all scan tools access pending and non emission related non-MIL DTC's in the same way. If using the NGS tester, all MIL (including pending) and non-MIL codes are retrieved together on the same screen.
- During most diagnostic procedures, it is required that all DTCs be retrieved and cleared. Consult the instruction manual from the tool manufacturer for specific instructions.
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