Editor’s note: This article is based on information from March 1, 2009. While the core principles of Global OBD2 scanners remain relevant, always consult up-to-date resources for the latest vehicle diagnostic procedures.
Every auto repair shop, whether a dealership or an independent service center, includes Check Engine Light diagnostics as a standard service. Many of these facilities service a wide range of vehicle brands and often rely on a single, versatile aftermarket scan tool. These tools, while sometimes offering enhanced capabilities for specific manufacturers, are fundamentally designed to access standardized diagnostic information across all vehicles. This universal access is achieved through the “Global OBDII” function, a key feature in any Global Obd2 Scanner, ensuring compatibility regardless of the vehicle’s make.
Understanding OBD2 Basics
The Engine Control Module (ECM) in any vehicle compliant with OBDII standards has a primary mission: maintaining optimal vehicle emissions. It achieves this by meticulously managing and monitoring every system that influences these emissions. Consequently, every powertrain-related Diagnostic Trouble Code (DTC) is, in some way, linked to emissions control.
OBDII was developed to overcome limitations of earlier onboard diagnostic systems. It brought about crucial improvements, including standardized code formats and universal code definitions. The Data Link Connector (DLC) was also standardized, ensuring any global OBD2 scanner could interface with any compliant vehicle. Furthermore, OBDII significantly enhanced the ECM’s diagnostic capabilities, moving beyond basic circuit checks to include functional and rationality testing of emissions-related components and systems.
Diagnostic data became more consistent, with the adoption of common Parameter Identifications (PIDs) across different manufacturers, simplifying diagnostics for technicians. Additional modes were incorporated to assist technicians, who might not have access to Original Equipment (OE) level information or specialized scan tools, in effectively diagnosing faults identified by the ECM. Thanks to the efforts of organizations like the National Automotive Service Task Force (NASTF), vital OE information, once considered proprietary, is now readily available. This level of accessibility was not always the case when OBDII was first introduced.
Currently, there are nine distinct modes accessible when utilizing the Global OBDII (it’s important to differentiate this from Generic OBDII) function on your aftermarket scan tool. A significant portion of Check Engine Light issues encountered daily can be effectively diagnosed and resolved using the data provided by these nine modes, highlighting the power and versatility of a global OBD2 scanner.
Mode 1: Monitor Status and Real-Time Data
Mode 1 is your gateway to understanding the status of onboard monitors. Each monitor is linked to a specific system or component that can affect vehicle emissions. Monitors are categorized as either continuous or non-continuous. Continuous monitors include the comprehensive component monitor, the misfire monitor, and the fuel system monitor. All other monitors fall into the non-continuous category.
Each monitor performs a test, or a series of tests, to evaluate the operational health of its associated system or component. The monitor status screen of your global OBD2 scanner simply indicates whether all tests within a given monitor have been completed. Ideally, all monitors should display “Ready or complete” after testing. If a vehicle does not utilize a particular monitor, the display will show “Not supported or not available.”
A “Not Ready” or “Not Complete” status for any monitor suggests a few possibilities. It could mean that DTCs were recently cleared using a scan tool, which resets the monitors, or that the ECM has experienced a loss of battery power. This status itself can be a diagnostic clue. If power loss is due to a wiring problem or a failing battery, the ECM may be constantly rebooting, potentially leading to drivability issues. Therefore, checking monitor status with a global OBD2 scanner is a crucial first step.
Beyond monitor status, Mode 1 also provides access to Current Data, often referred to as Live Data. This screen displays real-time PID information. Unlike some enhanced, manufacturer-specific PIDs, Global OBDII PIDs present ACTUAL data. Consider the Engine Coolant Temperature (ECT) PID as an example. Because ECT is vital for fuel control, some manufacturers might substitute a data value in enhanced mode if the true ECT reading is questionable. However, in Global mode, your global OBD2 scanner will display the true, unfiltered ECT reading, regardless of its validity.
Mode 2: Freeze Frame Data
Freeze Frame captures a snapshot of available data PIDs recorded by the ECM at the exact moment a DTC is registered. This information is invaluable for diagnostics, as it helps recreate the conditions present when the fault code was triggered. When using a global OBD2 scanner, Freeze Frame becomes a crucial tool in understanding the context of the problem.
Freeze Frame is particularly useful when diagnosing codes related to continuous monitors because these codes can be set under a wide range of engine load and RPM conditions. Freeze Frame data for non-continuous monitor related codes usually reflects the specific conditions required by the ECM to run the relevant test.
Mode 3: Stored Diagnostic Trouble Codes (DTCs)
Mode 3 is where your global OBD2 scanner reveals a list of all DTCs that have been set and have caused the ECM to illuminate the Malfunction Indicator Lamp (MIL), commonly known as the Check Engine Light. These codes can represent a first-time fault (“1-trip” code) or a repeated fault (“2-trip” code).
Even after a code has been set, the ECM continues to perform tests. If a previously failed test now passes for three consecutive cycles, the ECM will turn off the MIL. However, the code will remain stored in Mode 3. A global OBD2 scanner will still retrieve these stored codes even after the light has gone out.
After a predetermined number of warm-up cycles without a recurrence of the fault, the code will be automatically erased from the ECM’s memory. This is a common scenario when a customer schedules a Check Engine Light diagnosis, but by the time they arrive, the light is no longer illuminated. Despite the light being off, Mode 3 of your global OBD2 scanner might still hold crucial clues to the underlying issue.
Mode 4: Clearing Diagnostic Trouble Codes
Once repairs are complete and you are ready to verify the fix, Mode 4 of your global OBD2 scanner is used to clear the DTCs from the ECM’s memory. However, it’s crucial to use this function only when you are confident in your repair. Clearing codes also resets all monitors and erases any existing test results they contain. Therefore, clear codes only after confirming the repair with your global OBD2 scanner and any necessary test drives.
Mode 5: Oxygen Sensor Monitor Test Results
Mode 5 provides access to the tests and their results used by the ECM to verify the correct operation of the oxygen sensors. When facing diagnostic challenges, such as investigating the cause of a catalytic converter efficiency code, Mode 5 on your global OBD2 scanner can be incredibly helpful.
Because these tests often rely on data from the oxygen sensors themselves, a faulty sensor can skew the results and potentially be the root cause of the DTC. Examining Mode 5 test results, if available for the vehicle, can aid in confirming the health of the oxygen sensors. If Mode 5 is not supported, Mode 6 becomes even more critical.
Mode 6: Non-Continuous Monitor Test Results
Mode 6 is unique in that it presents the individual tests and their outcomes for every non-continuous monitor. Historically, this information was often obscured, requiring interpretation and conversion before technicians could use it effectively. However, modern aftermarket service information systems now typically list the test identifications and descriptions, making Mode 6 data from a global OBD2 scanner much more user-friendly and valuable.
On older Ford vehicles, Mode 6 also included misfire monitor test results, even though the misfire monitor is classified as continuous. Vehicles utilizing Controller Area Network (CAN) protocols also include misfire monitor results in Mode 6. Furthermore, CAN-based vehicles feature enhanced Mode 6 data screens that are pre-translated and converted into readily understandable data, further improving the diagnostic capabilities of a global OBD2 scanner.
Mode 7: Continuous Monitor Test Results
Many aftermarket scan tools label Mode 7 as Pending Codes. This mode records any “2-trip” codes related to continuous monitors that the ECM has failed once. Mode 7 in your global OBD2 scanner can be used to validate repairs for these codes. By clearing the ECM and then test-driving the vehicle under conditions similar to those recorded in the original Freeze Frame, you can check if the code reappears in Mode 7. Some later OBDII vehicles, and all CAN vehicles, will also record the initial fault of non-continuous monitor related codes in Mode 7, expanding its diagnostic utility when used with a global OBD2 scanner.
Mode 8: Request Control of Onboard Systems
Currently, Mode 8 functionality is primarily limited to the EVAP system, and even then, only on certain vehicles. If available, Mode 8 on your global OBD2 scanner allows you to seal the EVAP system by closing the canister vent valve. This enables you to perform vacuum or pressure tests to check for leaks within the system.
Mode 9: Vehicle Information
Mode 9 provides essential vehicle information, including the Vehicle Identification Number (VIN) and the ECM’s calibration details. Given that many drivability problems are linked to software issues, this information can help determine if the ECM requires reprogramming or reflashing. A mismatched VIN, potentially due to a junkyard ECM replacement, can also be identified through Mode 9, preventing misdiagnosis. While enhanced modes often require extensive input before connection, Global OBDII connection through a global OBD2 scanner is generally quicker and simpler, requiring less preliminary information.
By understanding these nine modes and leveraging the capabilities of a global OBD2 scanner, technicians and even car owners can effectively diagnose a wider range of powertrain-related codes, leading to faster and more accurate vehicle repairs. Investing in a quality global OBD2 scanner is an investment in efficient and comprehensive vehicle diagnostics.
