Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
OBD-II Overview
The goal of the On Board Diagnostics-II (OBD-II) regulation, which was mandated by the Environmental Protection Agency (EPA), is to ensure proper emission system operation for the life of the vehicle by providing the vehicle with an "on-board" diagnostic system which is capable of continuously monitoring the efficiency of the emission control system.
To achieve this goal, OBD-II diagnostics monitors emissions-related components and systems for deterioration and identifies an emissions-related malfunction before the driver notices a problem with the vehicle.
The ECM illuminates the Malfunction Indicator Light (MIL) and stores a Diagnostic Trouble Code (DTC) for some failures in the Emissions System. The DTCs are retrieved using SST connected to the standardized OBD-II Data Link Connector (DLC) located below the left side of the instrument panel.
OBD-II diagnostics supports not only the standard test mode of OBD-II (Mode 01 -Mode 07) but also an advanced test Mode (Mode 22: Supported PID - analog inputs and outputs, digital inputs and outputs). All of these diagnostic test modes are supported using SST through the DLC.
The ECM executes the following key monitoring for OBD-II:
- Primary emission control system/components
- Heated oxygen sensors (includes heater)
- Catalyst
- Fuel system
- Evaporative emission system
- Misfire
- Comprehensive components (input and output)
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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