ON BOARD DIAGNOSTIC (OBD) SYSTEM

Diagnosis Description

The A/T system has two self-diagnostic systems.
The first is the emission-related on board diagnostic system (OBD-II) performed by the TCM in combination with the ECM. A malfunction is indicated by the MIL (malfunction indicator lamp) and is stored as a DTC in the
ECM memory and in the TCM memory.
The second is the TCM original self-diagnosis indicated by the TCM. A malfunction history is stored in the
TCM memory. The detected items are overlapped with OBD-II self-diagnostic items. For details, Testing and Inspection.

OBD FUNCTION

The ECM provides emission-related on board diagnostic (OBD-II) functions for the A/T system.
One function is to receive a signal from the TCM used with OBD-related parts of the A/T system. The signal is sent to the ECM when a malfunction occurs in the corresponding OBD-related part.
The other function is to indicate a diagnostic result by means of the MIL (malfunction indicator lamp) on the instrument panel. Sensors, switches and solenoid valves are used as sensing elements.
The MIL automatically illuminates in "One or Two Trip Detection Logic" when a malfunction is sensed in relation to A/T system parts. For details, On Board Diagnostic (OBD) System (VQ-37VHR) or On Board Diagnostic (OBD) System (VK-56VD).

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.

Safety Warning

Reading and Clearing Diagnostic Trouble Codes

Use the Manual With the Right Hardware

When to See a Mechanic

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