Description of On-Board Diagnostics

This vehicle is equipped with an electronic transmission control system, which control the automatic shift up and shift down timing, TCC operation, etc. suitably to vehicle driving conditions. TCM has an On-Board Diagnosis system, which detects a malfunction in this system and abnormality of those parts that influence the engine exhaust emission.
When diagnosing a trouble in the transmission including this system, follow "AUTOMATIC TRANSMISSION DIAGNOSTIC FLOW CHART".





TCM in this vehicle has following functions.
- It turns ON "OD/OFF" light for 2 seconds after ignition switch is turned ON for its bulb check and also when OD/OFF switch is ON to let driver know that it is ON.
- When it detects a malfunction which gives a bad influence to vehicle emission, it flashes "OD/OFF" light and at the same time transmits DTC of that malfunction to ECM. (Based on this signal, ECM turns ON MIL and stores freeze frame data then in its memory. For more information, refer to description under Freeze Frame Date.)
- If no malfunction is detected in the next driving cycle after detecting above malfunction, it does not flash "OD/OFF" light or transmit DTC of that malfunction to ECM. If ECM receives no DTC of malfunction for 3 driving cycles continuously, it turns OFF MIL.





Driving Cycle Detection Logic
When a malfunction is detected during the initial driving cycle, it is stored in TCM memory and at the same time TCM transmits a data to inform that a malfunction occurred to ECM. At this time, ECM stores a corresponding pending DTC and freeze frame data in its memory.
(Neither lighting of MIL nor flashing of "OD/OFF" light takes place then.)
If the same malfunction is also detected in the next driving cycle, TCM flashes "OD/OFF" light and ECM lights MIL when it receives a data informing occurrence of a malfunction from TCM.





Freeze Frame Data
ECM stores the engine and driving conditions (in the form of data as shown above) at the moment of the first detection of a malfunction in its memory. This data is called "Freeze frame data".
Therefore, it is possible to know engine and driving conditions (e.g., whether the engine was warm or not, whether the vehicle was running or stopped, whether air/fuel mixture was lean or rich) when a malfunction was detected by checking the freeze frame data. Its use is helpful when rechecking or diagnosing a trouble.