On-Board Diagnostic System Description

GENERAL DESCRIPTION
The automatic transmission control system in this vehicle is controlled by TCM. TCM has an On-Board Diagnostic system which detects a malfunction in this system and abnormality of those parts that influence the engine exhaust emission.
When diagnosing automatic transmission troubles, be sure to have full understanding of the outline of ON-BOARD DIAGNOSTIC SYSTEM and each item in PRECAUTION IN DIAGNOSING TROUBLE and execute diagnosis according to AUTOMATIC TRANSMISSION DIAGNOSTIC FLOW TABLE.

ON-BOARD DIAGNOSTIC SYSTEM





For automatic transmission control system, TCM has the following functions.
- When the ignition switch is turned ON with the O/D cut switch turned OFF and no malfunction in A/T control system detected, the "O/D OFF" lamp lights for about 2 sec. after the ignition switch is turned ON and then goes OFF for the bulb check. If the O/ D cut switch is ON at this time, however, "O/D OFF" lamp remains ON to let driver known that gear is not shifted to overdrive gear (4th gear).
- When a malfunction in A/T control system (and/or a malfunction which gives an adverse affect to vehicle emission) is detected, it flashes "O/D OFF" lamp, stores the malfunction DTC and at the same time transmits DTC of that malfunction to ECM. (Based on this signal, ECM turns ON malfunction indicator lamp (MIL, "CHECK ENGINE" lamp) and stores DTC/freeze frame data then in its memory.)
- If no malfunction is detected in the next driving cycle after detecting above malfunction, TCM does not flash "O/D OFF" lamp and does not transmit DTC of that malt unction to ECM, however, DTC stored in TCM memory will remain.
If ECM receives no DTC of malfunction for 3 driving cycles continuously, it turns OFF MIL although DTC stored in ECM memory will also remain.

Freeze Frame Data
Refer to the same item under Powertrain Management; Computers and Control Systems.

2 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 in its memory.
(Neither lighting of MIL nor flashing of "O/D OFF" light takes place then.)
If the same malfunction is also detected in the next driving cycle, TCM flashes "O/D OFF" light and ECM lights MIL when it receives a data informing occurrence of a malfunction from TCM.

PRECAUTION IN DIAGNOSING TROUBLE
- Don't disconnect couplers from ECM, battery cable from battery, ECM ground wire harness from engine or main fuse before checking the diagnosis information (DTC, freeze frame data, etc.) stored in ECM memory. Such disconnection will clear memorized information in ECM memory.
- Using SUZUKI scan tool or OBD-II generic scan tool, the A/T diagnostic information stored in ECM memory can be checked and cleared as well. Before its use, be sure to read Operator's (Instruction) Manual supplied with it carefully to have good understanding of its functions and usage.
- DTC stored in TCM can not be cleared by using ECM (OBD-II) application of SUZUKI scan tool in Mass storage cartridge or OBD-II generic scan tool. Be sure to follow DTC clearance procedure under "How to Clear Diagnostic Trouble Codes" when clearing it.
- Priorities for diagnosing troubles
If two or more Diagnostic Trouble Codes (DTCs) are stored, proceed to the flow table (chart) of the DTC which was detected earliest in the order and follow the instruction in that table (chart).
If no instructions are given, troubleshoot diagnostic trouble codes according to the following priorities.
1. Diagnostic Trouble Codes (DTCs) other than DTC P0171/ P0172 (Fuel system too lean/too rich), DTC P0300/P0301 /P0302/P0303/P0304 (Misfire detected and DTC P0400 (EGR flow malfunction)
2. DTC P0171/P0172 (Fuel system too lean/too rich) and DTC P0400 (EGR flow malfunction)
3. DTC P0300/P0301 /P0302/P0303/P0304 (Misfire detected)

- Be sure to follow appropriate precautions for electrical system service.

- TCM and/or ECM replacement
When substituting a known-good TCM and/or ECM, check for the following conditions.
Neglecting this check may result in damage to a good TCM and/or ECM.
- All relays and actuators have resistance of specified value.
- MAF sensor, TP sensor and fuel tank pressure sensor (if equipped are in good condition. Also, the power circuit of these sensors is not shorted to the ground.