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.
Section 598 (Electronic Controlled Automatic Transmission (ECT) - Diagnosis): Pre-Check
- DIAGNOSIS SYSTEM
- Description
- When troubleshooting vehicles with OBD II, the only difference from the usual troubleshooting procedure is that you connect an OBD II scan tool complying with SAE J1987 or LEXUS handheld tester to the vehicle, and read off various data output from the vehicle's ECM.
- OBD II regulations require that the vehicle's on board computer lights up the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in the computer itself or in drive system components which affect vehicle emissions. In addition to the MIL lighting up when a malfunction is detected, the applicable DTCs prescribed by SAE J2012 are recorded in the ECM memory (See
FUEL SYSTEM
).
If the malfunction only occurs in 3-trips, the MIL goes off but the DTCs remain recorded in the ECM memory.
- To check the DTCs, connect an OBD II scan tool or LEXUS hand held tester to DLC3 on the vehicle. The OBD II scan tool or LEXUS hand held tester also enables you to erase the DTCs and check freeze frame data and various forms of engine data (For instruction book).
- DTCs include SAE controlled codes and Manufacturer controlled codes.
SAE controlled codes must be set as the codes prescribed by the SAE, while Manufacturer controlled codes can be set freely by the manufacturer within the prescribed limits (See DIAGNOSTIC TROUBLE CODE CHART ).
- The diagnosis system operates in normal mode during normal vehicle use, and also has a check mode for technicians to simulate malfunction symptoms and perform troubleshooting. Most DTCs use 2-trip detection logic (*) to prevent erroneous detection. By switching the ECM to check mode when troubleshooting, the technician can cause the MIL to light up for a malfunction that is only detected once or momentarily (LEXUS hand held tester) (See FUEL SYSTEM ).
- *2-trip detection logic:
When a logic malfunction is first detected, the malfunction is temporarily stored in the ECM memory. If the same malfunction is detected again during the 2nd test drive, this 2nd detection causes the MIL to light up. The 2-trip repeats the same mode 2nd time (However, the IG switch must be turned OFF between the 1st trip and 2nd trip.).
- Inspect the DLC3.
The vehicle's ECM uses the ISO 9141-2 communication protocol. The terminal arrangement of DLC3 complies with SAE J1962 and matches the ISO 9141-2 format.
DLC3 TERMINALS VOLTAGE /RESISTANCE AND CONDITION SPECIFICATIONSTerminal No. Connection / Voltage or Resistance Condition 7 Bus (+) Line / Pulse generation During communication 4 Chassis Ground <-> Body / 1 Ω or less Always 5 Signal Ground <-> Body / 1 Ω or less Always 16 Battery Positive <-> Body / 9 - 14 V Always NOTE: If your display shows "UNABLE TO CONNECT TO VEHICLE" when you have connected the cable of OBD II scan tool or LEXUS hand held tester to DLC3, turned the ignition switch ON and operated the scan tool, there is a problem on the vehicle side or tool side.- If communication is normal when the tool is connected to another vehicle, inspect DLC3 on the original vehicle.
- If communication is still not possible when the tool is connected to another vehicle, the problem is probably in the tool itself, so consult the Service Department listed in the tool's instruction manual.
- Description
- INSPECT DIAGNOSIS (NORMAL MODE)
- Check the MIL.
- The MIL comes on when the ignition switch is turned ON and the engine is not running.NOTE: If the MIL does not light up, troubleshoot the combination meter (See INDICATORS AND WARNING LIGHT DOES NOT LIGHT UP ).
- When the engine is started, the MIL should go off. If the lamp remains on, the diagnosis system has detected a malfunction or abnormality in the system.
- The MIL comes on when the ignition switch is turned ON and the engine is not running.
- Check the DTC.NOTE: LEXUS hand held tester only: When the diagnostic system is switched from normal mode to check mode, it erases all DTCs and freeze frame data recorded in normal mode. So before switching modes, always check the DTCs and freeze frame data, and note them down.
- Prepare an OBD II scan tool (complying with SAE J1978) or LEXUS hand held tester.
- Connect the OBD II scan tool or LEXUS hand held tester to DLC3 at the lower of the instrument panel.
- Turn the ignition switch ON and turn the OBD II scan tool or LEXUS hand held tester switch ON.
- Use the OBD II scan tool or LEXUS hand held tester to check the DTCs and freeze frame data and note them down (For operating instructions, see the OBD II scan tool's instruction book).
- See DIAGNOSTIC TROUBLE CODE CHART to confirm the details of the DTCs.
NOTE: When simulating symptoms with an OBD II scan tool (excluding LEXUS hand held tester) to check the DTCs, use normal mode. For codes on the DTCs chart subject to "2-trip detection logic", tun the ignition switch OFF after the symptoms have been simulated the 1st time. Then repeat the simulation process again. When the program has DTCs, the DTCs are recorded in the ECM. - Check the MIL.
- INSPECT DIAGNOSIS (CHECK MODE) NOTE: LEXUS hand held tester only: Compared to the normal mode, the check mode has high sensing ability to detect malfunctions. Furthermore, the same diagnostic items which are detected in Normal mode can also be detected in Check mode.
- Check the DTC.
- Check the initial conditions.
- Battery positive voltage 11 V or more
- Throttle valve fully closed
- Transmission in P position
- Air conditioning switched OFF
- Turn the ignition switch OFF.
- Prepare a LEXUS hand held tester.
- Connect the LEXUS hand held tester to DLC3 at the lower side of the instrument panel.
- Turn the ignition switch ON and switch the LEXUS hand held tester ON.
- Switch the LEXUS hand held tester from Normal mode to Check mode (Check that the MIL flashes).
- Start the engine (MIL goes out after the engine starts).
- Simulate the conditions of the malfunction described by the customer.NOTE: Leave the ignition, switch ON until you have checked the DTCs, etc.
- After simulating the malfunction conditions, use the LEXUS hand held tester diagnosis selector to check the DTCs and freeze frame data, etc.
- Check the initial conditions.
- Check the DTC.
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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.