Diagnosis System

When troubleshooting On-Board Diagnostic (OBD II) vehicles, the vehicle must be connected to the OBD II scan tool (complying with SAE J1987). Various data output from the vehicle's ECM can then be read.

• OBD II regulations require that the vehicle's on-board computer illuminates the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in:
  1. The emission control system/components
  2. The powertrain control components (which affect vehicle emissions)
  3. The computer

  In addition, the applicable Diagnostic Trouble Codes (DTCs) prescribed by SAE J2012 are recorded in the ECM memory.

  If the malfunction does not reoccur in 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the ECM memory.

  Fig 1: Identifying MIL

  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
• To check DTCs, connect the hand-held tester to the Data Link Connector 3 (DLC3) of the vehicle. The hand-held tester displays DTCs, the freeze frame data and a variety of the engine data.
  1. The DTCs and freeze frame data can be erased with the hand-held tester (See DTC CHECK/CLEAR  ).

Fig 2: Connecting Hand-Held Tester To DLC3

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

The diagnosis system operates in "normal mode" during normal vehicle use. In normal mode, "2-trip detection logic" is used to ensure accurate detection of malfunctions. "Check mode" is also available to technicians as an option. In check mode, "1-trip detection logic" is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent malfunctions.

When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). If the ignition switch is turned OFF and then ON again, and the same malfunction is detected again, the MIL will illuminate.

• Freeze frame data records the engine conditions (fuel system, calculated load, engine coolant temperature, fuel trim, engine speed, vehicle speed, etc.) when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air/fuel ratio was Lean or Rich, and other data from the time the malfunction occurred.
• The hand-held tester records freeze frame data in five different instances: 1) 3 times before the DTC is set, 2) once when the DTC is set, and 3) once after the DTC is set. These data can be used to simulate the vehicle's condition around the time when the malfunction occurred. The data may help find the cause of the malfunction, or judge if the DTC is being caused by a temporary malfunction or not.

Fig 3: Identifying Freeze Frame Data

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

• The vehicle's ECM uses the ISO 15765-4 communication protocol. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.

HINT:

Connect the cable of the hand-held tester (with CAN VIM) or OBD II scan tool to the DLC3, turn the ignition switch ON and attempt to use the hand-held tester. If the screen displays UNABLE TO CONNECT TO VEHICLE, a problem exists in the vehicle side or the tester side.

If communication is normal when the tester is connected to another vehicle, inspect the DLC3 on the original vehicle. If communication is still not possible when the tester is connected to another vehicle, the problem is probably in the tester itself. Consult the Service Department listed in the tester's instruction manual.

Fig 4: Identifying DLC3 Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Standard: 11 to 14 V 

If voltage is below 11 V, replace the battery before proceeding.

1. Check that the MIL illuminates when turning the ignition switch ON.

   If the MIL does not illuminate, there is a problem in the MIL circuit (refer to MIL CIRCUIT  ).

2. When the engine is started, the MIL should turn off.

For this vehicle, using the hand-held tester allows readiness codes corresponding to all DTCs to be read. When diagnosis (normal or malfunctioning) has been complete, readiness codes are set. Enter the following menus: ENHANCED OBD II / MONITOR STATUS on the hand-held tester.