The engine ECU possesses an OBD (On-Board Diagnostic) function which constantly monitors each sensor and actuator. If it detects a malfunction, the malfunction is recorded as a DTC (Diagnostic Trouble Code) and the MIL (Malfunction Indicator Lamp) on the combination meter lights up to inform the driver. By connecting the hand-held tester to DLC3, direct communication with the engine ECU can be performed via terminal SIL to confirm the DTC. The DTC can also be confirmed by causing the MIL to blink, then checking the blinking pattern.
HINT: The MIL may also be called the CHECK ENGINE warning light or engine system warning light.
Type of OBD
To confirm the DTC or data recorded by the engine ECU, a diagnosis system called MOBD, CARB OBD II, EURO OBD or ENHANCED OBD II is used to communicate directly with the engine ECU. Each of these systems displays a 5-digit DTC on the hand-held tester.
1. MOBD
The MOBD is diagnosis system unique to Toyota. It can be used to check the DTC or data for ToyotaÅfs own items.
2. CARB OBD II
The CARB OBD II is an emission diagnostic system used in the USA and Canada. It is used to check the DTC or data for items required by US and Canadian regulations.
3. EURO OBD
The EURO OBD is an emission diagnostic system used in Europe. It is used to check the DTC or data for items required by European regulations.
4. ENHANCED OBD II
The ENHANCED OBD II is a diagnostic system used in the USA and Canada. It is used to check items required by US and Canadian regulations, and check the DTC or data for ToyotaÅfs own items.
HINT: The earlier type of OBD used the MIL blinking pattern to check the DTC. The system read the data output by the engine ECU without communicating with the engine ECU.
Principal of Diagnosis
The engine ECU receives signals from the sensors in the form of voltage. The engine ECU can determine the conditions of the engine or the vehicle running by detecting the changes in the voltage of the signals that are output by the sensors. Thus, the engine ECU constantly monitors the input signals (voltage), compares them to the reference values that are stored in the engine ECU’s memory, and determines any abnormal conditions. The graph on the left shows the characteristics of a water temperature sensor. Normally, the voltage of the water temperature sensor should vary between 0.1V and 4.8V. When a voltage within this range is input, the engine ECU determines that the condition is normal. If short (the input voltage is less than 0.1 V) or broken wire (the input voltage is more than 4.8 V) occurs, it determines abnormal. However, even if the range of 0.1V to 4.8V is normal for diagnostic purposes, it may indicate a malfunction depending on the engine condition. The monitoring conditions of the DTC from the engine ECU differ according to the DTC, such as the requirement of driving, changes in the coolant temperature, etc., so refer to the Repair Manual for details
Function of MIL
The MIL has the following functions.
1. Lamp check function (engine stopped)
The MIL is turned on when the ignition switch is turned to ON, and it turns off when the engine speed reaches 400 rpm or more, to check whether the bulb is functioning or not.
2. Malfunction indicator function (engine running)
If the engine ECU detects a malfunction in a circuit, the engine ECU is monitoring while the engine is running, it turns on the MIL to inform the driver of a malfunction. When the malfunction has returned to normal, the lamp goes off after 5 seconds. For CARB OBD II and EURO OBD, when a malfunction returns to normal, the MIL turns off if no malfunction is detected in three continuous driving cycles.
HINT:
DTCs include some items where the DTC is stored in the engine ECU by detecting a malfunction, but the MIL does not turn on.
3. Diagnostic code display function
When shorted the terminals TE1-E1 on vehicles equipped with only DLC1 and DLC2, the DTC is displayed by the MIL blinking pattern. On vehicles equipped with DLC3, when shorted the terminals TC-CG, there are systems where the DTC is displayed by the MIL blinking pattern, and systems where the MIL does not blink.
1. MIL-ON one driving cycle detection
If a malfunction is detected during one driving cycle, the engine ECU turns the MIL on. The DTC and freeze frame data are simultaneously stored in the engine ECU when the MIL turns on.
HINT:
The freeze frame data is input/output signal data stored in the engine ECU when the DTC is detected.
2. MIL-ON two driving cycle detection
If the same malfunction is detected during two continuous driving cycle, the engine ECU turns the MIL on at two driving cycle. When the MIL turns on, the DTC and freeze frame data are simultaneously stored in the engine ECU. In this case, the malfunction that is detected at one driving cycle is stored as the pending code in the engine ECU. However the pending code is cleared if the same malfunction is not detected at two driving cycle. The function is activated when a malfunction occurs mainly in the emission system.
3. MIL blinking
If a misfire that may damage the catalytic converter is detected in the first driving cycle, the MIL blinks. If the same misfire is detected in the second driving cycle, the MIL blinks, and the DTC and freeze frame data are recorded in the engine ECU memory. If the misfire symptoms decline, the MIL changes from blinking to continuous illumination. *Driving cycle: One driving cycle refers to the period from when the engine is started until the engine is stopped.