Description of On-Board Diagnostics
DIAGNOSTIC SYSTEM DESCRIPTIONTOYOTA COMPUTER CONTROL SYSTEM (TCCS) Part 1 Of 2:
TOYOTA COMPUTER CONTROL SYSTEM (TCCS) Part 2 Of 2:
The ECM contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a Malfunction Indicator Lamp (MIL) on the instrument panel lights up. By analyzing various signals as shown in the later table the Engine Control Module (ECM) detects system malfunctions relating to the sensors or actuators.
In the normal mode, the self-diagnosis system monitors 15 (for vehicles with A/T), or 14 (for M/T) items, indicated by code numbers. A Malfunction Indicator Lamp informs the driver that a malfunction has been detected. The lamp goes OFF automatically when the malfunction has been repaired, but the diagnostic trouble code(s) remains stored in the ECM memory (except for code No.16). The ECM stores the code(s) unit it is cleared by removing the "EFI" fuse with the ignition switch OFF.
The diagnostic trouble code can be read by the number of blinks of the Malfunction Indicator Lamp when TE1 and E1 terminals on the data link connector 1 (DLC1) are connected. When 2 or more codes are indicated, the lowest number (code) will appear first.
In the test mode, 10 items, indicated by code No. are monitored. If a malfunction is detected in any one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26, 27, 31, 41 and 71 the ECM lights the Malfunction Indicator Lamp to warn the technician that malfunction has been detected. In this case, TE2 and E1 terminals of DLC1 should be connected to initiate the test mode.
In the test mode as well as the normal mode, even if the malfunction is corrected, the malfunction code is stored in the ECM memory even when the ignition switch is OFF (Except code Nos. 43 and 51).
The test mode function has been added to the functions of the self-diagnosis system for the purpose of detecting intermittent malfunctions, such as poor contact, which are difficult to detect in the normal mode.
MALFUNCTION INDICATOR LAMP (MIL) - ("CHECK" ENGINE LIGHT)
1. The malfunction indicator lamp will come ON when the ignition switch is placed at ON and the engine is NOT RUNNING.
2. When the engine is started, the MIL should go OFF.
^ If the light remains ON, the diagnosis system has detected a malfunction or abnormality in the system.
2 TRIP DETECTION LOGIC
Certain data trouble codes (DTC) (21, 25, 26, 27 and 71), can be triggered by driving conditions without a malfunction present. To improve self diagnostic reliability, "2nd trip" detect logic is used.
When any a fault related to any of the above DTC's is detected, the ECM retains a temporary record of the fault in memory. An actual code is set only if the same fault is recorded during the next ignition/driving cycle.
The MIL is only illuminated after the "2nd trip".
Because the ECM must see the fault for 2 consecutive trips, the chances of a false code are greatly reduced.
A specific driving pattern must be followed to recreate a fault code that employs 2 trip detection logic.
Two Trip Detection Logic - Driving Pattern:
^ Drive the vehicle in the same manner the customer has indicated caused the fault.
^ Stop vehicle and turn ignition OFF.
^ Restart vehicle and repeat test-drive.
BACK-UP FUNCTION (FAIL-SAFE MODE)
Fail-Safe Chart:
If there is trouble with the program in the ECM and the ignition signals (IGT) are not output from microcomputer, the ECM controls fuel injection and ignition timing at predetermined levels as a back-up function to make it possible to continue to operate the vehicle.
Furthermore, the injection duration is calculated from the starting signal (STA) and the throttle position signal (IDL). Also, the ignition timing is fixed at the initial ignition timing, 5° BTDC, without relation to the engine speed.
HINT: If the engine is controlled by the back-up function, the malfunction indicator lamp lights up to warn the driver of the malfunction but the diagnostic trouble code is not output.
VERIFICATION OF REPAIR
After repairs, clear ECM memory and follow the same driving pattern used for code detection. If the same trouble code(s) is displayed, the problem has not been thoroughly repaired.