OBD - System Description
PURPOSEThe self-diagnostic system is designed to help technicians fix cars faster and with more accuracy. This is done by having ECCS Control Module (ECM) monitor certain input/outputs and store a trouble code if the ECM detects a problem.
OBD System Summary Chart:
RELATIONSHIP BETWEEN MIL, DTC, CONSULT, and DETECTABLE ITEMS
The ECCS control module has an on-board diagnostic system, which detects engine system malfunctions related to sensors or actuators. When a malfunction is detected for the first time, the DTC and the freeze frame data will be stored in ECM.
When the same malfunction is detected twice, malfunction indicator lamp (MIL) will automatically light up.
The MIL will go off automatically after 3 drivings without any malfunctions.
The DTC and the freeze frame data will not be displayed any longer after 40 drivings (except for Misfire, Fuel Injection System), 60 drivings (for Misfire, Fuel Injection System) without the same malfunction.
The "TIME" in "SELF-DIAGNOSTIC RESULTS" mode of CONSULT will be counted up in response to the number of drivings (pattern A or C) without the same malfunction.
TWO TRIP DETECTION LOGIC
When a malfunction is detected for the first time, the malfunction (DTC and freeze frame data) is stored in the ECM memory. <1st trip> The malfunction indicator lamp will not light up at this stage.
If the same malfunction is detected again during next drive, this second detection causes the malfunction indicator lamp to light up. <2nd trip>
The "trip" in the "Two Trip Detection Logic" means performing of the "DTC Detecting Condition". Only the following on-board diagnostic items will light up or blink the MIL even in the 1st trip.
^ Misfire (Criterion which will damage three way catalyst)" - DTC: 65-71 (P0304-P0300)
^ Three way catalyst function" - DTC: 72 (P0420)
ECM Update Priority Table:
FREEZE FRAME DATA
The ECM has a memory function, which stores the driving condition such as fuel system status, calculated load value, engine coolant temperature, short fuel trim, long fuel trim, engine speed, vehicle speed at the moment the ECM detects a malfunction.
Stored data is called Freeze Frame Data.
This data is useful for determining whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.
This data can be utilized to duplicate the malfunction and to diagnose the trouble.
This data will be erased at the same time with the diagnostic trouble code by the above mentioned methods.
The data can be stored only at the 1st trip. It can not be renewed even at the 2nd trip. The freeze frame data can be stored for only one item. Therefore, the ECM has the priorities, shown in the image, to update the data.
OBD System Operation Chart:
RELATIONSHIP BETWEEN MIL, DTC, CONSULT and DRIVING PATTERNS
*1: When the same malfunction is detected twice, MIL will automatically light up.
*2: MIL will go off automatically after 3 drivings (pattern B: except for "Misfire", "Fuel Injection System", pattern C: for "Misfire", "Fuel Injection System") without any malfunctions.
*3: When a malfunction is detected for the first time, the DTC and the freeze frame data will be stored in ECM.
*4:
(The DTC and the freeze frame data still remain in ECM.)
*5 Other screen except DATA MONITOR (AUTO TRIG) cannot display the malfunction.
*6: DATA MONITOR (AUTO TRIG) can display the malfunction at the moment it is detected.
*7: The malfunction can not be displayed because the timing to set DATA MONITOR (AUTO TRIG) screen was missed against the NG detection.
*8:
(The DTC and the freeze frame data still remain in ECM.)
Explanation For Driving Patterns Chart:
EXPLANATION OF DRIVING PATTERNS
Driving Pattern A (Except for "Misfire", "Fuel Injection System")
^ The A counter will be counted up when (1) - (4) are satisfied without the malfunction.
^ The A counter will be cleared when the malfunction is detected regardless of (1) - (4).
^ The DTC will not be displayed any longer after the A counter becomes 40.
Driving Pattern B
Driving pattern B means the vehicle operation as follows: All components and systems should be monitored at least once by the OBD system.
^ The B counter will be counted up when the driving pattern B is satisfied without the malfunction.
^ The B counter will be cleared when the malfunction is detected twice regardless of the driving pattern.
^ The MIL will go off when the B counter becomes 3. (Except for "Misfire", "Fuel Injection System".)
^ The DTC will not be displayed any longer after the B counter becomes 80. (For "Misfire", "Fuel Injection System".)
Driving pattern C (For "Misfire", "Fuel Injection System".)
Driving Pattern C means the vehicle operation as follows:
(1) Driving pattern A should be satisfied.
(2) The following condition should be satisfied:
Engine speed: (Engine speed in the freeze frame data) ±375 rpm Calculated load value: (Calculated load value in the freeze frame data) x (1 ±0.1) [%] Engine coolant temperature (T) condition: T > or = 70°C (158°F), T < 70°C (158°F)
Example:
If the stored freeze frame data is as follows:
Engine speed: 850 rpm, Calculated load value: 30%, Engine coolant temperature: 80°C (176°F) To be satisfied with driving pattern C, the vehicle should run under the following conditions:
Engine speed: 475 - 1,225 rpm, Calculated load value: 27 - 33%, Engine coolant temperature > or = 70°C (158°F)
^ The C counter will be counted up when (1), (2) are satisfied without the malfunction.
^ The C counter will be cleared when the malfunction is detected regardless of (1), (2).
^ The MIL will go off when the C counter becomes 3.