On-Board Diagnostic System Description
ECM in this vehicle has the following functions.
When the ignition switch is turned ON with the engine at a stop, malfunction indicator lamp (MIL) (1) turns ON to check the circuit of the malfunction indicator lamp (1).
When ECM detects a malfunction which gives an adverse effect to vehicle emission while the engine is running, it makes the malfunction indicator lamp (1) in the meter cluster of the instrument panel turn ON or flash (flashing only when detecting a misfire which can cause damage to the catalyst) and stores the malfunction area in its memory.
(If it detects that continuously 3 driving cycles are normal after detecting a malfunction, however, it makes MIL (1) turn OFF although DTC stored in its memory will remain.)
As a condition for detecting a malfunction in some areas in the system being monitored by ECM and turning ON the malfunction indicator lamp (1) due to that malfunction, 2 driving cycle detection logic is adopted to prevent erroneous detection.
When a malfunction is detected, engine and driving conditions then are stored in ECM memory as freeze frame data. (For the details, refer to description on Freeze Frame Data .)
It is possible to communicate by using not only SUZUKI scan tool (2) but also OBD generic scan tool. (Diagnostic information can be accessed by using a scan tool.)
Warm-Up Cycle
A warm-up cycle means sufficient vehicle operation such that the coolant temperature has risen by at least 22 °C (40 °F) from engine starting and reaches a minimum temperature of 70 °C (160 °F).
Driving Cycle
A “Driving Cycle” consists of engine startup, driving mode where a malfunction would be detected if present and engine shutoff.
2 Driving Cycles Detection Logic
The malfunction detected in the first driving cycle is stored in ECM memory (in the form of pending DTC and freeze frame data) but the malfunction indicator lamp does not light at this time. It lights up at the second detection of same malfunction also in the next driving cycle.
Pending DTC
Pending DTC means a DTC detected and stored temporarily at 1 driving cycle of the DTC which is detected in the 2 driving cycle detection logic.
Freeze Frame Data
ECM stores the engine and driving conditions (in the form of data as shown in the figure) at the moment of the detection of a malfunction in its memory. This data is called “Freeze frame data”.
Therefore, it is possible to know engine and driving conditions (e.g., whether the engine was warm or not, where the vehicle was running or stopped, where air/fuel mixture was lean or rich) when a malfunction was detected by checking the freeze frame data. Also, ECM has a function to store each freeze frame data for three different malfunctions in the order as the malfunction is detected. Utilizing this function, it is possible to know the order of malfunctions that have been detected. Its use is helpful when rechecking or diagnosing a trouble.
[A]: An example of freeze frame data.
[B]: 1st, 2nd or 3rd in parentheses here represents which position in the order the malfunction is detected.
Priority of freeze frame data:
ECM has 4 frames where the freeze frame data can be stored. The first frame stores the freeze frame data of the malfunction which was detected first. However, the freeze frame data stored in this frame is updated according to the priority described. (If malfunction as described in the upper square “1” is detected while the freeze frame data in the lower square “2” has been stored, the freeze frame data “2” will be updated by the freeze frame data “1”.)
Priority Freeze frame data in frame 1
1 Freeze frame data at initial detection of malfunction among misfire detected (P0300 – P0304), fuel system too lean (P0171) and fuel system too rich (P0172)
2 Freeze frame data when a malfunction other than those in “1” above is detected
In the 2nd through the 4th frames, the freeze frame data of each malfunction is stored in the order as each malfunction is detected. These data are not updated.
Shown in the table are examples of how freeze frame data are stored when two or more malfunctions are detected.
Malfunction detected order Frame
Frame 1 Frame 2 Frame 3 Frame 4
Freeze frame data to be updated 1st freeze frame data 2nd freeze frame data 3rd freeze frame data
   No malfunction No freeze frame data
1 P0401 (EGR)
Data at P0401 detection Data at P0401 detection
2 P0171 (Fuel system)
Data at P0171 detection Data at P0401 detection Data at P0171 detection
3 P0300 (Misfire)
Data at P0171 detection Data at P0401 detection Data at P0171 detection Data at P0300 detection
4 P0301 (Misfire)
Data at P0171 detection Data at P0401 detection Data at P0171 detection Data at P0300 detection
Freeze frame data clearance:
The freeze frame data is cleared at the same time as clearance of diagnostic trouble code (DTC).
Data Link Connector (DLC)
DLC (1) is in compliance with SAE J1962 in the shape of connector and pin assignment.
OBD serial data line (3) (K line of ISO 9141) is used for SUZUKI scan tool or OBD generic scan tool to communicate with ECM, TCM, Air bag SDM and ABS control module.
SUZUKI serial data line (6) is used for SUZUKI scan tool to communicate with immobilizer control module.
2. B + 4. ECM ground 5. Body ground