Suzuki Engine 2002 GRAND VITARA SQ625, Service Manual

Page: 149 / 834

6-1-8 ENGINE GENERAL INFORMATION AND DIAGNOSIS (H25 ENGINE)
Engine Diagnosis
General Description
This vehicle is equipped with an engine and emission control system which are under control of ECM (PCM).
The engine and emission control system in this vehicle are controlled by ECM (PCM). ECM (PCM) has an On-
Board Diagnostic system which detects a malfunction in this system and abnormality of those parts that influ-
ence the engine exhaust emission. When diagnosing engine troubles, be sure to have full understanding of the
outline of “On-Board Diagnostic System” and each item in “Precaution in Diagnosing Trouble” and execute diag-
nosis according to “Engine Diagnostic Flow Table” in this section.
There is a close relationship between the engine mechanical, engine cooling system, ignition system, exhaust
system, etc. and the engine and emission control system in their structure and operation. In case of an engine
trouble, even when the malfunction indicator lamp (MIL) doesn’t turn ON, it should be diagnosed according to
“Engine Diagnostic Flow Table” in this section.
On-Board Diagnostic System (Vehicle without
Diagnosis Connector)
ECM (PCM) in this vehicle has following functions.
• When the ignition switch is turned ON with the engine at a
stop, MIL (1) turns ON to check the circuit of the malfunction
indicator lamp (MIL).
• When ECM (PCM) detects a malfunction which gives an
adverse effect to vehicle emission while the engine is run-
ning, it makes the malfunction indicator lamp 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 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 (PCM) and turning ON
the malfunction indicator lamp due to that malfunction, 2
driving cycle detection logic is adopted to prevent erroneous
detection.
• When a malfunction is detected, engine and driving condi-
tions then are stored in ECM (PCM) 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 generic scan tool. (Diagnostic information
can be accessed by using a scan tool.)
or
2
1