Subaru 2009 IMPREZA Service Manual page 1227

ENGINE (DIAGNOSTICS)
11) When disconnecting the fuel hose, release the
fuel pressure. <Ref. to FU(H4DOTC)-60, RELEAS-
ING OF FUEL PRESSURE, PROCEDURE, Fuel.>
12) Warning lights may illuminate when performing
driving test with jacked-up or lifted-up condition, but
this is not a system malfunction. The reason for this
is the speed difference between the front and rear
wheels. After diagnosis of engine control system,
perform the ABS memory clear procedure of self-
diagnosis function.
B: INSPECTION
Before performing diagnostics, check the following
item which might affect engine problems.
1. BATTERY
1) Measure the battery voltage and specific gravity
of the electrolyte.
Standard voltage: 12 V
Specific gravity: 1.260 or more
2) Check the condition of the main and other fuses,
and harnesses and connectors. Also check for
proper grounding.
2. ENGINE GROUND
Check if the engine ground terminal is properly
connected to engine.
General Description
C: NOTE
• The on-board diagnostic (OBD) system detects
and indicates a fault in various inputs and outputs
of the complex electronic control. Malfunction indi-
cator light in the combination meter indicates oc-
currence of a fault or trouble.
• Further, against such a failure of sensors as may
disable the drive, the fail-safe function is provided
to ensure the minimal drivability.
• The OBD system incorporated with the vehicles
within this type of engine complies with OBD-II reg-
ulations. The OBD system monitors the compo-
nents and the system malfunction listed in "Engine
Section" which affects on emissions.
• When the system decides that a malfunction oc-
curs, malfunction indicator light illuminates. At the
same time of the malfunction indicator light illumi-
nation or blinking, a DTC and a freeze frame en-
gine conditions are stored into on-board computer.
• The OBD system stores freeze frame engine
condition data (engine load, engine coolant tem-
perature, fuel trim, engine speed and vehicle
speed, etc.) into on-board computer when it detects
a malfunction.
• Freeze frame engine condition data are stored
until the DTCs are cleared. However when such
malfunctions as fuel trim fault and misfire are de-
tected with the freeze frame engine condition data
stored, they are rewritten into those related to the
fuel trim fault and misfire.
• When the malfunction does not occur again for
three consecutive driving cycles, malfunction indi-
cator light is turned off, but DTC remains at on-
board computer.
• When performing diagnosis, connect the Subaru
Select Monitor or general scan tool to the vehicle.
FU-01170
EN(H4DOTC)(diag)-6