Mitsubishi Eclipse. Technical Information Manual (1994) — part 65
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A B S
INITIAL CHECK FUNCTION
The ECU always performs an initial check on the
ABS system with the on-board diagnostic function.
1. Initial Check Operation
(1) When the ignition key is placed in the ON posi-
tion, the power is supplied to the ABS-ECU,
and the ABS-ECU starts a diagnostic sequence.
During the diagnostic period, the ABS valve
relay stays in the “OFF” state and the warning
light continues to light.
If it detects an error, it illuminates the warning light,
and disables the ABS system.
(2) Then, the ABS-ECU forces the ABS valve relay
into the “ON” state and executes diagnostic test
mode of the ABS valve relay to detect an ON
or OFF failure.
(3) All the solenoid valves are caused to be ON
and OFF to make sure that the valves are not
sticking.
(4) With the ignition key placed in the “START”
position and engine started, the voltage at the
generator terminal L rises. At the moment, the
ABS-ECU power supply is cut off, but since
,
(3)
-
4
the ABS valve relay is caused to be “OFF”,
the warning light is kept in the ON state by
the ground contact circuit of the ABS valve relay.
(5) If the engine starts and the ignition key is re-
turned to the “ON” position, the ABS-ECU power
supply is resumed, and initial checks in (1)
through (3) are performed again.
(6) When the initial checks are satisfactorily com-
pleted, the ABS becomes ready for operation.
The warning light goes out upon detection of
a high voltage at the generator terminal L.
NOTE
An operation check for the motor relay and the motor
is performed when the vehicle is put in motion after
starting the engine. This check is performed only
one whenever the ignition switch is turned “ON”.
Ignition key
START
ON
ACC
ABS-ECU
power supply
. .
o v
Generator
terminal L
(Less than 6 V)
ABS warning
light
O
N
OFF
ABS valve
relay
ON
I
.
OFF
I
. . . . . .
Solenoid
valve
ON
OFF
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A B S
DIAGNOSIS OF THE WHEEL SPEED SENSOR SYSTEM
On-board diagnosis of the wheel speed sensor
is detectable only when the vehicle is put into
tern is accomplished by executing the diagnostic
motion or when it is running.
program stored in the computer. U&g the program,
the ABS-ECU monitors each wheel speed sensor
system (wheel speed sensor, rotor, etc.) to detect
a failure. In addition, the ABS-ECU monitors a short
or open circuit in the sensor system by using its
voltage monitoring circuit and voltage monitoring
program.
The former is called “software failure detection”,
whereas the latter is called “hardware failure detec-
tion”.
(1) Software failure detection
In this diagnostic test mode, the speeds of the
four wheels calculated from the sensor outputs
are compared. If there is any sensor system
that outputs an abnormal speed or an abnormal
decelerated speed, the ABS-ECU determines
that the system is out of order. Such a failure
FAIL-SAFE FUNCTION
Should a failure occur in the ABS system, the
ECU isolates the system to retain the vehicle’s ordi-
nary braking function, thus assuring a high measure
of safety.
l
If the ABS-ECU determines that the system
is defective as the result of diagnosis, it causes
DIAGNOSTIC FUNCTIONS
To facilitate inspection of the ABS system, the
ECU offers the following facilities:
l
Diagnostic trouble code output and erasure
l
Data list output
l
Actuator tests
All of the items described above can be checked
by the scan tool.
Scan Tool
ABS Interface
The scan tool function is entered by connecting
the scan tool to the data link connector. At this time,
(2) Hardware failure detection
The ABS-ECU monitors the sensors, harness,
etc. by using its open/short circuit monitoring
circuit and voltage monitoring program to detect
a failure such as an open or short circuit. A
major feature of the open/short circuit monitoring
circuit is that an open or short circuit failure
is always detectable (even when the vehicle
is stationary).
When the vehicle is in motion, however, a failure
may be detected by software failure detection
function before the same open or short circuit
failure is detected by the hardware failure detec-
tion function. Such a situation may occur de-
pending on the condition of vehicle and the
nature of the failure.
the ABS warning light to light, drives the valve
relay to interrupt control of the solenoid valves
in the HU, and restores the ordinary braking
mode.
the vehicle must be stopped, and the ignition should
be OFF.
The ABS scan tool mode is entered when you select
the ABS system on the scan tool. In this mode,
diagnostic output, data list output and actuator test
functions are available. During an actuator test, how-
ever, the ABS warning light illuminates and anti-lock
control is inhibited to prevent ABS operation when
a brake is temporarily inactivated during the actuator
test.
Scan tool
Wheel speeds of 0 km/h (0 mph), parked
mode entry
tion
condition
Check harness of scan tool connected to data
link connector of vehicle
ABS system selected by control switch of scan
tool (Specified serial data received)
NOTE
No communications with the ABS-ECU can be made by con-
necting the scan tool while the vehicle is in operation [wheel
speeds not 0 km/h (0 mph)]
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A B S
Diagnostic Trouble Codes
Conditions detected as a result of diagnosis are
associated with a total of 18 codes including that
These codes are readable by connecting the scan
,
for normal state, and the codes are stored in the
tool. When the scan tool is not used, they are also
volatile memory.
readable from the ABS warning light which is turned
Even if the ignition key is placed in the “OFF”
ON and OFF repeatedly in a pattern specific to
each code.
tion, the contents of the memory are not cleared,
as the memory remains powered by a backup power
1. Diagnostic items, diagnostic trouble codes and detection condition
Detection
Code No. display
on Scan tool
Inspection item
Diagnostic content
tions
A B
Front right wheel speed sensor
Front left wheel speed sensor
Open circuit or short in
x x
Rear right wheel speed sensor
Rear left wheel speed sensor
Wheel speed sensor system
Abnormal output signal
X
1
Power supply system
Abnormal battery positive voltage
x x
Front right wheel speed sensor
Front left wheel speed sensor
Excessive gap
Rear right wheel speed sensor
Long-time radio interference
X
Rear left wheel speed sensor
Stop light switch system
Open circuit or ON malfunction
x x
41
Front right solenoid valve
42
Front left solenoid valve
No response to solenoid valve drive
signal
43
Rear solenoid valve
51
Valve relay
Valve relay OFF failure
x x
Motor relay or Motor
Motor relay OFF failure and motor
drive failure
X
63
ABS-ECU
ABS-ECU internal failure (program
maze, etc)
No fault code
displayed
(The system is in order)
Detection conditions
A: During system check immediately after starting
B: During driving
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A B S
NOTE
The ABS-ECU can detect only an open circuit from the moment the ECU power supply is ON.
The ABS-ECU lights the ABS warning light when it detects an open circuit, but it does not immediately store
the trouble code in memory and does not cause the system to shut down.
When an open circuit is detected, the trouble code is stored in memory and the system caused to shut down
when the vehicle starts and the wheel speed reaches 6 km/h (4 mph) (the first acceleration after the
has
been placed in the ON state).
Troubles other than an open circuit cannot be detected until the wheel speed reaches 6 km/h (4 mph). When
the ABS-ECU detects any of these troubles, it causes the system to shut down and simultaneously lights the
ABS warning light.
When the ABS ECU detects a wheel speed sensor error during ABS control, it causes the system to shut down
and simultaneously lights the ABS warning light.
The ABS-ECU detects a power supply error when the supplied voltage is a low voltage (approx.
or less).
When the power supply error is detected, it causes the system to shut down and simultaneously lights the ABS
warning light, but does not store the trouble code in memory. The trouble code is stored in memory when the
voltage returns to normal.
When the power voltage is low (approx.
or less), none of the trouble codes is stored in memory.
The ABS-ECU takes more than 15 minutes from when it detects an error to when it determines that the fault
has occurred.
The ABS-ECU makes an initial check on the motor relay and motor when the wheel speed reaches 6 km/h
(4 mph) for the first time after engine start. If anything wrong is detected, it causes the system to shut down
and simultaneously lights the ABS warning light.
<Diagnostic Trouble Code Display by ABS Warning
(1) The codes for the currently present or previously
tic trouble
codes and goes back to the normal
occurred failures are displayed. Each code is
control mode. Thereafter, if the ABS system
displayed once. After all the codes in store have
is in order, the ABS control is available. If the
been displayed, they are repeatedly displayed,
system is out of order, the warning light
beginning with the first one.
nates and the brake system is placed in the
(2) If the vehicle is put in motion and any of the
ordinary braking mode. No more codes will be
wheels reaches a speed of more than
km/h
output until the ignition key is placed in the ON
(6 mph) during display of diagnostic trouble
position again.
codes, the system stops displaying the
2. Diagnostic Trouble Code Indication Method
Diagnostic trouble codes are indicated as described
below, depending on failure conditions in the system.
System failure condition
Display on scan tool
Display by ABS warning light
No failure detected in the past
No diagnostic trouble code displayed.
ON/OFF at 0.5 sec. intervals
(no-failure code)
detected in the past
All codes associated with the failures
All codes associated with the failures
that occurred in the past are displayed,
that occurred in the past are displayed,
beginning with the most recent one.
beginning with the most recent one.
NOTE
Even if failures of a same code repeatedly occur, the code that is displayed is the one stored for the first time only.
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