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Mitsubishi Eclipse. Technical Information Manual (1994) - part 65

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)

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

ACC

ABS-ECU

power supply

. .

o v

Generator

terminal L

(Less than 6 V)

ABS warning

light

OFF

ABS valve
relay

OFF

. . . . . .

Solenoid

valve

OFF

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.

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:

Diagnostic trouble code output and erasure

Data list output

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)]

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

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

Rear left wheel speed sensor

Stop light switch system

Open circuit or ON malfunction

x x

Front right solenoid valve

Front left solenoid valve

No response to solenoid valve drive
signal

Rear solenoid valve

Valve relay

Valve relay OFF failure

x x

Motor relay or Motor

Motor relay OFF failure and motor
drive failure

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

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

that occurred in the past are displayed,

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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