brake sensor SUBARU LEGACY 1995 Service Owner's Guide

1. Supplemental Restraint System
“Airbag”
Airbag system wiring harness is routed near the A.B.S.
control module, A.B.S. sensor and hydraulic control unit.
CAUTION:

All Airbag system wiring harness and connectors
are colored yellow. Do not use electrical test equip-
ment on these circuit.

Be careful not to damage Airbag system wiring har-
ness when servicing the A.B.S. control module, A.B.S.
sensor and hydraulic control unit.
2. Pre-inspection
Before performing diagnostics, check the following items
which might affect A.B.S. problems:
1. POWER SUPPLY
1) Measure battery voltage and specific gravity of electro-
lyte.
Standard voltage: 12 V, or more
Specific gravity: Above 1.260
2) Check the condition of the main and other fuses, and
harnesses and connectors. Also check for proper ground-
ing.
2. BRAKE FLUID
1) Check brake fluid level.
2) Check brake fluid leakage.
3. BRAKE DRAG
Check brake drag.
4. BRAKE PAD AND ROTOR
Check brake pad and rotor.
5. TIRE SPECIFICATIONS, TIRE WEAR AND AIR
PRESSURE
Check tire specifications, tire wear and air pressure. to 4-2 [S1A0].>
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1. Supplemental Restraint System“Airbag”- 2. Pre-inspection

3. Electrical Components Location
B4M0229A
1Hydraulic control unit

2G sensor (AWD MT model)

3A.B.S. control module

4Warning light
5Tone wheel

6A.B.S. sensor

7Diagnosis connector
G4M0766G4M0767G4M0917
B4M0574AG4M0769B4M0231A
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3. Electrical Components Location

4. Schematic
B4M0647A
1Hydraulic control unit

2Motor

3Motor relay

4Front left solenoid valve

5Front right solenoid valve

6Rear solenoid valve

7Valve relay

8AT control module

9A.B.S. control module

10Warning light
11Stop light

12Stop light switch

13G sensor (AWD MT model)

14Ignition switch

15Battery

16Front left sensor

17Front right sensor

18Rear left sensor

19Rear right sensor

20Diagnosis connector
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4. Schematic

5. Control Module I/O Signal
1. I/O SIGNAL VOLTAGE
G4M0685
ContentsTerminal
No.Ignition
switch ON,
engine
OFFInput/output signals
Measured value Measuring conditions
A.B.S.
sensorFront left wheel 22
0 V 0.12—1V
No. 22—No. 4
(When it is 10 Hz.)
GND 4
Front right wheel 23
0 V 0.12—1V
No. 23—No. 21
(When it is 10 Hz.)
GND 21
Rear left wheel 8
0 V 0.12—1V
No. 8—No. 9
(When it is 10 Hz.)
GND 9
Rear right wheel 24
0 V 0.12—1V
No. 24—No. 26
(When it is 10 Hz.)
GND 26
G sensor (AWD MT model) 13 10—12 V 0 V When slanting about 14°—21.3°(θ)
Diagnosis connector30
—— —
31
Stop light switch 25 0 V 10—12 V When brake pedal is depressed.
Motor monitoring 14 0 V 10—12 V When motor operates.
Valve power supply monitoring 32 10—12 V 10—12 V Ignition switch ON*1
Hydraulic
control
unitSolenoidFront left
wheel210—12 V 0 V
When solenoid is energized to
produce output. Front right
wheel35 10—12 V 0 V
Rear wheel 18 10—12 V 0 V
Valve relay coil 27 0 V 0 V Ignition switch ON*2
Motor relay coil 28 10—12 V 0 VWhen motor operates to produce
output.
Warning light 29 10—12 V 10—12 V Ignition switch ON*3
Power
supplyIgnition 1 10—12 V 10—12 V Ignition switch ON
Relay coil (valve,
motor, etc.)17 10—12 V 10—12 V Ignition switch ON
Grounding line10 0V 0V—
20 0V 0V—
34 0V 0V—
*1: When ignition switch is OFF or the A.B.S. system is inactive: 0 V
*2: When ignition switch is OFF or the A.B.S. system is inactive: 10—12 V
*3: When ignition switch is OFF or the A.B.S. system is inactive, or during 1.5 seconds from ignition switch ON: 0 V
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5. Control Module I/O Signal

7. Diagnostics Chart with Trouble Code
Trouble code Contents of diagnosis Ref. to 4-4a
NONE: A
[Warning light OFF]Trouble in warning light drive circuit
(Warning light is not on for 1.5 seconds after ignition switch is on.)[T7A0]
NONE: B
[Warning light ON] or
[Abnormal trouble code output]Trouble in warning light drive circuit [T7B0]
11Start code:

Trouble code is shown after start code.

Only start code is shown in normal condition.—
21
Faulty A.B.S. sensor
(Open circuit or input voltage
excessive)Front right wheel sensor [T7C0]
23 Front left wheel sensor [T7C0]
25 Rear right wheel sensor [T7C0]
27 Rear left wheel sensor [T7C0]
22
Faulty A.B.S. sensor
(When there is no open circuit or
speed signal input.)Front right wheel sensor [T7D0]
24 Front left wheel sensor [T7D0]
26 Rear right wheel sensor [T7D0]
28 Rear left wheel sensor [T7D0]
29 Faulty tone wheel, etc. [T7E0]
31
Faulty solenoid valve circuit(s) in
hydraulic control unitFront right wheel control [T7F0]
33 Front left wheel control [T7F0]
39 Rear wheels control [T7F0]
41 Faulty A.B.S. control module [T7G0]
42 Source voltage is low. [T7H0]
51 Faulty valve relay [T7I0]
52 Faulty hydraulic motor and/or motor relay [T7J0]
54 Faulty stop light circuit [T7K0]
56 Use of improper A.B.S. control module specification, or faulty G sensor [T7L0]
NOTE:
After diagnostics is completed, make sure to clear memory.
Make sure only start code (11) is shown after memory is
cleared.
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7. Diagnostics Chart with Trouble Code

C: TROUBLE CODE 21, 23, 25 AND 27
—FAULTY A.B.S. SENSOR (OPEN CIRCUIT
OR INPUT VOLTAGE EXCESSIVE)—
DIAGNOSIS:

Faulty A.B.S. sensor

Faulty harness

Faulty A.B.S. control module
TROUBLE SYMPTOM:

A.B.S. does not operate.
NOTE:
Trouble codes 21, 23, 25, and 27 will not be stored while
vehicle is stationary and can’t specify problem location.
Drive vehicle first, perform diagnosis and read trouble
code.
1. Check resistance of A.B.S. sensor to
A.B.S. control module side.
OK
Not OK
4. Check resistance of A.B.S. sensor.
Not OK OK
Replace A.B.S. sensor.
Repair harness/connector.
2. Check input signal of A.B.S. sensor to
A.B.S. control module side.
Not OK
OK
Replace A.B.S. control module.
3. Check A.B.S. sensor mechanical trouble.
OK
Not OK
Repair mechanical trouble.
Replace A.B.S. sensor.
NOTE:
When checking A.B.S. sensor, carefully bend or swing con-
nector and harness to check for improper contacts or open
circuits.





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7. Diagnostics Chart with Trouble Code

B4M0583
B4M0584A
1. CHECK RESISTANCE OF A.B.S. SENSOR TO
A.B.S. CONTROL MODULE SIDE.
1) Turn ignition switch OFF.
2) Disconnect connector from A.B.S. control module.
3) Measure resistance between A.B.S. control module
connector terminals.
TROUBLE CODE / Connector & terminal:
21 / (P3) No. 23—No. 21
23 / (P3) No. 22—No. 4
25 / (P3) No. 24—No. 26
27 / (P3) No. 8—No. 9
Specified resistance: 0.8—1.2 kΩ
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7. Diagnostics Chart with Trouble Code

B4M0585A
4) Measure resistance between A.B.S. control module
connector and body.
TROUBLE CODE / Connector & terminal:
21 / (P3) No. 23—body
23 / (P3) No. 22—body
25 / (P3) No. 24—body
27 / (P3) No. 8—body
Specified resistance: 1 MΩ, min.
B4M0586A
5) Turn ignition switch ON.
6) Measure voltage between A.B.S. control module con-
nector and body.
TROUBLE CODE / Connector & terminal:
21 / (P3) No. 23—body
23 / (P3) No. 22—body
25 / (P3) No. 24—body
27 / (P3) No. 8—body
Specified voltage: 0 V
G4M0698
2. CHECK INPUT SIGNAL OF A.B.S. SENSOR TO
A.B.S. CONTROL MODULE SIDE.
1) Raise all four wheels of ground.
2) Turn ignition switch OFF.
3) Disconnect connector from A.B.S. control module.
4) Disconnect connector cover from connector.
(a) Remove screw from portion
1.
(b) Move rubber boot
2back (toward harness).
(c) Slide cover
3in direction shown by arrow and
remove.
5) Connect connector to A.B.S. control module.
6) Connect the oscilloscope to the A.B.S. control module
connector in accordance with trouble code.
7) Turn ignition switch ON.
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7. Diagnostics Chart with Trouble Code

B4M0711A
8) Rotate wheels and measure voltage at specified fre-
quency.
NOTE:
When this inspection is completed, the A.B.S. control mod-
ule sometimes stores the trouble code 29.
TROUBLE CODE / Connector & terminal:
21 / (P3) No. 23 (+)—No. 21 ()
23 / (P3) No. 22 (+) — No. 4 ()
25 / (P3) No. 24 (+) — No. 26 ()
27 / (P3) No. 8 (+) — No. 9 ()
Specified voltage: 0.12 — 1 V (When it is 20 Hz.)
G4M0700
G4M0701
3. CHECK A.B.S. SENSOR MECHANICAL TROUBLE.
1) Dismount brake as outlined in manual to gain access to
A.B.S. sensor and tone wheel for inspection.
2) Check pole piece and tone wheel for accumulation of
foreign particles. If necessary, remove foreign particles and
clean.
3) Check tone wheel teeth for cracks for deformities. If
necessary, replace tone wheel (No. of teeth: 44) with a new
one.
4) Check tone wheel for looseness.
Tightening torque:
10 — 16 N⋅m (1.0 — 1.6 kg-m, 7 — 12 ft-lb)
5) Measure tone wheel-to-pole piece gap over entire
perimeter of the wheel.
SpecificationsFront wheel Rear wheel
0.9—1.4 mm
(0.035—0.055 in)0.7—1.2 mm
(0.028—0.047 in)
If measurements check out“Not OK”, adjust the gap using
spacers (Part No. 26755AA000). If spacers cannot correct
the gap, replace worn sensor or worn tone wheel.
6) Check hub runout.
Specifications 0.05 mm (0.0020 in)
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7. Diagnostics Chart with Trouble Code

B4M0248B
4. CHECK RESISTANCE OF A.B.S. SENSOR.
1) Turn ignition switch OFF.
2) Disconnect connector from A.B.S. sensor.
3) Measure resistance between A.B.S. sensor connector
terminals.
TROUBLE CODE / Connector & terminal:
21 / (B6) No. 1—No. 2
23 / (B15) No. 1—No. 2
25 / (P8) No. 1—No. 2
27 / (P9) No. 1—No. 2
Specified resistance: 0.8—1.2 kΩ
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7. Diagnostics Chart with Trouble Code