1997 SUBARU LEGACY ABS

B: TROUBLE CODE 21, 23, 25 AND 27
—FAULTY ABS SENSOR (OPEN CIRCUIT OR
SHORT CIRCUIT)—
DIAGNOSIS:

Faulty ABS sensor

Faulty harness/connector

Faulty ABS/TCS control module
TROUBLE SYMPTOM:

ABS does not operate.

TCS does not operate.
1. Check resistance of ABS sensor.
OK
Not OK
Replace ABS sensor.
2. Check body short of ABS sensor.
OK
Not OK
Replace ABS sensor.
3. Check harness connector between ABS/TCS
control module and ABS sensor.
OK
Not OK
Repair harness/connector.
4. Check body short of harness.
OK
Not OK
Repair harness/connector.
Replace ABS/TCS control module.
NOTE:
When checking ABS sensor, carefully bend or swing con-
nector and harness to check for improper contacts or open
circuits.




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8. Diagnostics Chart with Trouble Code

B4M0406
B4M0407A
1. CHECK RESISTANCE OF ABS SENSOR.
1) Turn ignition switch OFF.
2) Disconnect connector from ABS sensor.
3) Measure resistance between ABS sensor connector ter-
minals.
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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8. Diagnostics Chart with Trouble Code

B4M0408A
2. CHECK BODY SHORT OF ABS SENSOR.
1) Turn ignition switch OFF.
2) Disconnect connector from ABS sensor.
3) Measure resistance between ABS sensor connector ter-
minal and body.
TROUBLE CODE / Connector & terminal:
21 / (B6) No. 1—body
/ (B6) No. 2—body
23 / (B15) No. 1—body
/ (B15) No. 2—body
25 / (P8) No. 1—body
/ (P8) No. 2—body
27 / (P9) No. 1—body
/ (P9) No. 2—body
Specified resistance: 1 MΩor more
B4M0409A
3. CHECK HARNESS CONNECTOR BETWEEN ABS/
TCS CONTROL MODULE AND ABS SENSOR.
1) Turn ignition switch OFF.
2) Connect connector to ABS sensor.
3) Disconnect all connectors from ABS/TCS control mod-
ule.
4) Measure resistance between ABS/TCS control module
connector terminals.
TROUBLE CODE / Connector & terminal:
21 / (P6) No. 8—No. 16
23 / (P7) No. 1—No. 11
25 / (P7) No. 2—No. 12
27 / (P6) No. 7—No. 15
Specified resistance: 0.8—1.2 kΩ
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8. Diagnostics Chart with Trouble Code

B4M0410A
4. CHECK BODY SHORT OF HARNESS.
1) Turn ignition switch OFF.
2) Connect connector to ABS sensor.
3) Disconnect all connectors from ABS/TCS control mod-
ule.
4) Measure resistance between ABS/TCS control module
connector terminals.
TROUBLE CODE / Connector & terminal:
21 / (P6) No. 8—body
/ (P6) No. 16—body
23 / (P7) No. 1—body
/ (P7) No. 11—body
25 / (P7) No. 2—body
/ (P7) No. 12—body
27 / (P6) No. 7—body
/ (P6) No. 15—body
Specified resistance: 1 MΩor more
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8. Diagnostics Chart with Trouble Code

C: TROUBLE CODE 22, 24, 26 AND 28
—FAULTY ABS SENSOR (FAULTY ABS
SENSOR SIGNAL)—
DIAGNOSIS:

Faulty ABS sensor signal (noise, irregular signal, etc.)

Faulty hydraulic unit

Faulty harness/connector

Faulty ABS/TCS control module
TROUBLE SYMPTOM:

ABS does not operate.

TCS does not operate.

TCS operates when should not.
1. Check ABS sensor mechanical trouble.
OK
Not OK
Repair ABS sensor/tone wheel.
2. Check ground circuit of ABS/TCS control
module.
OK
Not OK
Repair harness/connector.
3. Check resistance of ABS sensor.
OK
Not OK
Replace ABS sensor.
4. Check harness connector between ABS/TCS
control module and ABS sensor.
OK
Not OK
Repair harness/connector.
5. Check sources of signal noise.
OK
Not OK
Repair noise sources.
6. Check hydraulic unit operations.
OK
Not OK
Replace hydraulic unit.
Replace ABS/TCS control module.






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8. Diagnostics Chart with Trouble Code

G4M0700
G4M0701
1. CHECK ABS SENSOR MECHANICAL TROUBLE.
1) Dismount brake as outlined in manual to gain access to
ABS 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—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)
7) The following checks can be made if an oscilloscope is
available.
(1) Raise all four wheels of ground.
(2) Turn ignition switch OFF.
(3) Connect all connectors to ABS control module.
(4) Connect the oscilloscope to the ABS control mod-
ule connector in accordance with trouble code.
(5) Turn ignition switch ON.
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8. Diagnostics Chart with Trouble Code

B4M0721A
(6) Rotate wheels and measure voltage at specified
frequency.
NOTE:
When this inspection is completed, the ABS/TCS control
module sometimes stores the trouble code.
TROUBLE CODE / Connector & terminal:
22 / (P6) No. 8—No.16 (Connect terminal to oscil-
loscope earth head.)
24 / (P7) No. 1—No.11 (Connect terminal to oscil-
loscope earth head.)
26 / (P7) No. 2—No.12 (Connect terminal to oscil-
loscope earth head.)
28 / (P6) No. 7—No.15 (Connect terminal to oscil-
loscope earth head.)
Specified voltage: 0.12—1 V (When it is 20 Hz.)
B4M0405A
2. CHECK GROUND CIRCUIT OF ABS/TCS CONTROL
MODULE.
1) Turn ignition switch OFF.
2) Disconnect connector from ABS/TCS control module.
3) Measure resistance between ABS/TCS control module
connector and body.
Connector & terminal / Specified resistance:
(P4) No. 6—body / 1Ωor less
(P5) No. 5—body / 1Ωor less
(P7) No. 15—body / 1Ωor less
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8. Diagnostics Chart with Trouble Code

B4M0407A
3. CHECK RESISTANCE OF ABS SENSOR.
1) Turn ignition switch OFF.
2) Disconnect connector from ABS sensor.
3) Measure resistance between ABS sensor connector ter-
minals.
TROUBLE CODE / Connector & terminal:
22 / (B6) No. 1—No. 2
24 / (B15) No. 1—No. 2
26 / (P8) No. 1—No. 2
28 / (P9) No. 1—No. 2
Specified resistance: 0.8—1.2 kΩ
4. CHECK HARNESS CONNECTOR BETWEEN ABS/
TCS CONTROL MODULE AND ABS SENSOR.
Check for poor contacts in plug-in connectors. Refer to
“Basic checks”in“FOREWORD”.
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8. Diagnostics Chart with Trouble Code