Mitsubishi Lancer Evolution VI. Manual - part 53

REAR AXLE – 

Troubleshooting <AYC>

27-6

4. INSPECTION PROCEDURES FOR DIAGNOSIS CODES

Code No. 12: Power supply voltage (valve power supply)
system

Probable cause

This code is output when the AYC-ECU power supply voltage drops below, goes
beyond, a specified level.

D

Defective harness or connector

D

Defective battery

D

Defective AYC-ECU

NOTE
Refer to the corresponding item if any other diagnosis code is being output.

Is the battery voltage correct?

NG

Replace

OK

Measure at B-96 AYC-ECU connector.

D

Disconnect the connector and
measure at the harness side.

D

Ignition switch: ON

D

Voltage across 31 and body ground
OK: System voltage

NG

Check the following connectors:
B-96, B-94, B-49, B-75, B-76

OK

Check the trouble symptom.

NG

Check and repair harness between
ignition switch (IG

2

) and AYC-ECU.

OK

Replace AYC-ECU.

NG

Repair

Code Nos. 21, 22, 23, 24: Wheel speed sensor system

Probable cause

This code is output if any one of three wheel speed sensors fails to provide an input
even after the other wheel exceeded 8 km/h.

D

Defective harness or connector

D

Defective ABS-ECU

D

Defective AYC-ECU

<Vehicles with ABS>

NG

Replace AYC-ECU.

OK

Replace ABS-ECU.

NG

Check harness between AYC-ECU
and ABS-ECU.

NG

Repair

OK

Check the trouble symptom.

Is an ABS diagnosis code No. 21, 22,
23, or 24 output?

YES

Refer to Group 35B – Troubleshooting

NO

Measure at B-95 AYC-ECU connector.

D

Disconnect the connector and
measure at the harness side.

D

Ignition switch: ON

D

Turn tire at 1/2 to 1 revolution/sec.

D

Voltage across 6/7/8/9 and body
ground
OK: 42 mV or more (when mea-

sured with a circuit tester)
120 mV-P or more (when
measured with an oscillo-
scope)

OK

Check the following connector:
B-95

OK

Check the trouble symptom.

NG

Check the following connectors:
B-24, B-95

NG

Repair

NG

Repair

REAR AXLE – 

Troubleshooting <AYC>

27-7

<Vehicles without ABS>

OK

Check the wheel bearing.

NG

Check and repair the harness between
wheel speed sensor and AYC-ECU.

NG

Replace AYC-ECU.

OK

Check the trouble symptom.

OK

Check the following connector:
B-95

NG

Repair

OK

Check the trouble symptom.

OK

Check the following connectors:
B-95, B-52, B-17, A-26, A-50, D-04,
D-14, D-19

NG

Repair

OK

Measure at B-95 AYC-ECU connector.

D

Disconnect the connector and
measure at the harness side.

D

Resistance across 7-20 (front, LH),
6-19 (front, RH), 9-22 (rear, LH),
and 8-21 (rear, RH).
OK: 1.4  – 1.8 k

Ω

.

NG

Check the wheel speed sensor. (Refer
to Group 35B.)

Check the installation of wheel speed
sensor.

NG

Repair

OK

Check the wheel speed sensor output
voltage. (Refer to P.27-37)

NG

Check the wheel speed sensor and
ABS rotor. (Refer to Group 35B.)

NG

Replace

NG

Replace

REAR AXLE – 

Troubleshooting <AYC>

27-8

Code No. 25: Wrong-diameter tire

Probable cause

This code is output if the speed of any one of the four wheels exceeds a specified
level with respect to the average of the four wheel speed sensor outputs when the
steering wheel is in the straight-ahead position and the vehicle speed exceeds 20
km/h. At this time, the warning lamp does not light up.

D

Defective harness or connector

D

Defective AYC-ECU

D

Defective ABS-ECU

<Vehicles with ABS>

OK

Replace ABS-ECU.

NG

Check harness between AYC-ECU
and ABS-ECU.

NG

Repair

NG

Replace AYC-ECU.

OK

Check the trouble symptom.

NG

Check the following connectors:
B-24, B-95

NG

Repair

OK

Check the trouble symptom.

NO

Measure at B-95 AYC-ECU connector.

D

Disconnect the connector and
measure at the harness side.

D

Ignition switch: ON

D

Turn tire at 1/2 to 1 revolution/sec.

D

Voltage across 6/7/8/9 and body
ground.
OK: 42 mV or more (when mea-

sured with a circuit tester)
120 mV-P or more (when
measured with an oscillo-
scope)

OK

Check the following connector:
B-95

YES

Is ABS diagnosis code No. 15 output?

YES

Group 35* – Refer to Troubleshooting

Are correct tires mounted on all four
wheels?

NO

Repair

NG

Repair

<Vehicles without ABS>

NO

Repair

NO

Check and repair the harness between
wheel speed sensor and AYC-ECU.

OK

Check the trouble symptom.

OK

Check the following connectors:
B-95, B-52, B-17, A-26, A-50, D-04,
D-14, D-19

NG

Repair

OK

Check wheel bearing.

NG

Replace

NG

Replace AYC-ECU.

OK

Check the trouble symptom.

OK

Check the following connector:
B-95

NG

Repair

OK

Check wheel speed sensor output volt-
age. (Refer to p. 27-37.)

NG

Check wheel speed sensor and ABS
rotor. (Refer to Group 35B.)

YES

Check Wheel speed sensor for instal-
lation.

NG

Repair

Are correct tires mounted on all four
wheels?

NG

Replace

REAR AXLE – Troubleshooting <AYC>

27-9

Code No. 26: Wheel speed sensor system (faulty output
signal)

Probable cause

This code is output if the speed of one of the four wheels exceeds a specified level
when the vehicle speed is 20 km/h or more. At this time, the warning lamp is turned
on.

D

Defective harness or connector

D

Defective AYC-ECU

D

Defective ABS-ECU

<Vehicles with ABS>

OK

Replace ABS-ECU.

NG

Check harness between AYC-ECU
and ABS-ECU.

NG

Repair

NG

Replace AYC-ECU.

OK

Check the trouble symptom.

NG

Check the following connectors:
B-24, B-95

NG

Repair

OK

Check the trouble symptom.

NO

Measure at B-95 AYC-ECU connector.

D

Disconnect the connector and
measure at the harness side.

D

Ignition switch: ON

D

Turn tire at 1/2 to 1 revolution/sec.

D

Voltage across 6/7/8/9 and body
ground.
OK: 42 mV or more (when mea-

sured with a circuit tester)
120 mV-P or more (when
measured with an oscillo-
scope)

NG

Check the following connector:
B-95

Is ABS diagnosis code No. 15 output?

YES

Refer to Group 35B – Troubleshooting

NG

Repair

<Vehicles without ABS>

NG

Check and repair the harness between
wheel speed sensor and AYC-ECU.

OK

Check the trouble symptom.

OK

Check the following connectors:
B-95, B-52, B-17, A-26, A-50, D-04,
D-14, D-19

NG

Repair

OK

Check wheel bearing.

NG

Replace

NG

Replace AYC-ECU.

OK

Check the trouble symptom.

OK

Check the following connector:
B-95

NG

Repair

OK

Check wheel speed sensor output volt-
age. (Refer to P.27-37.)

NG

Check wheel speed sensor and ABS
rotor. (Refer to Group 35B.)

Check wheel speed sensor for installa-
tion.

NG

Repair

NG

Replace