Page 199 of 558
REAR AXLE – Special Tools27-3
SPECIAL TOOLS
ToolNumberNameUse
MB991502MUT-II sub-
assemblyInspection of AYC
(diagnosis display by MUT-II)
MB991529Diagnosis code
check harnessInspection of AYC
(diagnosis display by AYC warning lamp)
MD998330
(MD998331)Oil pressure
gauge
(2,942 kPa)Hydraulic pressure measurement
MB991705Hose adapter
MB990925Bearing & oil seal
installer setPressfitting of oil seal
MB991115Oil seal installerPressfitting of oil seal
(used in combination with MB990938)
MD998812Installer capPressfitting of oil seal
nism of vehicles with AYC>
MD998813Installer 100
MD998829Installer adapter
(60)
Page 200 of 558
REAR AXLE – Special Tools / Troubleshooting 27-4
MB990925
Brass bar
Bar (one-touch type)Toolbox
Installer adapter
Tool number (MB990925)O.D. mmTool number (MB990925)O.D. mm
AMB99092639.0AMB99093363.5
MB99092745.0MB99093467.5
MB99092849.5MB99093571.5
MB99092951.0MB99093675.5
MB99093054.0MB99093779.0
MB99093157.0BMB990938–
MB99093261.0CMB990939–
TROUBLESHOOTING
BASIC TROUBLESHOOTING CONDITIONS
Refer to Group 00 – How to Use Troubleshooting / Inspection Service Points.
NOTE
Before starting the troubleshooting procedure, make sure that the following items have been checked
okay.
The correct steering wheel has been properly installed in the neutral position of the steering column
shaft.
Tire and wheel sizes are correct with correct specifications. Inflation pressure, balance, and wear
conditions are okay.
Wheel alignment is correct.
The engine, suspension, and other parts have not been remodeled so as to affect the AYC system.
DIAGNOSIS FUNCTION
READING THE DIAGNOSIS CODE
Read the diagnosis code using an MUT-II tester or the AYC warning lamp.
(Refer to Group 00 – How to Use Troubleshooting / Inspection Service Points.)
ERASING THE DIAGNOSIS CODE
Refer to Group 00 – How to Use Troubleshooting / Inspection Service Points.
Page 204 of 558
REAR AXLE – Troubleshooting 27-8
Code No. 25: Wrong-diameter tireProbable 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.Defective harness or connector
Defective AYC-ECU
Defective ABS-ECU
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-95NG
Repair
OK
Check the trouble symptom.
NO
Measure at B-95 AYC-ECU connector.
Disconnect the connector and
measure at the harness side.
Ignition switch: ON
Turn tire at 1/2 to 1 revolution/sec.
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)OKCheck the following connector:
B-95
YES
Is ABS diagnosis code No. 15 output?YESGroup 35* – Refer to Troubleshooting
Are correct tires mounted on all four
wheels?NO
Repair
NG
Repair
NO
Repair
NOCheck 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-19NG
Repair
OK
Check wheel bearing.NG
Replace
NG
Replace AYC-ECU.
OK
Check the trouble symptom.
OK
Check the following connector:
B-95NG
Repair
OK
Check wheel speed sensor output volt-
age. (Refer to p. 27-37.)NGCheck 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
Page 205 of 558
REAR AXLE – Troubleshooting 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.Defective harness or connector
Defective AYC-ECU
Defective ABS-ECU
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-95NG
Repair
OK
Check the trouble symptom.
NO
Measure at B-95 AYC-ECU connector.
Disconnect the connector and
measure at the harness side.
Ignition switch: ON
Turn tire at 1/2 to 1 revolution/sec.
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)NGCheck the following connector:
B-95
Is ABS diagnosis code No. 15 output?YESRefer to Group 35B – Troubleshooting
NG
Repair
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-19NG
Repair
OK
Check wheel bearing.NG
Replace
NG
Replace AYC-ECU.
OK
Check the trouble symptom.
OK
Check the following connector:
B-95NG
Repair
OK
Check wheel speed sensor output volt-
age. (Refer to P.27-37.)NGCheck wheel speed sensor and ABS
rotor. (Refer to Group 35B.)
Check wheel speed sensor for installa-
tion.NG
Repair
NG
Replace
Page 216 of 558
REAR AXLE – Troubleshooting 27-20
5. INSPECTION CHART FOR TROUBLE SYMPTOMS
Trouble symptomInspection
procedure No.Ref. page
Communication between MUT-II and the whole system is not possible.127-20
Communicatio between MUT-II and AYC-ECU is not possible.227-21
AYC warning lamp does not light up when the ignition key is turned to “ON” (engine
stationary).327-22
AYC warning lamp remains lit up after the engine has started.427-23
AYC is inoperative.
Unable to start or accelerate on slippery road surfaces.527-23
Rear tires are noisy during low-speed cornering.
Vehicle skews.627-24
6. INSPECTION PROCEDURE FOR TROUBLE SYMPTOMS
INSPECTION PROCEDURE 1
Communication between MUT-II and the whole system is
not possible.
Probable cause
The cause may be a malfunction of the power supply circuit or the ground circuit
of the diagnosis connector.Defective diagnosis connector
Defective harness or connector
NG
Check and repair the harness between
power supply and diagnosis connector.
OK
Check the trouble symptom.
NG
Check and repair the harness between
body ground and diagnosis connector.
OK
Check the trouble symptom.
OK
Replace MUT-II.
Check the following connectors:
B-22, B-50NG
Repair
OK
Measure at B-22 diagnosis connector.
Disconnect the connector and
measure at the harness side.
Continuity across 4/5 and body
ground
OK:ConductingNG
Measure at B-22 diagnosis combina-
tion meter connector.
Voltage across 16 and body ground
OK:System voltageNGCheck the following connectors:
B-22, B-49, B-75, B-73NG
Repair
Page 218 of 558
REAR AXLE – Troubleshooting 27-22
INSPECTION PROCEDURE 3
AYC warning lamp does not light up when the ignition key
is turned to “ON” (engine stationary).
Probable cause
The lamp power supply circuit is probably open-circuited, lamp bulb is out, or the
circuit between AYC warning lamp and AYC-ECU or AYC-ECU itself is defective.Blown fuse
AYC warning lamp out
Defective harness or connector
Defective AYC-ECU
NG
Check and repair the harness between
ignition switch (IG
2) and AYC warning
lamp.
OK
Check the trouble symptom.
OK
Replace combination meter.
NG
Check the harness between AYC
warning lamp and AYC-ECU.NG
Repair
OK
Check the trouble symptom.OK
Replace AYC-ECU.
OK
Check the following connectors:
B-96, B-94, B-08NG
Repair
OK
Measure at B-96 AYC-ECU connector.
Disconnect the connector and
measure at the harness side.
Ignition switch: ON
Warning lamp when 36 is grounded
to body
OK:Lit upNGCheck the lamp bulb.NG
Replace
Measure at B-08 combination meter
connector.
Disconnect the connector and
measure at the harness side.
Ignition switch: ON
Voltage across 48 and body ground
OK:Symptom voltageNGCheck the following connectors:
B-08, B-74, B-76NG
Repair
Page 219 of 558
REAR AXLE – Troubleshooting 27-23
INSPECTION PROCEDURE 4
AYC warning lamp remains lit up after the engine has
started.
Probable cause
The AYC warning lamp ON circuit is probably short-circuited.Defective combination meter
Defective harness (short-circuit)
Defective AYC-ECU
NOTE
This symptom is limited only when the communication with MUT-II is possible with AYC-ECU power supply
in normal condition and the diagnosis code is correct.
OK
Replace combination meter.
NO
Check the harness between AYC
warning lamp and AYC-ECU.NG
Repair
Does the AYC warning lamp goes out
when the B-96 AYC-ECU connector
is disconnected?YESReplace AYC-ECU.
INSPECTION PROCEDURE 5
AYC is inoperative.
Unable to start or accelerate on slippery road surfaces.
Probable cause
The hydraulic oil level is probably low, there is an oil leak, the hydraulic unit is defective,
or the torque transfer differential is defective.Low hydraulic oil level
Oil leak
Defective hydraulic unit
Defective torque transfer differential
NOTE
This symptom is limited only when the diagnosis code is correct.
NG
Replace the hydraulic unit.
NG
Replace the torque transfer differential.
Check the trouble symptom.
NG
Replace AYC fluid.
OK
Correct
Check the trouble symptom.NO
Replace the torque transfer differential.
OK
Is foreign matter trapped in the hydrau-
lic line?YES
Repair
OK
Check the AYC for operation.
(Refer to P.27-34.)OKCheck the AYC fluid.
NG
Add hydraulic oil.
NG
Check hydraulic pressure..
(Refer to P.27-35.)NGBleed the system of air.
(Refer to P.27-34.)
Check the hydraulic oil level.NGCheck for oil leak.OK
Repair
Page 225 of 558
REAR AXLE – Troubleshooting 27-29
Terminal
No.Normally Check requirement Check item
17Steer sensor (ST-N)Engine:
Idle speed
Steering wheel: Neutral position0.5 V or less
Idle speed
Steering wheel: Turned 90 from
neutral position2.5 – 3.5 V
18TPSIgnition switch:
ON
Accelerator pedal: Fully closed0.3 – 1.0 V
ON
Accelerator pedal: Fully open4.5 – 5.0 V
23Diagnosis data input/outputWhen MUT-II is connectedSerial communica-
tion with MUT-II
When MUT-II is disconnected1 V or less
24Idle position switchIgnition switch:
ON
Accelerator pedal: Fully closed2 V or less
ON
Accelerator pedal: Fully open4.5 – 5.0 V
25Accumulator pressure
switchIgnition switch:
ONAccumulator internal pressure:
Low2 V or less
Accumulator internal pressure:
HighSystem voltage
26ECU groundAt all times0 V
31AYC-ECU power supplyIgnition switch: ONSystem voltage
Ignition switch: OFF0 V
35AYC motor relayIgnition switch:
ON
When motor is energizedSystem voltage
ON
When motor is deenergized2 V or less
36AYC warning lampIgnition switch:
ON
When lamp is OFFSystem voltage
ON
When lamp is ON2 V or less
37Directional control valve
(right)
Ignition switch:
ON
Right clutch: ONSystem voltage
(right)ON
Right clutch: OFF0 V
38Proportioning valveIgnition switch:
ONAYC-ON0 V to system volt-
age
AYC-OFF0 V
39ECU backup power supplyAt all timesSystem voltage
45Directional control valve
(left)
Ignition switch:
ON
Left clutch: ONSystem voltage
(left)ON
Left clutch: OFF0 V
46ECU groundAt all times0 V
NOTE
*1: Indicates the vehicles with ABS.
