Infiniti QX4 (R50). Manual — part 353
SEL255W
Fail-safe System
NBEL0217
DESCRIPTION
NBEL0217S01
When the fail-safe system senses a malfunction, it deactivates
ASCD operation. The SET indicator in the combination meter will
then flash.
MALFUNCTION DETECTION CONDITIONS
NBEL0217S02
Detection conditions
ASCD operation during malfunc-
tion detection
I
ASCD steering (RESUME/ACCEL, CANCEL, SET/COAST) switch is stuck.
I
Vacuum motor ground circuit or power circuit is open or shorted.
I
Air valve ground circuit or power circuit is open or shorted.
I
Release valve ground circuit or power circuit is open or shorted.
I
Vehicle speed sensor is faulty.
I
ASCD control unit internal circuit is malfunctioning.
I
ASCD is deactivated.
I
Vehicle speed memory is can-
celed.
I
ASCD brake switch or stop lamp switch is faulty.
I
ASCD is deactivated.
I
Vehicle speed memory is not
canceled.
GI
MA
EM
LC
EC
FE
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
IDX
AUTOMATIC SPEED CONTROL DEVICE (ASCD)
Fail-safe System
EL-229
Trouble Diagnoses
NBEL0218
SYMPTOM CHART
NBEL0218S01
PROCEDURE
Diagnostic procedure
REFERENCE PAGE (EL-
)
SYMPTOM
F
AIL-SAFE
SYSTEM
CHECK
POWER
SUPPL
Y
AND
GROUND
CIRCUIT
CHECK
ASCD
BRAKE/ST
OP
LAMP
SWITCH
CHECK
ASCD
STEERING
SWITCH
CHECK
VEHICLE
SPEED
SENSOR
CHECK
ASCD
PUMP
CIRCUIT
CHECK
ASCD
ACTUA
T
OR/PUMP
CHECK
ASCD cannot be set. (“CRUISE” indica-
tor lamp does not ON.)
X
X
★
3
ASCD cannot be set. (“SET” indicator
lamp does not blink.)
X
X
X
ASCD cannot be set. (“SET” indicator
lamp blinks.
★
1)
X
X
X
X
X
Vehicle speed does not decrease after
SET/COAST switch has been pressed.
X
X
Vehicle speed does not return to the set
speed after RESUME/ACCEL switch has
been pressed.
★
2
X
X
Vehicle speed does not increase after
RESUME/ACCEL switch has been
pressed.
X
X
System is not released after CANCEL
switch (steering) has been pressed.
X
X
Large difference between set speed and
actual vehicle speed.
X
X
X
Deceleration is greatest immediately
after ASCD has been set.
X
X
X
★
1: It indicates that system is in fail-safe. After completing diagnostic procedures, perform “FAIL-SAFE SYSTEM CHECK” (EL-231) to
verify repairs.
★
2: If vehicle speed is greater than 40 km/h (25 MPH) after system has been released, pressing RESUME/ACCEL switch returns vehicle
speed to the set speed previously achieved. However, doing so when the ASCD main switch is turned to “OFF”, vehicle speed will not
return to the set speed since the memory is canceled.
★
3: Check only main switch built-in steering switch.
AUTOMATIC SPEED CONTROL DEVICE (ASCD)
Trouble Diagnoses
EL-230
SEL417V
FAIL-SAFE SYSTEM CHECK
=NBEL0218S02
1.
Turn ignition switch to ON position.
2.
Turn ASCD main switch to ON and check if the SET indicator
blinks.
If the indicator lamp blinks, check the following.
I
ASCD steering switch. Refer to EL-234.
SEL767P
3.
Drive the vehicle at more than 40 km/h (25 MPH) and push
SET/COAST switch.
If the indicator lamp blinks, check the following.
I
Vehicle speed sensor. Refer to EL-235.
I
ASCD pump circuit. Refer to EL-235.
I
Replace control unit.
SAT797A
4.
Depress brake pedal slowly (brake pedal should be depressed
more than 5 seconds).
If the indicator lamp blinks, check the following.
I
ASCD brake/stop lamp switch. Refer to EL-233.
5.
END. (System is OK.)
GI
MA
EM
LC
EC
FE
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
IDX
AUTOMATIC SPEED CONTROL DEVICE (ASCD)
Trouble Diagnoses (Cont’d)
EL-231
POWER SUPPLY AND GROUND CIRCUIT CHECK
=NBEL0218S03
1
CHECK POWER SUPPLY CIRCUIT FOR ASCD CONTROL UNIT
1. Disconnect ASCD control unit harness connector.
2. Turn ignition switch ON.
3. Check voltage between ASCD control unit harness connector terminal 5 and ground.
SEL256WB
Refer to wiring diagram in EL-227.
Yes
©
GO TO 2.
No
©
Check the following.
I
7.5A fuse (No. 11 located in the fuse block)
I
Harness for open or short
2
CHECK GROUND CIRCUIT FOR ASCD CONTROL UNIT
Check continuity between ASCD control unit harness connector terminal 17 and body ground.
SEL257WB
Refer to wiring diagram in EL-227.
Yes
©
Power supply and ground circuit is OK.
No
©
Repair harness.
AUTOMATIC SPEED CONTROL DEVICE (ASCD)
Trouble Diagnoses (Cont’d)
EL-232
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