Infiniti QX4. Electrical System (2003 year). Manual — part 17

Component Parts and Harness Connector
Location

NBEL0370

SEL753Y

GI

MA

EM

LC

EC

FE

AT

TF

PD

AX

SU

BR

ST

RS

BT

HA

SC

IDX

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Component Parts and Harness Connector Location

EL-261

System Description

NBEL0371

Refer to Owner’s Manual for ASCD operating instructions.

POWER SUPPLY AND GROUND

NBEL0371S01

Power is supplied at all times:

쐌

through 10A fuse [No. 14, located in the fuse block (J/B)]

쐌

to the stop lamp switch terminal 1, and

쐌

through 7.5A fuse (No. 52, located in fuse and fusible link box)

쐌

to the horn relay terminals 1 and 3.

When ignition switch is in the ON or START position, power is supplied:

쐌

through 7.5A fuse [No. 11, located in the fuse block (J/B)]

쐌

to ASCD brake switch terminal 1 and

쐌

to ASCD control unit terminal 5,

쐌

through 10A fuse [No. 18, located in the fuse block (J/B)]

쐌

to park/neutral position relay terminal 1,

쐌

through 10A fuse [No. 8, located in the fuse block (J/B)]

쐌

to combination meter terminal 66, and

When park/neutral position switch is in the P or N position, ground is supplied:

쐌

to park/neutral position relay terminal 2

쐌

through park/neutral position switch and body grounds B55 and B75.

When ASCD main switch is depressed (ON), ground is supplied:

쐌

to ASCD control unit terminal 9

쐌

from ASCD steering switch terminal 4

쐌

to ASCD steering switch terminal 6

쐌

through body grounds M4, M66 and M147

then ASCD control unit holds CRUISE condition and illuminates CRUISE indicator.
Ground is supplied:

쐌

from ASCD control unit terminal 15

쐌

to combination meter terminal 46.

OPERATION

NBEL0371S02

Set Operation

NBEL0371S0201

To activate the ASCD, all following conditions must exist.

쐌

Ground is supplied to ASCD control unit terminal 9 (Main switch is in ON position.)

쐌

Power is supplied to ASCD control unit terminal 8 (Brake pedal is released and A/T selector lever is in
other than P and N position.)

쐌

Vehicle speed is between 40 km/h (25 MPH) and 144 km/h (89 MPH). (Signal from combination meter)

When the SET/COAST switch is depressed, power is supplied:

쐌

from ASCD steering switch terminal 3

쐌

to ASCD control unit terminal 11.

And then ASCD pump is activated to control throttle wire and ASCD control unit supply ground

쐌

to combination meter terminals 51 to illuminate SET indicator.

A/T Overdrive Control during Cruise Control Driving

NBEL0371S0202

When the vehicle speed is approximately 3 km/h (2 MPH) below set speed, a signal is sent

쐌

from ASCD control unit terminal 10

쐌

to TCM (transmission control module) terminal 24.

When this occurs, the TCM (transmission control module) cancels overdrive.
After vehicle speed is approximately 1 km/h (1 MPH) below set speed, overdrive is reactivated.

ASCD Shifting Control

NBEL0371S0203

During ASCD cruise, ASCD control unit controls A/T shifting to avoid uncomfortable shifting.
This is used to control the signals below.

쐌

Throttle position sensor from ECM

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

System Description

EL-262

쐌

A/T shift solenoid valve A

Coast Operation

NBEL0371S0204

When the SET/COAST switch is depressed during cruise control driving, ASCD actuator returns the throttle
cable to decrease vehicle set speed until the switch is released. And then ASCD will keep the new set speed.

Accel Operation

NBEL0371S0205

When the RESUME/ACCEL switch is depressed, power is supplied

쐌

from ASCD steering switch terminal 2

쐌

to ASCD control unit terminal 24.

If the RESUME/ACCEL switch is depressed during cruise control driving, ASCD actuator pulls the throttle cable
to increase the vehicle speed until the switch is released or vehicle speed is reached to maximum controlled
speed by the system. And then ASCD will keep the new set speed.

Cancel Operation

NBEL0371S0206

When any of following condition exists, cruise operation will be canceled.

쐌

CANCEL switch is depressed. (Power supply to ASCD control unit terminals 11 and 24)

쐌

Brake pedal is depressed. (Power supply to ASCD control unit terminal 23 from stop lamp switch)

쐌

Brake pedal is depressed or A/T selector lever is shifted to P or N position. (Power supply to ASCD con-
trol unit terminal 8 is interrupted.)

If MAIN switch is turned to OFF during ASCD is activated, all of ASCD operation will be canceled and vehicle
speed memory will be erased.

Resume Operation

NBEL0371S0207

When the RESUME/ACCEL switch is depressed after cancel operation other than depressing MAIN switch is
performed, vehicle speed will return to last set speed. To resume vehicle set speed, vehicle condition must
meet following conditions.

쐌

Brake pedal is released.

쐌

A/T selector lever is in other than P and N position.

쐌

Vehicle speed is between 40 km/h (25 MPH) and 144 km/h (89 MPH).

ASCD PUMP OPERATION

NBEL0371S03

The ASCD pump consists of a vacuum motor, an air valve and a release valve. When the ASCD activates,
power is supplied

쐌

from terminal 12 of ASCD control unit

쐌

to ASCD pump terminal 1.

Ground is supplied to vacuum motor, air valve and release valve from ASCD control unit depending on the
operated condition as shown in the below table.
The pump is connected to ASCD actuator by vacuum hose. When the ASCD pump is activated, the ASCD
pump vacuum the diaphragm of ASCD actuator to control throttle cable.

Air valve (*1)

Release valve (*1)

Vacuum motor

Actuator inner pres-
sure

ASCD not operating

Open

Open

Stopped

Atmosphere

ASCD operating

Releasing throttle
cable

Open

Closed

Stopped

Vacuum

Holding throttle
position

Closed

Closed

Stopped

Vacuum (*2)

Pulling throttle cable Closed

Closed

Operated

Vacuum

*1: When power and ground is supplied, valve is closed.
*2: Set position held.

GI

MA

EM

LC

EC

FE

AT

TF

PD

AX

SU

BR

ST

RS

BT

HA

SC

IDX

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

System Description (Cont’d)

EL-263

Schematic

NBEL0372

MEL329Q

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Schematic

EL-264

Wiring Diagram — ASCD —

NBEL0373

FIG. 1

NBEL0373S01

MEL330Q

GI

MA

EM

LC

EC

FE

AT

TF

PD

AX

SU

BR

ST

RS

BT

HA

SC

IDX

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Wiring Diagram — ASCD —

EL-265

FIG. 2

NBEL0373S02

MEL331Q

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Wiring Diagram — ASCD — (Cont’d)

EL-266

FIG. 3

NBEL0373S03

MEL332Q

GI

MA

EM

LC

EC

FE

AT

TF

PD

AX

SU

BR

ST

RS

BT

HA

SC

IDX

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Wiring Diagram — ASCD — (Cont’d)

EL-267

FIG. 4

NBEL0373S04

MEL333Q

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Wiring Diagram — ASCD — (Cont’d)

EL-268

SEL255W

Fail-safe System

NBEL0374

DESCRIPTION

NBEL0374S01

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

NBEL0374S02

Detection conditions

ASCD operation during malfunc-

tion detection

쐌

ASCD steering (RESUME/ACCEL, CANCEL, SET/COAST) switch is stuck.

쐌

Vacuum motor ground circuit or power circuit is open or shorted.

쐌

Air valve ground circuit or power circuit is open or shorted.

쐌

Release valve ground circuit or power circuit is open or shorted.

쐌

Vehicle speed sensor is malfunctioning.

쐌

ASCD control unit internal circuit is malfunctioning.

쐌

ASCD is deactivated.

쐌

Vehicle speed memory is can-
celed.

쐌

ASCD brake switch or stop lamp switch is malfunctioning.

쐌

ASCD is deactivated.

쐌

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-269

Trouble Diagnoses

NBEL0375

SYMPTOM CHART

NBEL0375S01

PROCEDURE

Diagnostic procedure

REFERENCE PAGE (EL-

)

271

272

273

274

275

275

277

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-271) 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-270

SEL417V

FAIL-SAFE SYSTEM CHECK

=NBEL0375S02

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.

쐌

ASCD steering switch. Refer to EL-274.

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.

쐌

Vehicle speed signal. Refer to EL-275.

쐌

ASCD pump circuit. Refer to EL-275.

쐌

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.

쐌

ASCD brake/stop lamp switch. Refer to EL-273.

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-271

POWER SUPPLY AND GROUND CIRCUIT CHECK

=NBEL0375S03

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-267.

Yes

䊳

GO TO 2.

No

䊳

Check the following.

쐌

7.5A fuse [No. 11, located in the fuse block (J/B)]

쐌

Harness for open or short between ASCD control unit and fuse

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-267.

Yes

䊳

Power supply and ground circuit is OK.

No

䊳

Repair harness.

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Trouble Diagnoses (Cont’d)

EL-272

ASCD BRAKE/STOP LAMP SWITCH CHECK

=NBEL0375S04

1

CHECK ASCD BRAKE SWITCH CIRCUIT

1. Disconnect ASCD control unit harness connector.
2. Turn ignition switch ON.
3. Check voltage between ASCD control unit harness connector M3 terminal 8 and ground.

SEL258WD

Refer to wiring diagram in EL-265.

OK or NG

OK

䊳

GO TO 2.

NG

䊳

Check the following.

쐌

ASCD brake switch
Refer to “Electrical Component Inspection” (EL-279).

쐌

Park/neutral position switch
Refer to “Electrical Component Inspection” (EL-279).

쐌

Park/neutral position relay

쐌

Harness for open or short

2

CHECK STOP LAMP SWITCH CIRCUIT

1. Disconnect ASCD control unit harness connector.
2. Check voltage between ASCD control unit harness connector terminal 23 and ground.

SEL259WB

Refer to wiring diagram in EL-266.

OK or NG

OK

䊳

ASCD brake/stop lamp switch is OK.

NG

䊳

Check the following.

쐌

10A fuse [No. 14, located in the fuse block (J/B)]

쐌

Harness for open or short between ASCD control unit and stop lamp switch

쐌

Harness for open or short between fuse and stop lamp switch

쐌

Stop lamp switch
Refer to “Electrical Component Inspection” (EL-279).

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-273

ASCD STEERING SWITCH CHECK

=NBEL0375S05

1

CHECK ASCD STEERING SWITCH CIRCUIT FOR ASCD CONTROL UNIT

Check voltage between ASCD control unit harness connector terminals and ground.

SEL260WC

Refer to wiring diagram in EL-266.

OK or NG

OK

䊳

ASCD steering switch is OK.

NG

䊳

GO TO 2.

2

CHECK POWER SUPPLY FOR ASCD STEERING SWITCH

Does horn work?

Yes

䊳

GO TO 3.

No

䊳

Check the following.

쐌

7.5A fuse (No. 52, located in fuse and fusible link box)

쐌

Horn relay

쐌

Horn circuit

3

CHECK ASCD STEERING SWITCH

1. Disconnect ASCD steering switch.
2. Check continuity between ASCD steering switch harness connector Z30 terminals by pushing each switch.

SEL828Y

Refer to wiring diagram in EL-266.

OK or NG

OK

䊳

Check harness for open or short between ASCD steering switch and ASCD control unit.

NG

䊳

Replace ASCD steering switch.

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Trouble Diagnoses (Cont’d)

EL-274

VEHICLE SPEED SIGNAL CHECK

=NBEL0375S06

1

CHECK SPEEDOMETER OPERATION

Does speedometer operate normally?

Yes

䊳

GO TO 2.

No

䊳

Check speedometer and ABS actuator and electric unit circuit. Refer to wiring diagram in
EL-268.

2

CHECK VEHICLE SPEED INPUT

1. Apply wheel chocks and jack up drive wheel.
2. Disconnect ASCD control unit harness connector.
3. Check voltage between control unit terminal 22 and ground with turning drive wheel slowly by hand.

SEL263WB

Refer to wiring diagram in EL-267.

Yes

䊳

Vehicle speed signal is OK.

No

䊳

Check harness for open or short between ASCD control unit terminal 22 and combination
meter terminal 13.

ASCD PUMP CIRCUIT CHECK

NBEL0375S07

1

CHECK ASCD PUMP

1. Disconnect ASCD pump connector.
2. Measure resistance between ASCD pump terminals 1 and 2, 3, 4.

SEL262WB

Refer to wiring diagram in EL-267.

OK or NG

OK

䊳

GO TO 2.

NG

䊳

Replace ASCD pump.

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-275

2

CHECK ASCD PUMP CIRCUIT

1. Disconnect ASCD control unit harness connector.
2. Check harness for open or short between ASCD control unit and ASCD pump.

SEL269WB

Refer to wiring diagram in EL-267.

OK or NG

OK

䊳

GO TO 3.

NG

䊳

Repair harness.

3

CHECK ASCD PUMP POWER SUPPLY

1. Jack-up the drive wheels.
2. Maintain the conditions below.

쐌

Vehicle speed is more than 40 km/h (25 MPH).

쐌

Main switch (CRUISE lamp) is ON.

쐌

Set/coast switch (SET lamp) is ON.

Check voltage between ASCD control unit harness connector terminal 12 and ground.

SEL381WB

Refer to wiring diagram in EL-267.

OK or NG

OK

䊳

ASCD pump power supply is OK.

NG

䊳

Replace ASCD control unit.

AUTOMATIC SPEED CONTROL DEVICE (ASCD)

Trouble Diagnoses (Cont’d)

EL-276