Isuzu N-Series. Service manual — part 284

HSA (HILL START AID) 5A5-15

Procedure of Trouble Diagnosis

Description of Diagnosis

HSA diagnostic procedure is classified into two kinds;
one is with diagnostic trouble codes indicated by blink-
ing pattern of the HSA indicator lamp, and the other is
from trouble symptoms. Refer to “Diagnostics with diag-
nostic trouble code” in the first case, and “Diagnostics
with Phenomenon” in the latter case for diagnostic pro-
cedures.

Self-diagnosis

The HSA can perform the self-diagnosis when a mal-
function occurs in the system.
Perform the self-diagnosis in the following procedure.
HSA indicates the result in the lamp blinking pattern and
the buzzer.

1. Park the vehicle and apply the parking brake.
2. Press the adjust switch “FAST” or “SLOW” and

hold it. Self-diagnosis display continues while the
switch is pressed.

3. While pressing the switch, diagnostic trouble

codes (DTC) are displayed with the HSA indicator
lamp blinking pattern. Buzzer beeps in synchroni-
zation with lamp while displaying the trouble code.

Caution:

DTCs are displayed for three times each in turn. After
taking a round, the DTCs are displayed in the same or-
der repeatedly.

• When multiple number of trouble code stored;

Code 25/Code 91

N5A3019E

N5A3020E

5A5-16 HSA (HILL START AID)

Basic Diagnostic Procedure

Caution:

• Always perform the diagnosis in a predetermined

sequence before performing the HSA system re-
pair.

• After repair, make sure the HSA system operate/

stop normally, and the trouble code does not ap-
pear again.

• Use the harness side (body side) connector to

check for continuity (resistance) and voltage un-

less specified. Also, be especially careful not to
damage the connector terminals with the tester etc.

• Check for continuity (resistance) with the starter

switch OFF, and voltage with the starter switch ON.

• HSA control unit, HSA valve, clutch sensor, and

speed sensor are non-disassembled parts; do not
loosen the bolts and nuts.

• Do not directly apply external voltage to the HSA

control unit, the clutch sensor, and the speed sen-
sor. Use special care for electrostatic.

Step

Action

Value

YES

NO

1

Turn the HSA off switch OFF.

Does the HSA lamp blink?

—

Go to Step2

Go to Step3

2

Is there any trouble code?

—

Go to Step6, 7

Go to Step4, 5

3

Is the trouble reappeared?

—

Go to Step4, 5

Go to Step4, 5

4

What is the trouble symptom?

—

Go to Step5

Go to Step4

5

Has “Diagnostics with phenomenon” been
performed?

—

Go to Step8

Go to Step5

6

Take notes all the trouble code appeared.

What is the trouble code?

—

Go to Step7

Go to Step6

7

Has “Diagnostics with diagnostic trouble
code” been performed?

—

Go to Step8

Go to Step7

8

Has the trouble part corrected?

—

End.

Go to Step8

No.

Circuit to be

checked

Power

switch

position

Tester

scale/
range

Terminal No.

Standard value

Remarks

1

Door switch cir-
cuit

—

DCV

1 (+) — 30 (

−)

0 V

Door open *Note

—

DCV

1 (+) — 30 (

−)

Approx. 24 V

Door closed *Note

2

Stop lamp
switch circuit

—

DCV

19 (+) — 30 (

−)

0 V

—

DCV

19 (+) — 30 (

−)

Approx. 24 V

Brake pedal depressed

3

Power supply
circuit

—

DCV

29 (+) — 30 (

−)

Approx. 24 V

OFF

DCV

14 (+) — 30 (

−)

0 V

ON

DCV

14 (+) — 30 (

−)

Approx. 24 V

4

Clutch fluid
pressure switch
circuit

ON

DCV

6 (+) — 30 (

−)

0 V

ON

DCV

6 (+) — 30 (

−)

Approx. 24 V

Clutch pedal depressed

5

HSA reset
switch circuit

ON

DCV

7 (+) — 30 (

−)

0 V

ON

DCV

7 (+) — 30 (

−)

Approx. 24 V

Switch ON

6

HSA adjust
switch circuit

ON

DCV

15 (+) — 30 (

−)

0 V

ON

DCV

21 (+) — 30 (

−)

0 V

ON

DCV

15 (+) — 30 (

−)

Approx. 24 V

Switch “SLOW” side

ON

DCV

21 (+) — 30 (

−)

Approx. 24 V

Switch “FAST” side

7

HSA off switch
circuit

ON

DCV

13 (+) — 30 (

−)

Approx. 24 V

Switch OFF

ON

DCV

13 (+) — 30 (

−)

0 V

Switch ON

HSA (HILL START AID) 5A5-17

*Note: Position the room lamp switch at door interlock.

Function Check

HSA Adjustment

The HSA memorize the clutch meeting point to release
the brake force. Therefore, releasing point must be ad-
justed after clutch replacement or clutch play adjust-

ment. Adjustment contains the “Initial adjustment” to
memorize the clutch pedal position to release the HSA
brake force, and the “Brake release adjustment” to fine
adjustment of the clutch pedal position to release the
brake for smooth starting of the vehicle.

Initial Adjustment

1. Start the engine.
2. Make sure that the HSA off switch is not pressed

(HSA in operation).

3. Apply the parking brake.
4. Disengage the clutch, move the gear position to

2nd, and press the HSA reset switch. (Buzzer
(bleep*) continues at this time.)

5. Slowly release the clutch pedal, and press the

“SLOW” or “FAST” of the HSA adjust switch when
the engine speed goes down to 30 — 50 rpm lower
than the idle speed. (Buzzer (bleep*) stops at this
time.)

6. Move the gear back to neutral and slowly engage

the clutch. In case when the buzzer goes off while
in operation or when the HSA adjust switch is
pressed by accident, retry the procedure from step
3.

Brake Release Adjustment

1. Start the engine.
2. Make sure that the HSA off switch is not pressed

(HSA in operation).

3. Depress the brake, make sure the gear is in neu-

tral, and release the parking brake lever.

8

HSA valve cir-
cuit

OFF

Ω

8 — 28

111.6

±10%

HSA off switch
depressed, Control unit
removed

9

Neutral
switch circuit

ON

DCV

18 (+) — 30 (

−)

0 V

Gear except in “Neutral”

ON

DCV

18 (+) — 30 (

−)

Approx. 24 V

Gear in “Neutral”

10

Parking brake
switch circuit

ON

DCV

2 (+) — 30 (

−)

Approx. 24 V

Parking brake released

ON

DCV

2 (+) — 30 (

−)

0 V

Parking brake applied

11

HSA indicator
lamp circuit

ON

DCV

12 (+) — 30 (

−)

Approx. 24 V

With indicator lamp OFF

ON

DCV

12 (+) — 30 (

−)

0 V

With indicator lamp ON

12

Clutch sensor
circuit

OFF

Ω

24 — 26

2k

Ω±400Ω

OFF

Ω

25 — 26

400

Ω — 2.8kΩ

Clutch pedal operated

ON

DCV

24 (+) — 30 (

−)

4.5 V or more

ON

DCV

25 (+) — 30 (

−)

0.5V

±0.2V

Clutch pedal released
(clutch fully engaged)

13

Speed sensor
circuit

ON

DCV

17 (+) — 30 (

−)

2V or 14V

14

Generator L ter-
minal circuit

ON

DCV

10 (+) — 30 (

−)

0 V

Engine stopping

ON

DCV

10 (+) — 30 (

−)

Approx. 24 V

Engine running

No.

Circuit to be

checked

Power

switch

position

Tester

scale/
range

Terminal No.

Standard value

Remarks

Vehicle condition when adjustment is needed

Necessary adjustment

When the clutch-related parts are replaced, or clutch pedal play is
adjusted. When the brake release timing is considerably fast/slow. When
the brake drags at vehicle starting.

Initial adjustment

When the brake drags at vehicle starting. When the vehicle moves back
at starting on a graded road. When the brake release timing does not
match with the feeling.

Brake release adjustment (FAST)
(SLOW) (FAST OR SLOW)

5A5-18 HSA (HILL START AID)

4. Check that the HSA indicator lamp is ON, disen-

gage the clutch, and move the gear except in neu-
tral position.

5. When the brake release is too slow that the brake

drags at vehicle starting, press the “FAST” of the
adjust switch.
When the brake release is too fast that the vehicle
moves back at starting on a graded road, press the
“SLOW” of the adjust switch.

Caution:

Each time pressing the switch, the buzzer bleeps. The
number of times pressing the switch increase to the de-
gree of change where to release the brake force at high-
er/lower clutch pedal position.

6. When the brake release timing does not match with

the feeling, retry the procedure from step 3.
(Start over from the initial adjustment if messed
up.)

List of Diagnostic Trouble Code

About Diagnostic Trouble Code

The control unit clears the fault code when the fault part
is judged to be normal.

Number of

times

pressing the

switch

1 — 2 times Fine adjustment “FAST” “SLOW”

2 — 3 times

When brake drags “FAST”
When the vehicle on a graded road
moves back. “SLOW”

3 — 5 times

When brake drags. “FAST”
When the vehicle on a graded road
moves back. “SLOW”

Code

Diagnosis item

01

Normal code

03

Back-up fuse open

08

Clutch sensor output voltage fault

19

Adjust switch “FAST” or “SLOW” is ON even when out of the adjustment limit, or adjust switch
“FAST” or “SLOW” is ON when the vehicle speed 5 km/h (3 mph) or more.

25

Vehicle speed sensor output voltage fault

33

Control unit fault

36

Generator L terminal output does not exist even when the clutch is engaged and the gear is
shifted with vehicle running.

86

Clutch fluid pressure switch does not turn ON with clutch pedal depressed, and it turns ON
with the clutch engaged. (Clutch fluid pressure switch fault)

91

Solenoid valve drive signal and solenoid valve monitor conditions are erratic. (HSA valve fault)

Vehicle motion

alarm

Detects vehicle speed 1.5km/h (1 mph) or more with solenoid valve operated and gear in neu-
tral.

Longtime alarm

Solenoid valve has operated for more than 8 minutes continuously with brake not depressed.