Isuzu N-Series. Manual - part 415

6D6-6 QOS II PREHEATING SYSTEM

If the measured resistance is outside the specified
range, the glow relay must be replaced.

Thermo-Switch

Specification

• Before installing the thermo-switch, apply LOC-

TITE 262 or its equivalent to the portion shown in
the illustration.

Glow plug check

• Use the circuit tester to measure the continuity of

the glow plug.

• When the obtained value is outside the specified

range, replace the glow plug with a new one.

Glow plug resistance = About 4

Ω (at room temperature)

Notice:
When changing glow plugs, use a set of 4 glow plugs of
the same manufacture.

Glow Relay Resistance 
(Reference)

ohms

Standard

100

Operating Temperature

°C (°F)

OFF 

→ ON

7 — 13 (44.6 — 55.4)

ON 

→ OFF

Over 3 (37.4)

N6A1097E

N6A1098E

Legend

1. Pink (resin)

N6A1099E

N6A1100E

QOS II PREHEATING SYSTEM 6D6-7

• Note that an identification mark is provided to pre-

vent any possible faulty assembly.

QOS Timer

Type

Rated Voltage (V)  Total length mm (in)

Standard

23

141 (5.55)

Timer Specification

No.

Connection to

1

Starter SW “ON”

2

—

3

Thermo SW

4

Starter SW “ST”

5

Glow  relay

6

Earth (ground)

7

Indicator lamp

N6A1101E

N6A1102E

6D6-8 QOS II PREHEATING SYSTEM

TROUBLESHOOTING

Circuit diagram

Notice:
A figure in a circle “( )” shows a terminal No.
A figure in a square “[ ]” shows a circuit No.

N6A1103E

QOS II PREHEATING SYSTEM 6D6-9

When the Cooling Water Temperature is Below 0

°C (32°F).

When the Cooling Water Temperature is Over 0

°C (32°F).

Condition

Possible cause

Circuit

The glow relay does 
not turn on.

1. Defective connection in fusible link between battery and starter switch

[3]

2. Defective connection or broken wire in starter switch circuit

3. Defective connection or broken wire in fuse No.3

[2]

4. Defective starter switch

* Items 3 and 4 above coincide with troubles in other circuits.

5. Defective connection of glow relay terminal

[1]

6. Broken wire in glow relay excitation coil

7. Broken wire in the circuit between glow relay and timer

[6]

8. Defective glow relay (There is no continuity in main connection.)

9. Defective connection in QOS timer

Defective QOS timer

10. Defective ground circuit in QOS timer

[7]

11. Defective thermo-switch (The thermo-switch does not turn off even 

when water temperature is below zero.)

12. Defective ground circuit in thermo-switch

[7]

Glow relay turns on, 
but does not get pre-
heated.

1. Defective connection of fusible link between battery and start switch

[1]

2. Defective connection of glow relay main link terminal connector, or bro-

ken wire in preheating circuit

3. Defective connection of plug connector with preheating circuit

[9]

Glow relay remains 
on, and does not turn 
off.

1. Defective QOS timer

2. Circuit is shorted to ground between QOS timer terminal (5) and glow re-

lay

[6]

3. Defective glow relay

Indicator lamp does 
not light on.

1. Defective QOS timer

2. Broken wire in bulb

[8]

3. Broken wire in indicator lamp harness

Condition

Possible cause

Circuit

Indicator lamp does 
not light on.

1. Defective QOS timer

2. Broken wire in bulb

[8]

Indicator lamp lights 
on for a long time.

1. Defective thermo-switch, or broken wire in thermo-switch circuit (Indica-

tor lights on for about 3.5 sec.)

[4]

2. Defective QOS timer

Glow relay is ready to 
turn on, or remains on.

1. Circuit is shorted to ground between terminal (5) and glow relay.

[6]