Isuzu N-Series. Service 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]
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