Isuzu N-Series. Manual - part 1048

CAB AND CHASSIS ELECTRICAL 8-297

3. Coolant Temperature Gauge
3-1. Coolant Temperature Gauge Needle Does Not Move

• IS THE CONNECTOR OF THE THERMO UNIT

CONNECTED SECURELY?

• DISCONNECT THE CONNECTOR OF THE THERMO

UNIT

• CONNECT A 3.4W BULB BETWEEN THE HARNESS

SIDE CONNECTOR 1  E-7  AND THE GROUND OF THE
THERMO UNIT

• WHEN THE STARTER SW IS TURNED ON, DOES THE

TEMPERATURE GAUGE NEEDLE MOVE ABOUT 10
SECONDS AFTER THAT?

• IS THE THERMO UNIT NORMAL?

YES

NO

REPAIR A POOR
CONNECTION AT THE
CONNECTOR

REPLACE THE
THERMO UNIT

YES

YES

NO

YES

• IS THERE A BROKEN

WIRE IN THE PRINTED
CIRCUIT OF THE
METER ASSEMBLY?

YES

NO

REPLACE THE PRINTED
CIRCUIT BOARD

CHECK THE COOLANT
TEMPERATURE GAUGE
AND REPLACE IT WITH A
CORRECT ONE IF
NECESSARY

• REPAIR A POOR

CONNECTION AT THE
CONNECTORS OR AN
OPEN CIRCUIT IN THE
CIRCUIT

NO

• IS THE CIRCUIT BETWEEN THE TEMPERATURE

GAUGE AND THE THERMO UNIT NORMAL?

NO

CONNECT THE CONNECTOR SECURELY

N8A0308E

8-298 CAB AND CHASSIS ELECTRICAL

3-2. Coolant Temperature Gauge Reading Is Too Low (or High)

• DOES THE THERMOSTAT OPERATE NORMALLY?

• TURN THE STARTER SWITCH ON

• WHEN INSERTING AND PULLING OUT THE

THERMOSTAT CONNECTOR 1  E-7  SEVERAL
TIMES, DOES THE INDICATION OF THE COOLANT
TEMPERATURE GAUGE VARY?

• IS THE THERMO UNIT NORMAL?

REPAIR A POOR CONNECTION AT THE CONNECTOR
OF THE THERMO UNIT

• IS THERE AN OPEN CIRCUIT IN THE METER

ASSEMBLY PRINTED CIRCUIT BOARD?

REPLACE THE THERMO UNIT

YES

YES

NO

YES

NO

YES

NO

REPLACE THE PRINTED CIRCUIT BOARD

CHECK THE COOLANT TEMPERATURE GAUGE AND
REPLACE IT IF FOUND DEFECTIVE

NO

REPLACE THE THERMOSTAT

N8A0309E

CAB AND CHASSIS ELECTRICAL 8-299

3-3. Needle Overshoots (or Goes Up to the “H” Range)

• DISCONNECT THE CONNECTOR OF THE THERMO

UNIT

• WHEN THE STARTER SW IS TURNED ON, DOES

THE POINTER REACH TO THE "H" RANGE?

• IS THERE A SHORT CIRCUIT BETWEEN THE

THERMO UNIT AND THE COOLANT
TEMPERATURE GAUGE?

REPLACE THE THERMO UNIT

• IS THE PRINTED CIRCUIT OF THE METER

ASSEMBLY GROUNDED SECURELY?

REPAIR A SHORT CIRCUIT

YES

YES

NO

YES

NO

NO

REPAIR OR REPLACE THE PRINTED CIRCUIT BOARD

CHECK THE COOLANT TEMPERATURE GAUGE AND
REPLACE IT IF FOUND ABNORMAL

N8A0310E

8-300 CAB AND CHASSIS ELECTRICAL

4. Fuel Gauge
4-1. Fuel Gauge Needle Does Not Move

• IS THE CONNECTOR OF THE FUEL TANK UNIT  J-28

CONNECTED SECURELY?

• DISCONNECT THE CONNECTOR OF THE FUEL

TANK UNIT 

• CONNECT A 3.4W BULB BETWEEN THE HARNESS

SIDE CONNECTOR 1  J-28  AND THE GROUND OF
THE FUEL TANK UNIT

• WHEN THE STARTER SW IS TURNED ON, DOES THE

FUEL GAUGE NEEDLE FLUCTUATE AFTER ABOUT 90
SECONDS?

• IS THERE CONTINUITY BETWEEN THE FUEL

TANK UNIT CONNECTOR TERMINALS 1  J-28
AND 3  J-28  ?

YES

NO

REPLACE THE FUEL
TANK UNIT

REPAIR A POOR
CONNECTION AT THE
CONNECTORS OR AN
OPEN CIRCUIT
BETWEEN THE FUEL
TANK UNIT AND THE
METER

YES

YES

NO

YES

• IS THERE A BROKEN

WIRE IN THE PRINTED
CIRCUIT OF THE
METER ASSEMBLY?

YES

NO

CHECK THE FUEL
METER, AND REPLACE IT
IF NECESSARY

REPLACE THE PRINTED
CIRCUIT BOARD

REPAIR A POOR
CONNECTION AT THE
CONNECTORS OR AN
OPEN CIRCUIT IN THE
CIRCUIT

NO

• IS THE CIRCUIT BETWEEN THE FUEL GAUGE AND

THE FUEL TANK UNIT NORMAL?

NO

CONNECT THE CONNECTOR SECURELY

N8A0311E