Isuzu N-Series. Service manual — part 1047

CAB AND CHASSIS ELECTRICAL 8-293

1-3. Odometer Does Not Function (Speedometer Is Normal)

1-4. Speedometer Needle Fluctuates (May Be Wide Fluctuation)

REPLACE THE SPEEDOMETER ASSEMBLY

N8A0300E

N8A5366E

8-294 CAB AND CHASSIS ELECTRICAL

1-5. Speedometer Needle Jumps Erratically

N8A5366E

Inspection of waveform by oscilloscope

1.

Connect a resistance of 1.3 to 5k ohm (1.4W or more) between the harness side connectors 8 B-51
and 1 B-55 of the meter.

2.

Install a speedometer tester.

3.

Turn on the starter SW.

4.

Check the waveform at the time when the vehicle speed is at 60 Km (37 mph).

Normal waveform

Approximate battery voltage

23.6 m sec.

0V

2V or less

1 2 3 4 5 6 7 8

9 10 11 12 13 14

1 2 3 4 5

6 7 8 9 10 11 12

B-51

B-55

N8A0304E

CAB AND CHASSIS ELECTRICAL 8-295

2. Tachometer
2-1. Tachometer Does Not Function

2-2. Tachometer Needle Fluctuates (May Be Wide Fluctuation)

N8A5368E

N8A5368E

8-296 CAB AND CHASSIS ELECTRICAL

2-3 Tachometer Needle Jumps Erratically

• IS THE PULSE INPUT NORMAL?

YES

NO

REPAIR A POOR CONNECTION AT THE
CONNECTORS IN THE CIRCUIT OR A FAILURE IN
THE HARNESS, OR REPLACE ENGINE SPEED
SENSOR

REPLACE THE TACHOMETER

N8A0307E