1. Electrical Instrumentation Operation and Service
Unit 6
Electrical Instrumentation Operation and Service

2. Introduction Gauges indicate state of operation to the driver
Gauges are used to alert driver to potential problems
Gauges today are primarily electrical, many are module controlled

3. Gauges Electrical/electronic gauges can be operated two ways:
Controlled by a module
Signal as input to module
Or received over the network
Connected directly to a sender or sensor
Gauge and sensor/sender part of the same circuit

4. Oil Indicators One of two types:
Can be variable resistor type
Can be switch
Switch type will not read variation in oil pressure
Low oil pressure indicator illuminated by
Mechanical problem with engine
Clogged pickup, worn bearings, low oil
Electrical problem with indicator circuit
High resistance, open/short in harness

5. Oil Monitoring Systems
Used to inform the driver oil needs changed
Several types:
Simple timers
By miles/time
Some calculate
Based on usage (e.g. average load, cold starts, city/highway, etc…)
Some measure directly
Measure oil conductivity
Almost all systems require reset after oil change

6. Fuel Tank Sending Unit Sending unit is a variable resistor
Potentiometer or rheostat
Must often be replaced with pump assembly
Typically 5v reference
Signal sent to
Module or
Gauge

7. Temperature Indicators
Temp indicator can be:
Gauge
Warning light
Both
Signal comes from engine coolant temp sensor
Vehicle can have more than one
(i.e. one for the ECU, one for the gauge)
Abnormal value can be:
Electrical
High resistance, open/short
Mechanical
Low coolant/air pocket, stuck open t-stat, bad pump, etc…

8. Checking Warning Device Operation
Gauge can be controlled by module or sensor
To diagnose:
Read circuit ‘Description and Operation’ (service info)
View schematic
Perform test accurately
Electrical
(e.g. voltage drop 5V reference)
Mechanical
(e.g. measure temperature w/ pyrometer)
May require scan tool

9. Summary Gauge signal from sensor or module
Abnormal values can be mechanical or electrical problems
Diagnosis requires service info, electrical and mechanical testing
Oil monitors must be reset after change

10. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.