Electrical Instrumentation Operation and Service Unit 6 Electrical Instrumentation Operation and Service

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

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

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

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

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

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…

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

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

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