CH21 electrical instrumentation STUDENT VERSION rev

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Chapter 21

Electrical Instrumentation

Instrument Panels

• Dashboard is called the instrument panel

• Consists of gauges, switches, and controls

Analog Display

Digital Display

Instrument Gauges

• Provide scaled information

• Require voltage regulators and sending units

• Instrument voltage regulators (IVRs) stabilize and limit voltage to gauges

• Gauge input is from a sending unit

Instrument Gauges (cont’d)

• Two Coil (Balancing Coil) Gauge

– Uses the interaction of two electromagnets and the total field effect on an armature to cause needle movement.

Balancing Coil Gauge

Instrument Gauges (cont’d)

• Bimetallic Gauges

– Are sometimes called thermoelectric gauges.

– Use two dissimilar metals to transform the

heating effect of electricity into mechanical

movement.

– Some use an instrument voltage regulator (IVR)

to provide a constant voltage to the gauge.

Basic Information Gauges

• Speedometer

• Odometer

• Oil pressure gauge

• Coolant temperature gauge

• Fuel level gauge

• Tachometer

• Charging gauges

• Older vehicles used a drive cable

• Newer vehicles use a transmission mounted vehicle speed sensor (VSS)

• The VSS sends pulses to speedometer head

• VSS information also used by cruise

control, ride control, and engine control

modules

• A mechanical odometer may be driven off speedometer shaft or by a small motor

• Electronic odometers receive VSS input

• Mileage data is stored non-volatile ROM

• Replacement odometers must represent

correct mileage

Oil Pressure Gauge

• Typical oil pressure between 45 and 70 psi

• If low pressure or engine off, no current

flows through gauge winding

• A piezoresistive sensor controls current

flow through the gauge

Coolant Temperature Gauge

• Sending unit is usually a NTC thermistor

• Low coolant temperature equals high sender resistance

• High resistance equals low current flow

Fuel Level Gauge

• Pulses to the tach usually come from

ignition module or PCM

• Uses a balanced coil gauge

• Increased engine RPM increases the pulses

to the gauge

Charging Gauges

• Most vehicles use a volt gauge or indicator light

• Older vehicles may have an ammeter

• Indicator lamp will light when charging

system voltage is less than battery voltage

Indicator and Warning Lights

• Fasten Seal Belt Indicator

– Illuminates if driver’s seat belt is not buckled

• Tire Pressure Monitor (TPM)

– May light yellow or red depending on pressure

• Brake Warning Light

– Indicates parking brake is engaged, there is low brake fluid, or a problem with the brake system

Indicator and Warning Lights

(cont’d)

• Antilock Light

– Indicates an ABS fault

• Brake Pad Indicator

– Brake sensors sense thin brake pad lining

• Stop Light Warning Light

– Illuminates if a brake light is inoperative

Indicator and Warning Lights

(cont’d)

• Traction/Stability Control Lamp

– Indicates a problem in the traction and/or

stability control system

• Check Engine Light

– On late model vehicles this indicates an

emissions system related fault has occurred

Indicator and Warning Lights

(cont’d)

• Oil Pressure Light

– May be red or yellow depending on oil pressure

• Charge Indicator Light

– If charging system voltage is below battery

voltage this light will illuminate

• Check Filler Cap

– Check and tighten fuel filler cap

Indicator and Warning Lights

(cont’d)

• Low Fuel Warning

– Indicates fuel level is below one quarter full

• Add Coolant Lamp

– Illuminates if coolant level is low

• Maintenance Reminder

– Mileage triggered light to have vehicle

inspected and serviced

Sound Warning Devices

• Used to remind drivers of certain vehicle conditions

– Fasten seat belts

– Air bag operational

– Key left in ignition

– Door ajar

– Lights left on

Driver Information Centers

• Various gauges, warning lights, and controls may be grouped together

• May also provide fuel range, economy, and usage details

• Can show average vehicle speeds, oil life

index, and various engine-operating

parameters

– Pressure sensitive touch screen.

– Energy monitor display.

General Diagnosis and Testing

• Fuses

• Indicator bulbs

• Detector switches (indicator systems)

• Sender units (gauge systems)

• IVR (gauge systems)

• Gauges (gauge systems)

Intermittent Problem Causes

• Poor mating of connector halves

• Backed out terminals

• Wire chafing

• Connector body damage

• Dirty or corroded terminals

• Poor wire-to-terminal connections