Chapter 21 Electrical Instrumentation Instrument Panels Dashboard is

Chapter 21 Electrical Instrumentation

Instrument Panels • Dashboard is called the instrument panel. • Consists of gauges, switches, and controls.

Types of Displays • Analog – An indicator moves in front of a fixed scale to indicate a condition. • Digital – Uses numbers or graphic symbols instead of a moving needle.

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.

Magnetic Gauges • Magnet attracts ferrous needle. • Armature field opposes PM. • Attractive or repulsive forces move needle.

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 Oil pressure gauge Coolant temperature gauge Fuel level gauge Tachometer Charging gauges

Speedometer • 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.

Odometer • 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 • Uses a variable resistor. • Low fuel level equals low resistance.

Tachometer • 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.

Hybrid Vehicles • Honda – Displays status of hybrid system, fuel economy, battery status, and charge/assist. • Toyota – 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