OBJECTIVES

2. OBJECTIVES After studying Chapter 23, the reader should be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “F” (Gauges,Warning Devices, and Driver Information System Diagnosis and Repair). • Discuss how a fuel gauge works. • Explain how to use a service manual to troubleshoot a malfunctioning dash instrument. • Describe how a navigation system works. • List the various types of dash instrument displays.

3. ANALOG DASH INSTRUMENTS • Two basic types of analog (needle-type) dash instrument gauges used on older vehicles were the electromagnetic and the thermoelectric gauges.

4. ANALOG DASH INSTRUMENTSThermoelectric Gauges • This type of gauge moves very slowly, which is an advantage, because turns and hills do not affect the readings of the fuel gauge, for example, and the needle tends to remain steady. FIGURE 23-1 A thermoelectric fuel gauge has 5 volts coming from the instrument voltage regulator (IVR). The IVR is shared by all other dash instruments. Electronic gauges use the same sensor (sending unit) but use electronic circuits to control needle movement or digital display.

5. ANALOG DASH INSTRUMENTSThermoelectric Gauges • If all dash instruments are functioning incorrectly, as when all are reading high or low, the usual cause is the instrument voltage regulator located on the back of the instrument panel. FIGURE 23-2 Instrument voltage regulator. Vibrating points maintain current through the instrument at 5 volts. The radio choke prevents radio interference created by the pulsing current low.

6. ANALOG DASH INSTRUMENTSElectromagnetic Gauges • Electromagnetic dash instruments use small electromagnetic coils that are connected to a sending unit for such things as fuel level, water temperature, and oil pressure. • The resistance of the sensor varies with what is being measured.

7. ANALOG DASH INSTRUMENTSElectromagnetic Gauges FIGURE 23-3 Electromagnetic fuel gauge wiring. If the sensor wire is unplugged and grounded, the needle should point to “E” (empty). If the sensor wire is unplugged and held away from ground, the needle should point to “F” (full).

8. COMPUTER-CONTROLLED INSTRUMENT PANELS • Many instrument panels are operated by electronic control units that communicate with the engine control computer for engine data such as revolutions per minute (RPM) and engine temperature. FIGURE 23-4 Many vehicles use a computer display for certain functions including trip computers, radio, clock, and air conditioning. This vehicle is not moving and yet the engine is running, so the fuel economy is zero.

9. FIND SERVICE INFORMATION AND USE IT • Today’s electronic circuits are often too complex to show on a wiring diagram. • Even if all electronic circuitry was shown on the wiring diagram, it would require the skill of an electronics engineer to determine exactly how the circuit was designed to work.

10. FIND SERVICE INFORMATION AND USE IT FIGURE 23-5 The ground for the “check oil” indicator lamp is controlled by the electronic low-oil buffer. Even though this buffer is connected to an oil level sensor, the buffer also takes into consideration the amount of time the engine has been stopped and the temperature of the engine. The only way to properly diagnose a problem with this circuit is to use the procedures specified by the vehicle manufacturer. Besides, only the engineer that designed the circuit knows for sure how it is supposed to work.

11. STEPPER MOTOR GAUGES • Most analog dash displays use a stepper motor to move the needle. • A stepper motor is a type of electric motor that is designed to rotate in small steps based on the signal from a computer. • This type of gauge is very accurate.

12. HEAD-UP DISPLAY • The head-up display (HUD) is a supplemental display that projects the vehicle speed and sometimes other data, such as turn signal information, onto the windshield. • The projected image looks as if it is some distance ahead, making it easy for the driver to see without having to refocus on a closer dash display.

13. HEAD-UP DISPLAY FIGURE 23-6 A typical head-up display showing zero miles per hour, which is actually projected on the windshield from the head-up display in the dash. FIGURE 23-7 The dash-mounted control for the head-up display on this Cadillac allows the driver to move the image up and down on the windshield for best viewing.

14. HEAD-UP DISPLAY • The HUD unit is installed in the instrument panel (IP) and uses a mirror to project vehicle information onto the inside surface of the windshield. FIGURE 23-8 A typical HUD unit.

15. NIGHT VISIONParts and Operation • Night vision systems use a camera that is capable of observing objects in the dark to assist the driver while driving at night. • The camera is mounted behind the grill in the front of the vehicle. FIGURE 23-9 A night vision camera in the front of a Cadillac.

16. NIGHT VISIONParts and Operation • Other parts of the night vision system include: • On/off and dimming switch—This allows the driver to adjust the brightness of the display and to turn it on or off as needed. • Up/down switch—The night vision HUD system has an electric tilt adjust motor that allows the driver to adjust the image up or down on the windshield within a certain image.

17. NIGHT VISIONDiagnosis and Service • The first step when diagnosing a fault with the night vision system is to verify the concern. • For example, the Cadillac night vision system requires the following actions to function. • The ignition has to be in the on (run) position. • The Twilight Sentinel photo cell must indicate that it is dark. • The headlights must be on. • The switch for the night vision system must be on and the brightness adjusted so the image is properly displayed.

18. DASH INSTRUMENT DIAGNOSIS • With electromagnetic gauges, if the resistance of the sensor is low, the meter reads low. • If the resistance of the sensor is high, the meter reads high.

19. TELLTALE LAMPS • Telltale lamps (often called idiot lights) warn the driver of system failure. • When the ignition is turned on, all warning lamps come on as a bulb check. • The charging system warning lamp may be labeled “CHARGE,” “GEN,” or “ALT” and will light if the charging system fault is detected. FIGURE 23-10 This symbol is used to represent a charging circuit problem.

20. OIL PRESSURE WARNING DEVICES • The oil pressure lamp operates through use of an oil pressure sensor unit, which is screwed into the engine block, and grounds the electrical circuit and lights the dash warning lamp in the event of low oil pressure (3 to 7 psi [20 to 50 kilopascals, kPa]). FIGURE 23-11 This oil pressure grounding switch (sending unit) has a fixed contact connected to ground and a contact that is moved by the pressure sensitive diaphragm.

21. OIL PRESSURE WARNING DEVICES • Normal oil pressure is generally between 10 and 60 psi (70 and 400 kPa). FIGURE 23-12 A typical oil pressure sending unit provides a varying amount of resistance as engine oil pressure changes.

22. OIL PRESSURE WARNING DEVICESOil Pressure Lamp Diagnosis • To test the operation of the oil pressure warning circuit, unplug the wire from the oil pressure sending unit, usually located near the oil filter, with the ignition switch on. FIGURE 23-13 A Ford oil pressure sending unit. Most oil pressure sending units are located near the oil filter and are threaded into an oil gallery.

23. TEMPERATURE LAMP DIAGNOSIS • Always check the cooling system operation and the operation of the warning lamp circuit when the hot lamp comes on during normal driving. FIGURE 23-14 Temperature grounding switches expose a bimetallic strip to engine coolant temperature to light a high-temperature lamp or both high- and low-temperature warning lamps.

24. BRAKE WARNING LAMP • All vehicles sold in the United States after 1967 must be equipped with a dual braking system and a dash-mounted warning lamp to signal the driver of a failure in one part of the hydraulic brake system. FIGURE 23-15 Typical red brake warning lamp.

25. BRAKE WARNING LAMP • If there is unequal hydraulic pressure in the braking system, the switch usually grounds the 12 volt lead at the switch and the lamp comes on. FIGURE 23-16 Typical brake warning light switch located on or near the master brake cylinder.

26. BRAKE WARNING LAMP • The red brake warning lamp also can be turned on if the brake fluid is low. FIGURE 23-17 The red brake warning lamp can be turned on if the brake fluid level is low.

27. DIGITAL ELECTRONIC DASH OPERATION • Mechanical or electromechanical dash instruments use cables, mechanical transducers, and sensors to operate a particular dash instrument. • Electronic dash display systems may use one or more of the several types of displays: light-emitting diode (LED), liquid crystal display (LCD), vacuum tube fluorescent (VTF), and cathode ray tube (CRT).

28. DIGITAL ELECTRONIC DASH OPERATIONLED Digital Displays • All diodes emit some form of energy during operation; the light-emitting diode (LED) is a semiconductor that is constructed to release energy in the form of light. FIGURE 23-18 (a) Symbol and line drawing of a typical light emitting diode (LED). (b) Grouped in seven segments, this array is called a seven segment LED display with a common anode (positive connection). The dash computer toggles the cathode (negative) side of each individual segment to display numbers and letters. (c) When all segments are turned on, the number 8 is displayed.

29. DIGITAL ELECTRONIC DASH OPERATIONLiquid Crystal Displays • Liquid crystal displays (LCDs) can be arranged into a variety of forms, letters, numbers, and bar graph displays. • The light from a very bright halogen bulb behind the LCD shines through those segments of the LCD that have been polarized to let the light through, which then show numbers or letters.

30. DIGITAL ELECTRONIC DASH OPERATIONVacuum Tube Fluorescent Displays • The vacuum tube fluorescent (VTF) display is a popular automotive and household appliance display because it is very bright and can easily be viewed in strong sunlight. • Most VTF displays are green for best viewing under most lighting conditions.

31. DIGITAL ELECTRONIC DASH OPERATIONCathode Ray Tube • A cathode ray tube (CRT) dash display, which is similar to a television tube or LCD display, permits the display of hundreds of controls and diagnostic messages in one convenient location. FIGURE 23-19 A typical navigation system. This Acura system incorporates some of the climate control functions as well as the trip information on the display. This particular unit uses a DVD unit in the trunk along with a global positioning satellite (GPS) to display a map and your exact location for the entire country.

32. DIGITAL ELECTRONIC DASH OPERATION Cold Cathode Fluorescent Displays • Cold cathode fluorescent lighting (CFL) models are used by many vehicle manufacturers for backlighting. • CFL is replacing conventional incandescent light bulbs.

33. DIGITAL ELECTRONIC DASH OPERATIONElectronic Analog Displays • A scan tool often is needed to diagnosis the operation of a computer-controlled analog dash instrument display. FIGURE 23-20 (a) View of the vehicle dash with the instrument cluster removed. Sometimes the dash instruments can be serviced by removing the padded dash cover (crashpad) to gain access to the rear of the dash. (b) The front view of the electronic analog dash display. (c) The rear view of the dash display showing that there are a few bulbs that can be serviced, but otherwise the unit is serviced as an assembly.

34. DIGITAL ELECTRONIC DASH OPERATIONOther Electronic Gauge Displays • Oil pressure, water temperature, and voltmeter readings are other commonly used electronic dash displays. • A warning lamp is often part of the electronic circuits in the electronic display to warn the driver of high or low battery voltage.

35. DIGITAL ELECTRONIC DASH OPERATIONThe WOW Display • When a vehicle equipped with a digital dash is started, all segments of the electronic display are turned on at full brilliance for 1 or 2 seconds. • Technicians can also use the WOW display to determine if all segments of the electronic display are functioning correctly.

36. THE BULB TEST • Many ignition switches have six positions. FIGURE 23-22 Many newer vehicles place the ignition switch on the dash and incorporate antitheft controls. Note the location of the accessory position. FIGURE 23-21 Typical ignition switch positions. Notice the bulb check position between on (run) and start.

37. ELECTRONIC SPEEDOMETERS • Electronic dash displays ordinarily use an electric vehicle speed sensor driven by a small gear on the output shaft of the transmission. FIGURE 23-23 Permanent magnet (PM) generator vehicle speed sensor. The unit is usually driven by a gear on the output section of the transmission or transaxle.

38. ELECTRONIC ODOMETERS • A small electric motor called a stepper motor is used to turn the number wheels of a mechanical-style odometer. • A pulsed voltage is fed to this stepper motor, which moves in relation to the miles traveled. FIGURE 23-24 Some vehicles that use a PM generator for a vehicle speed sensor use a stepper motor to drive a mechanical odometer. The stepper motor receives a signal (pulses) from the vehicle computer and rotates in “steps” corresponding to the distance to the distance traveled.

39. ELECTRONIC SPEEDOMETER AND ODOMETER SERVICE • If the speedometer and odometer fail to operate, the speed sensor should be the first item checked. • If the speedometer and odometer fail to operate, the speed sensor should be the first item checked.

40. ELECTRONIC FUEL-LEVEL GAUGES • Electronic fuel-level gauges ordinarily use the same fuel tank sending unit as that used on conventional fuel gauges. • The only difference between a digital fuel level gauge and a conventional needle type is in the display. FIGURE 23-25 A typical fuel pump and fuel-level gauge module. The float moves against a resistor and changes the resistance of the circuit with the fuel level.

41. WHY DOES THE OIL PRESSURE GAUGE ON MY FORD ALWAYS READ IN THE MIDDLE? • Some Ford Motor Company vehicles (and perhaps others) use an analog oil pressure display that is set to read in the middle of the scale as long as there is a minimum oil pressure. FIGURE 23-26 (a) A Ford dash display with the key on, engine off. (b) As soon as the engine starts, the oil pressure gauge goes immediately to the midpoint on the gauge. This seems stranger to some vehicle owners.

42. WHY DOES THE OIL PRESSURE GAUGE ON MY FORD ALWAYS READ IN THE MIDDLE? • The older-style gauge used a variable-resistance oil pressure sending unit. FIGURE 23-27 A typical magnetic and pressure gauge circuit. Notice that the oil pressure gauge reading depends on the resistance of the sensor. The lower the resistance, the higher the oil pressure on most Ford vehicles.

43. WHY DOES THE OIL PRESSURE GAUGE ON MY FORD ALWAYS READ IN THE MIDDLE? • On newer models, Ford started using an oil pressure switch that electrically grounds the oil pressure gauge through a 20 ohm resistor when the oil pressure is above 4.5 to 7.5 psi. FIGURE 23-28 When the oil pressure exceeds 4.5 to 7.5 psi, the oil pressure switch closes and the meter reads in about the middle of its range due to the fixed 20 ohm resistor in the meter circuit.

44. NAVIGATION AND GPS • The global positioning system (GPS) uses 24 satellites in orbit around the earth to provide signals for navigation devices. FIGURE 23-29 Global positioning systems use 24 satellites in high earth orbit whose signals are picked up by navigation systems. The navigation system computer then calculates the location based on the position of the satellite overhead.

45. NAVIGATION AND GPSBackground • The current GPS was developed in the 1980s after a civilian airplane from Korean Airlines, Flight 007, was shot down after it had gone over Soviet territory in 1983. • Until 2000, nonmilitary use of GPS was purposely degraded by a computer program called selection availability (S/A) built into the satellite transmission signals.

46. NAVIGATION AND GPSNavigation System Parts and Operation • The navigation controller located in the rear of the vehicle uses other sensors, including a digitized map to display the location of the vehicle. • GPS satellite signals • Yaw sensor • Vehicle speed sensor • Audio output/input

47. NAVIGATION AND GPSNavigation System Parts and Operation • Navigation systems include the following components: 1. Screen display 2. GPS antenna 3. Navigation control unit that usually has a DVD with the map information FIGURE 23-30 The navigation control unit is located in the trunk of this Acura.

48. NAVIGATION AND GPSNavigation System Parts and Operation • The DVD includes street names and the following: 1. Points of interest (POI). 2. Business addresses and telephone numbers as well as hotels and restaurants. 3. Turn-by-turn directions can be provided to addresses that are selected by: • Points of interest (POI) • Typed in using a keyboard shown on the display

49. NAVIGATION AND GPSNavigation System Parts and Operation • The navigation unit then often allows the user to select the fastest way to the destination, as well as the shortest way, or how to avoid toll roads. FIGURE 23-31 A typical navigation display showing various options. Some systems do not allow access to these functions if the vehicle is in gear and/or moving.

50. NAVIGATION AND GPSDiagnosis and Service • For the correct functioning of the navigation system, three inputs are needed. • Location • Direction • Speed