1. start

10. Figure 43–2 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).

12. Figure 43–3 Many vehicles use a computer display for many 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.

14. Today’s electronic circuits are often too complex to show on a wiring diagram. Instead, all electronics are simply indicated as a solid box with “electronic module” printed on the diagram. Even if all electronic circuitry was shown on the diagram, it would require the skill of an electronics engineer to determine exactly how the circuit was designed to work. Review the circuit at right. Find Service Information and Use It Note that the grounding for the “check oil” dash indicator lamp is accomplished through an electronic buffer. The exact conditions, such as amount of time since the ignition was shut off, are unknown to the tech. To correctly diagnose problems with this type of circuit, techs must read, understand, and follow written diagnostic procedures specified by the manufacturer. Figure 43–4

16. Figure 43–5 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 43–6 The dash-mounted control for the head-up display on this Cadillac allows thedriver to move the image up and down on the windshield for best viewing. Continued

17. Figure 43–7 A typical head-up display (HUD) unit.

19. Figure 43–8 A night vision camera in the front of a Cadillac.

26. After replacing valve cover gaskets on a Chevrolet V-8, the technician discovered the oil pressure-warning lamp was on. After checking the oil level and finding everything else okay, the tech discovered a wire pinched under the valve cover. The wire went to the oil pressure sending unit. The edge of the valve cover had cut through the insulation and caused current from the oil lamp to go to ground through the engine. Normally the oil lamp comes on when the sending unit grounds the wire from the lamp. The tech freed the pinched wire and covered the cut with silicone sealant to prevent corrosion damage. Oops!

28. Figure 43–12 A Ford oil pressure-sending unit. Most oil pressure-sending units are located near the oil filter and are threaded into an oil gallery.

30. Figure 43–13 A GM temperature gauge showing normal operating temperature between 180° and 215°F, depending on the specific vehicle and engine.

32. Figure 43–15 Typical brake warning light switch located on or near the master brake cylinder. 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. Continued

45. Figure 43–19 (a) View of the vehicle dash with the instrument cluster removed. Sometimes the dash instruments can be serviced by removing the padded dash cover (crash pad) 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. Continued (a) (b) (c)

48. Many ignition switches have six positions, shown here. Notice the bulb test position—between “on” and “start.” The Bulb Test - Part 1 Figure 43–21 Many newer vehicles place the ignition switch on the dash and incorporate antitheft controls. Note the location of the accessory position. Figure 43–20 Typical ignition switch positions. Notice the bulb check position between ON (RUN) and START. Technicians often use this ignition switch position to check operation of fuses that protect various circuits.

49. When the ignition is “on” (run), some dash warning lamps are illuminated. When the bulb test position is reached, additional dash warning lamps often are lighted. Dash warning lamps are not all powered by the same fuses. If an electrical component or circuit does not work, the power side (fuse) can be quickly checked by observing the operation of the dash lamps that share a common fuse with the problem circuit. Consult a wiring diagram for fuse information on the exact circuit being tested. The Bulb Test - Part 2

51. The owner of a Lincoln Town Car complained that all of a sudden the speedometer needle went up and down with engine speed rather than vehicle speed. In fact, the speedometer needle went up and down with engine speed even though the gear selector was in “park” and the vehicle was not moving. After hours of troubleshooting, the service technician went back and started checking the basics and discovered that the generator (alternator) had a bad diode. The tech measured over 1 volt AC and over 10 amperes of AC current using a clamp-on AC/DC ammeter. Replacing the generator restored the proper operation of the speedometer. The Speedometer Works as a Tachometer

53. Diagnosing problems with digital or electronic dash instruments can be difficult. Replacement parts generally are expensive and usually not returnable if installed in the vehicle. A popular trick that helps isolate the problem is to use a soldering gun near the PM generator. The Soldering Gun Trick - Part 1 A PM generator contains a coil of wire. As the magnet inside revolves, a voltage is produced. It is the frequency of this voltage the computer uses to calculate vehicle speed. A soldering gun plugged into 110 volts AC will provide a strong varying magnetic field around the soldering gun. This field is constantly changing at the rate of 60 cycles per second. This frequency of the magnetic field induces a voltage in the windings of the PM generator. This induced voltage at 60 hertz (Hz) is converted by the computer circuits to a miles-per-hour (mph) reading on the dash. To test the electronic speedometer, turn the ignition to “on” (engine off) and hold a soldering gun near the PM generator.

58. Figure 43–23 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 traveled. Continued

60. A tech was asked to fix the speedometer on a Pontiac Grand Am that showed approximately double the actual speed. Previous repairs had included a new vehicle speed sensor (VSS) and computer. Nothing made any difference. The customer stated the problem happened suddenly. After hours of troubleshooting, the customer happened to mention that the automatic transaxle had been repaired shortly before the speedometer problem. The root cause of the problem was discovered when the tech learned that a final drive assembly from a 4T60-E transaxle had been installed on the 3T-40 transaxle. The 4T60-E final drive assembly has 13 reluctor teeth whereas the 3T-40 has 7 teeth. This difference in number of teeth caused the speedometer to read almost double the actual vehicle speed. After the correct part was installed, the speedometer worked correctly. The tech now always asks if there has been any recent work performed before diagnosis is started. Look for Previous Repairs

63. The owner of a Dodge minivan complained that after the vehicle was cleaned inside and outside, the temperature gauge, fuel gauge, and speedometer stopped working. The vehicle speed sensor was checked and found to be supplying a square wave signal that changed with vehicle speed. A scan tool indicated a speed, yet the speedometer displayed zero all the time. Finally, the service technician checked the body computer to the right of the accelerator pedal and noticed that it had been wet—from the interior cleaning. Drying the computer did not fix the problem, but a replacement body computer fixed all the problems. The owner discovered that electronic devices do not like water and that computers cannot swim. Electronic Devices Cannot Swim

66. 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. Think of the gauge as an oil pressure switch (on or off) rather than a variable display of the actual oil pressure. The older-style gauge used a variable resistance oil pressure-sending unit. On newer models, Ford started using an oil pressure switch that electrically grounds the oil pressure gauge through a 20-ohm resistor whenever the oil pressure is above 4.5 to 7.5 PSI. To determine which type of gauge you have, ground the sending unit with the key on (engine off) and observe the gauge. If the gauge reads exactly one-half, then the vehicle has a switch-type oil pressure-sending unit. Why Does the Oil Pressure Gauge on My Ford Always Read in the Middle?

67. Figure 43–25 (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 strange to some owners. Figure 43–26 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. (a) (b) Why Does the Oil Pressure Gauge on My Ford Read in the Middle?

71. No. The navigation system uses signals from the satellites and uses the signals from three or more to determine position. If the vehicle is equipped with OnStar ® , then the vehicle position can be monitored by the use of the cellular telephone link to OnStar ® call centers. Unless the vehicle has a cellular phone connection to the outside world, the only people who will know the location of the vehicle are the persons inside the vehicle viewing the navigation screen. Does the Government Know Where I Am? Continued

78. Most vehicle navigation systems use a touch screen for use by the driver (or passenger) to input information or other on-screen prompts. Most touch screens use infrared beams projected from the top and bottom plus across the screen to form a grid. The system detects where on the screen a finger is located by the location of the beams that are cut. Do not push harder on the display if the unit does not respond or damage to the display unit may occur. If no response is detected when lightly depressing the screen, rotate the finger to cause the infrared beams to be cut. Touch Screen Tip

87. Figure 43–33 A typical view displayed on the navigation screen from the backup camera. Continued

93. Figure 43–35 A typical backup sensor display located above the rear window inside the vehicle. The warning lights are visible in the inside rearview mirror.

108. end