Car body electrical practice

1. Battery; 2. Ignition lock; 3. Fuel gauge; 4. Sensor

fuel level

- Check the operation of the fuel level display

+ Remove the fuel level sensor connector. Turn the ignition switch to 0N and check that the gauge needle is in the EMPTY position.

+ Install a 3.4W light bulb between terminal 1 and (-) of the battery. Make sure the light is on and the meter is working. Note: Because there is Silicon oil in the meter, it takes about 90s for the needle to be in a balanced state.

If the watch does not work, remove and inspect the watch.

- Measure the resistance of the AB meter: approximately 102Ω

AC: approx. 101Ω BC: approx. 203 Ω

If each resistance value is not as above, replace the meter.

- Measure the resistance value of the fuel level sensor

+ Make sure the resistance changes as the fuel float moves.

- Measure the resistance value between terminal 1 and the sensor housing

Fuel float position (mm)

Resistor
F	64.7-70.7	0.9-5.1Ω
1/2	153	29.7-37.3 Ω
E	205.5-211.5	100.3-117.7 Ω

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If the resistance value is not as per the table above, replace the sensor.

- Check the low fuel warning light

+ Remove the fuel level sensor connector. Connect terminal 1 to the sensor housing.

+ Turn the ignition On, make sure the light is on, if not, remove and check the indicator light bulb

2. Check the fuel level switch

- Apply battery voltage between terminals 2 and 3 through a 3.4 W light bulb. Make sure the light is on.

- Put the switch in gasoline or water. Make sure the light is off.

If not lit replace sensor

2.2. Water temperature alarm circuit

2.2.1. Circuit diagram

The water temperature sensor is usually located on the engine body. The water temperature gauge is divided into two temperature ranges. The blue range means the cooling system is normal, and the red range indicates that the engine temperature is overheating.

Figure 4.4 Water temperature indicator circuit diagram

1. Water temperature sensor; 2. Water temperature gauge

2.2.2. Symptoms and suspected areas

Symptom

Suspicious area

The watch does not show the water temperature.

- Broken watch

- Broken wire

- Water temperature sensor broken

Water temperature gauge is wrong

- The watch is broken

- Broken temperature sensor

2.2.3. Sequence of disassembly, inspection and repair

1. Check the operation of the water temperature display

- Remove the water temperature sensor connector.

Turn on the ignition 0N and check that the gauge shows the water temperature.

1. Electric lock; 2. Water temperature gauge,

3. Water temperature sensor

1. Electric lock; 2. Water temperature gauge,

3. Test light

2.3. Lubricating oil pressure alarm circuit

- Install a 3.4W light bulb between the meter terminal and (-) battery.

- Turn the ignition switch to the ON position, make sure the light is on and the gauge needle is in the HOT position.

If not according to standard, re-measure the resistance value of the meter.

2. Measure the resistance of the meter. Example

Measurement location

Resistance value (Ω)
AB	Approximately 54
AC	Approximately 147.1
BC	Approximately 201.1

Attention:

When the test lead is connected, the ohmmeter current can rotate the clock hand.

If the resistance is not as shown in the table above, replace the meter.

The lubricating oil pressure indicator can be displayed by a gauge to know the exact lubricating oil pressure in the engine or an oil warning light (most engines now use this method).

When the engine is not running, the oil indicator light must be on. When the engine is running, the oil indicator light must be off. If the oil indicator light is still on, the engine must be stopped immediately to check the technical condition of the engine.

2.3.1. Circuit diagram

Figure 4.5 Oil pressure warning circuit diagram

1. Ignition lock; 2. Oil indicator light;

3. Oil pressure sensor

2.3.2. Symptoms and suspected areas

Symptom

Suspicious area

Oil indicator light is always on when the key is turned On and the engine is running.

- The light is shorted.

- Damaged oil sensor

- Lubrication system failure

Oil indicator light always turns off when the ignition is turned On

- Broken wire

- Sensor is broken

2.3.3. Sequence of disassembly, inspection and repair

1. Check the oil warning light

- Remove the oil sensor connector

- Connect a light bulb to the switch as shown in the picture.

- Turn the ignition On, make sure the light is on. If the light does not come on, replace the bulb.

2. Check the sensor

- Remove the connector

- Use ohmmeter to measure the switch

+ In free state, resistance must be >10 Ω

+ When a force is applied to the sensor, the resistance < 1 Ω If the operation is not as above, replace the sensor.

2.4. Engine speed and vehicle speed indicator circuit

2.4.1. Circuit diagram

Figure 4.5. Circuit diagram showing engine and vehicle speed of gasoline engine

1. Battery; 2. Electric lock; 3. Ignition coil; 4. Ignition IC; 5. Engine speedometer;

6. Vehicle speedometer; 7. Vehicle speed sensor

The signal sent back to display the engine speed for gasoline engines is the signal of the ignition IC (EXT pole) and for Diesel engines using high pressure pump VE is the sensor.

engine speed on the high pressure pump. With older vehicles, the engine speed signal was taken from the ignition coil and had a separate device to display the engine speed. Today, the ignition signal is not sent directly to the clock but is received by the ECU and the ECU will send this signal to the engine speedometer via the CAN network.

There are two types of vehicle speed sensors: mechanical and electrical. The mechanical type uses a twisted cable taken from the gearbox. The electrical type usually uses a Hall sensor placed in the gearbox or axle.

For vehicles without ABS, the vehicle speed signal sent to the clock is taken from the vehicle speed sensor.

For vehicles with ABS, the vehicle speed signal is taken from the brake actuator via the CAN communication system. For this type, a diagnostic machine must be used to check.

2.4.2. Symptoms and suspected areas

Symptom

Suspicious area
- Engine speedometer does not display	- Loss of positive or negative power to the clock - Loss of engine speed signal to the clock
- Engine speedometer is wrong	- The watch is damaged
- Vehicle speedometer does not display	- Loss of positive or negative power to the clock - Loss of engine speed signal to the clock - Broken twisted cable
- The car speedometer is wrong.	- The watch is damaged - Sensors, wires

2.4.3. Sequence of disassembly, inspection and repair

This section presents the method of disassembling and checking the speed sensor on a vehicle equipped with an automatic transmission of the Toyota Vios.

1. Disassembly sequence

-Remove the battery

-Remove the sensor connection wire clamp

-Remove battery rack

-Remove speed sensor

+ NT speed sensor jack tower.

+ Remove the bolt and NT speed sensor.

2. Testing sequence

Vehicle speed sensor jack

3. Installation sequence

+Remove the O-ring from the sensor

Use an ohmmeter to measure the resistance of the sensor.

Measurement location

Condition	Standard
1 - 2	20°C (68°F)	560 to 680 kΩ

If the result is not as specified, replace the sensor.

- Apply automatic transmission oil to the new O-ring, and install it on the sensor.

-Install speed sensor. Torque: 5.4 N*m

- Install sensor jack

-Install battery rack, wire clamps and battery

- Check for oil leaks

2.5. Built-in clock

2.5.1. Circuit diagram

Conventional display gauges take information directly from sensors (voltage signals). Today, for vehicles using CAN communication lines, the sensors will send signals to the ECU and the ECU will communicate with the integrated gauge to display the necessary information. For this type of gauge, a diagnostic machine must be used to check the technical condition of the information system.

The signals used by the CAN network are:

TACH of engine speed, THWO of water temperature sensor, SPD of vehicle speed sensor…..

Figure 4.6 Internal circuit diagram of the integrated clock without CAN network

2.5.2. Symptoms and suspected areas

Symptom

Suspicious area
- The indicator lights do not light up when the ignition is turned on.	- Power supply - Light bulb - Conductor
- The clock light bulb does not light up.	- Light bulb - Contact position of the jacks
- Information signals are lost	- Sensor - Conductor - Display details

The table above only shows some typical cases of symptoms of the car's information display. If one of the information on the dashboard does not display, there are usually two main causes: the power circuit and the sensor circuit. The sequence is as follows:

- Read the drawing to determine if any circuits share the same power source as the damaged circuit. If that circuit is still working, it can be inferred that the light bulb of the circuit being tested is damaged. If the circuits sharing the power source do not work, the most likely cause is a loss of positive or negative power to the shared circuits. If the power source is good, then it is damaged.

in the circuit will be the signal circuit.

2.5.3. Sequence of disassembly, inspection and replacement

1. Disassembly sequence

- Remove negative battery cable