Automobile Inspection Technology

Chapter 19 Detection Technology of Automotive Electronic Control System (4)
Detection sensor magnetic circuit air gap
Use a non-magnetic thickness gauge to measure the air gap between the signal rotor and the magnetic head of the sensing coil, as shown in Figure 4-29(b), the size of the air gap should be 0.2-0.4mm, if the air gap does not meet the requirements, the sensor needs to be replaced Assembly.

4. Overhaul of Hall-type crankshaft and camshaft position sensors

The detection methods of various types of Hall sensors are basically the same, and the technology of the crankshaft and camshaft position sensors of Cherokee Jeep
The operation status can be tested with DRB-2 or DRB-3 special detector.If there is no special detector, a high-impedance digital multimeter can be used for detection.

(1) Detect the power supply voltage of the crankshaft position sensor
The connecting circuit of the crankshaft position sensor of a Jeep Cherokee is shown in Figure 4-30. The wiring harness plug is a three-terminal plug with three terminals A, B, and C on the plug. A is a power terminal, connected to the ECU socket terminal 7; B is a signal output terminal, connected to the ECU socket terminal 24; C is a ground terminal, connected to the ECU socket terminal 4.

Connecting lines; b) Harness plug
When the ignition switch is turned on, use a multimeter to check that the power supply voltage between terminals A and C on the plug should be 8V.If the power supply voltage is 0, turn off the ignition switch, and use a multimeter resistor OHM2000 to detect the resistance between terminal A and terminal 7 on the ECU plug. The resistance value should be less than 0.5n; if the resistance value is infinite, it means that the power supply is short-circuited. Just replace the wire; if the power supply voltage is 0V and the power line is also good, it means that the ECU is faulty and should be replaced with a new one.

Detect signal voltage of crankshaft position sensor
When the ignition start switch is turned on to start the engine, the signal voltage between the sensor terminals B and C should be constantly changing between 0.3-5.0V.A light-emitting diode (the positive pole is connected to the B terminal) and a 5100/0.25W resistor can be connected in series between the B and C segments for testing.When the engine is running, the LED should flash intermittently.If the power supply voltage is normal and the diode does not flash, it means that the sensor is faulty and should be replaced with a new one.

5. Overhaul of camshaft position sensor

(1) Detect the power supply voltage of the camshaft position sensor

The connection circuit of the camshaft position sensor of Jeep Cherokee is shown in Figure 4-31. The harness plug is a three-terminal plug with three terminals A, B, and C on the plug. A is the power terminal, connected to the ECU socket terminal 7; B is the signal output terminal, connected to the ECU socket terminal 44; C is the ground terminal, connected to the ECU socket terminal 4.The detection method of the power supply voltage is the same as that of the crankshaft position sensor.

Detect signal voltage of camshaft position sensor

When the ignition switch is turned on, the engine is started and running, the signal voltage between the sensor terminals B and C should be constantly changing between 0.3V and 5.0V.When detecting the output voltage of the sensor, remove the distribution cover, turn on the ignition switch, and turn the crankshaft. When the blade of the impulse ring enters the signal generator, the voltage between terminals B and C should be 5V; when the blade leaves the signal generator , the signal voltage between B and C terminals should be lower than 0.3V.If the voltage does not meet the requirements, it means that the sensor is faulty and should be replaced with a new one.

(a) Connection line (b) Harness plug
Figure 4-31 Connecting circuit of camshaft position sensor of Jeep Cherokee
Taste.When detecting the output voltage of the sensor, it is also possible to connect a light-emitting diode in series between the B and C terminals (the anode is connected to the B terminal) and a 510n/0.25W resistor for testing.The LED should flash when the engine is running.If the power supply voltage is normal and the diode does not flash, it means that the sensor is faulty and should be replaced with a new one.

6. Maintenance of manifold pressure sensor

The maintenance methods of various types of automobile manifold pressure sensors are similar. The following is an example of the maintenance methods of the Cherokee Jeep manifold pressure sensor.The installation position and circuit connection of the manifold pressure sensor are shown in Figure 4-32.

(1) Check the vacuum hose connection

Carefully check the connection between the map vacuum hose and the throttle body. If the connection is poor or leaks, it will affect the performance of the sensor and directly affect the engine work. Repair or replace the vacuum hose as appropriate.

(2) Detection of sensor power supply voltage
When the ignition switch is turned on, the sensor V is detected.The voltage on the terminals should be 4.5-5.5V.If the voltage is zero, then check the voltage on terminal 6 of the ECU harness plug. If the voltage is 4.5-5.5V, it means that the sensor power circuit is short-circuited or the plug is loose.

(3) Detection of sensor signal voltage
The signal voltage output by the sensor can be measured with a high-resistance digital multimeter with a DC voltage block.There are three terminals A, B and C on the sensor socket. When the ignition switch is on and the engine is not started, the voltage on the detection output terminal B should be 4-5V; Drop to 1.5-2.1V; when the throttle opening increases, the B terminal voltage should gradually increase.If the voltage on the terminal 1 of the ECU harness plug is detected, it should be the same as the voltage on the B terminal.If the test result does not meet the requirements, it means that the sensor signal line is broken, the plug is loose, or there is a fault inside the sensor.

(4) Detect the connection of the negative wire of the sensor
Use a multimeter resistor OHM200n to check that the resistance between the C terminal of the sensor and the engine block should be less than 0.5n. If the resistance is too large, it means that the negative wire of the sensor is open or the ECU is not well connected.

7. Overhaul of the throttle position sensor

When the throttle position sensor TPS breaks down, the engine ECU can detect it and make the engine run in a fault emergency state. The fault reading device can be used to read the relevant information of the fault through the diagnostic socket.

(1) Overhaul of the contact throttle position sensor

When overhauling the contact switch type TPS, a multimeter can be used to measure the output voltage of the sensor signal output terminal and the contact resistance of the contact to judge.

When detecting the output voltage, connect the sensor normally, turn on the ignition switch, the output voltage should be high level or low level, and when the throttle shaft rotates, the output voltage should change alternately (from low level "0" to High level "1" or high level "1" becomes low level "".

When testing the state of the contact, unplug the sensor harness plug, and measure the resistance of the contact should be less than 0.5n. If the resistance is too large, it means that the contact is ablated and the contact is poor, and the sensor should be repaired or replaced.

(2) Overhaul of variable resistance throttle position sensor

When detecting variable resistance TPS, use a multimeter to detect the resistance value and voltage value of the sensor for judgment.Take Toyota and Xiali sedan variable resistance throttle position sensor detection as an example to illustrate the detection method.

① Check the throttle position sensor position resistance.First unplug the sensor harness plug, and then use a multimeter to detect the resistance between the signal output terminal VTA and the ground terminal E, as shown in Figure 4-33(a).When the sensor is in the initial state (that is, the gap between the stop screw and the stop rod is zero), the resistance value should be 200-600n; when the throttle valve is fully open, the resistance value should be 1500-3000n.If the resistance value is infinite, it means that the contact between the sliding back and the coating resistance is poor, and the sensor needs to be replaced.

Detect sensor power supply terminal V.When the resistance value between the terminal E and the grounding iron terminal E is shown in Figure 4-33(b), the resistance value should be 1000-10000n.If the resistance value is infinite, it means that the coating terminal is broken and the sensor needs to be replaced.

②Check the sensor harness.When using the multimeter resistance OHM200n to detect the harness resistance, turn off the ignition, unplug the electric control unit and the sensor harness plug, and check that the resistance value of the wire between the corresponding terminals on the two plugs should be less than 5n.If the resistance value is too large or infinite, it means that the wire harness and the terminal are in poor contact or open circuit and should be repaired.

③Detect the power supply voltage and signal voltage.When testing, turn on the power switch, and use a multimeter to check that the power supply voltage of the sensor should be 5.oV.When the throttle is closed, the signal voltage of the detection sensor should be 0.5-1.oV; when the throttle opening gradually increases, the signal voltage should rise accordingly; when the throttle is fully opened, the signal voltage should be 4.0- 4.8V.If the test result does not match this, the sensor needs to be replaced.

8. The use and maintenance of the oxygen sensor EGO

(1) Use of oxygen sensor

When the car travels a certain mileage (generally 80000km), the oxygen sensor should be replaced.The main reason for the failure of the oxygen sensor is the aging and poisoning of the sensing element.

①Oxygen sensor aging.The main reason for the aging of the oxygen sensor is that the local surface temperature of the sensing element is too high.During the closed-loop control process of the engine using the oxygen sensor, the air-fuel ratio of the mixture is always controlled near the theoretical air-fuel ratio, and there is no excess fuel in the exhaust, but after the engine has just started (especially cold start) (or heavy load state When working), in order to speed up the warm-up of the engine (or increase the engine output power), it is necessary to supply enough fuel, and the excess fuel in the exhaust gas will produce a combustion reaction on the surface of the oxygen sensor. On the one hand, it will form carbon particles and cause the oxygen sensor The protective layer on the surface peels off; on the other hand, the local surface temperature of the sensor element is too high (exceeding 1000-C) to accelerate the aging of the sensor.

② Oxygen sensor poisoning.The phenomenon that the sensing element of the oxygen sensor is polluted and fails is called poisoning.The poisoning of the oxygen sensor mainly refers to lead (Pb) poisoning, silicon (Si) poisoning and phosphorus (P) poisoning.

a. Lead poisoning.Lead ions in fuel or lubricating oil additives chemically react with the platinum electrode of the oxygen sensor, resulting in a decrease in the catalytic performance of the catalyst platinum, which is called lead poisoning.

The test proves that the zirconia sensor will be seriously poisoned after driving 1.8km under the condition of 480g lead per liter of gasoline or 0.15km under the condition of 1000g lead per liter of gasoline.Since tetraethyl lead is added to leaded gasoline to improve gasoline octane number and anti-knock performance, cars equipped with zirconia oxygen sensors and three-way catalysts are prohibited from using leaded gasoline.In addition, since various lead compounds are contained in fuel or lubricating oil additives, lead poisoning is also inevitable.

Ways to improve the lead resistance of the oxygen sensor: one is to use a heated zirconia oxygen sensor.Experiments have shown that the lower the temperature, the more serious the lead poisoning, because lead is a solid particle under low temperature conditions, which is easy to precipitate on the surface of the sensor and cause the sensor to fail.At high temperature, most of the lead is a gas and it is difficult to pass through the sensing element.The second is to use a titanium oxide oxygen sensor with variable resistance.Although the titanium oxide oxygen sensor also uses metal platinum as the electrode, it is only for electrical connection, and its performance will not be affected even if it is polluted by lead ions.

b. Silicon poisoning.The chemical reaction between silicon ions and the platinum electrode of the oxygen sensor leads to the reduction of the catalytic performance of the catalyst platinum, which is called silicon poisoning.

The silicon sealant on the engine, the silicone resin molding parts, and the silicon additives in the casting all contain silicon ions, which will contaminate the outer electrodes of the oxygen sensor, and the silicone rubber used for sealing the internal terminals of the oxygen sensor will contaminate the inner electrodes.Since the titania oxygen sensor does not have an inner electrode, and the outer platinum electrode is only for electrical connection, the degree of silicon poisoning is much lighter than that of the zirconia sensor.

It can be seen that whether it is a zirconia oxygen sensor or a titanium oxide oxygen sensor, aging and poisoning of the sensing element are inevitable.Therefore, when the car travels a certain mileage (generally 80000km), the oxygen sensor should be replaced.When replacing the oxygen sensor, be sure to brush the oxygen sensor mounting thread with a special anti-sticky fluid, otherwise it will be difficult to disassemble in the next maintenance.When brushing the anti-stick fluid, do not apply it to the vent hole of the oxygen sensor.In terms of the anti-pollution ability and anti-aging of the oxidation sensor, the titanium oxide type is better than the heating type zirconia type, and the heating type zirconia type is better than the non-heating type zirconia type. Therefore, the development prospect of the titanium oxide type oxygen sensor is very broad.

The maintenance of the oxygen sensor is mainly to check whether the heating element and the signal voltage change frequency are normal.When detecting the frequency of oxygen sensor signal voltage changes, the interval between high and low levels should not be lower than 10 times/min.

(2) Overhaul of oxygen sensors for Santana and Jetta cars

① Check the heating element resistance.The position of each terminal on the oxygen sensor connector plug and socket of Santana 2000GSi, 3000, Jetta AT, and GTX cars is shown in Figure 4-34.

The resistance value of the heating element is 1-5n at normal temperature, and when the temperature rises little, the resistance value will increase significantly.Therefore, at room temperature, a multimeter can be used for measurement.When testing, unplug the oxygen sensor harness plug, and the resistance between terminals 1 and 1 on the testing plug should be 5-[-]n at normal temperature.If the resistance value is infinite at room temperature, it means that the heating element is broken and the oxygen sensor should be replaced.

②Check the oxygen sensor voltage.The voltage of the heating element of the oxygen sensor is the power supply voltage of the whole vehicle. When the ignition switch is turned on and the fuel pump relay contact is turned on, the power supply of the heating element is turned on.When testing the voltage of the heating element, unplug the oxygen sensor, start the engine, and check that the voltage between terminals 1 and 11 on the connector socket should not be lower than 2000V.If the voltage is zero, it means that the fuse (Santana 3000Gsi, 30 type additional fuse, 18A; Jetta AT, GTX No. 20 fuse, [-]A) is open or the contact of the fuel pump relay is in poor contact, and they can be repaired separately.

To detect the signal voltage of the oxygen sensor, a light-emitting diode and a 510n/0.25W resistor can be connected in series between the sensor 3 and the wire connected to the terminal for testing.The anode of the diode is connected to the 4-terminal wire, and the cathode of the diode is connected to the 300-terminal wire of the connector through a 3n resistor.When the engine is idling or running at part load, the LED should be flashing.If the power supply voltage is normal and the diode does not flash, it means that the sensor is faulty and should be replaced with a new one.The light-emitting diodes should flash no less than 10 times/min.If the diode does not flash or the flashing frequency is too low, it means that the heating element of the oxygen sensor is invalid, the air hole on the oxygen sensor housing is blocked, the thermal load of the oxygen sensor is too heavy or long-term use of leaded gasoline will cause the oxygen sensor to fail, and the sensor needs to be replaced.

9. Maintenance of temperature sensor

The temperature sensor is a correction symbol for many control functions, such as the coolant temperature sensor signal is used for fuel injection quantity correction, ignition advance angle correction, activated carbon cylinder tank solenoid valve control, etc.If the signal of the coolant temperature sensor is interrupted, it will lead to difficulties in cold starting of the engine, increased fuel consumption, reduced idle speed stability, and increased exhaust emissions.Although the resistance values ​​of the temperature sensors used in various types of vehicles are different, their maintenance methods are basically the same.

(1) Detection of power supply voltage and signal voltage
When detecting the coolant temperature sensor, a high-impedance digital multimeter can be used to detect the power supply voltage and signal voltage of the sensor on the vehicle.When detecting the power supply voltage, unplug the coolant temperature sensor, turn on the ignition switch, and check the sensor harness
The power supply voltage between the two terminals on the plug should be about 5V.

When detecting the signal voltage, plug in the sensor plug, turn on the ignition switch, and the detection signal voltage should meet the standard value.When the engine temperature is high, the signal voltage is low; when the temperature is low, the signal voltage is high.If the voltage deviates too much from the standard value, the sensor should be replaced with a new one.

When detecting the resistance value of the thermistor and detecting the resistance value of the temperature sensor, disconnect the ignition switch, pull out the temperature sensor plug under Figure 4-35 Temperature Sensor Maintenance Method, remove the temperature sensor, and insert the sensor
Put the thermometer and thermometer in a beaker or heating container, as shown in Figure 4-35.In the case of different temperatures, use a multimeter to detect the resistance value between the two terminals on the sensor socket, and then compare it with the standard resistance value.The standard resistance values ​​of the temperature sensors of different models are different. The standard resistance values ​​of the temperature sensors of Toyota vehicles are shown in Table 4-6.If the resistance deviation is too large, too small or infinite, it means that the temperature sensor is invalid and should be replaced with a new one.

(3) Overhaul of Santana car coolant temperature sensor

桑塔纳2000GSi、3000型轿车电控系统用冷却液温度传感器G62与仪表系统的冷却液温度传感器G2-起组装在一个缸体内，安装在汽缸盖后端的出水管上，如图4-36所示。传感器插座上有四个接线端子，G62连接1、3端子，G2连接2、端子。信号输出端子3与电控单元J220插座上的端子53连接，传感器负极端子1与电控单元J220插座上的传感器搭铁端子67连接。

When detecting the resistance value of the coolant temperature sensor of Santana 2000GSi and 3000 cars, connect the two meters of the multimeter to the signal output on the sensor socket and the ground terminal of the sensor respectively.When the temperature is 30°C, the resistance should be 1500-2000n; when the temperature is 80°C, the resistance should be 275-375n.If the resistance value deviation is too large, too small or infinite, it means that the sensor is invalid and should be replaced with a new one.

(4) Overhaul of intake air temperature sensor of Santana 2000Gsi and 3000 cars

(End of this chapter)