Automobile Inspection Technology

Chapter 18 Detection Technology of Automotive Electronic Control System (3)
②Transmission computer fault code (A/T).The fault codes of the transmission computer can be read out by connecting the indicator light to the No. 6 terminal of the OBDH diagnostic seat and blinking.

③ABS computer fault code. The ABS computer fault code can be read out by connecting the display lamp to the No. 8 terminal of the OBDH diagnostic socket and blinking the jumper lamp.

④SRS computer fault code. The SRS computer fault code can be read out by connecting the display light to the No. 12 terminal of the OBDn diagnostic socket and blinking the jump light.

⑤ Computer fault codes for cruise control (C/C).Constant speed (C/C) computer fault codes can be read out by connecting the indicator light to the No.

(8) The method of clearing the fault code: as long as the negative ground wire of the battery is removed for more than 15 seconds, the fault code can be cleared (except the ABS fault code).

The way to clear the ABS fault codes of Mitsubishi cars is to have a plug with two ends behind the cigarette lighter, which are red/yellow and green/white wires. These two wires are respectively connected to terminals 9 and 10 of the ABS computer.

Figure 4-20 Basic procedure for fault diagnosis of engine electronic control system

①Connect the above two wire ends, turn on the ignition switch, at this time, the ABS solenoid valve is fully closed, and the indicator light flashes.

②Wait for more than 7s to turn off the ignition switch and disconnect the jumper wire.

③Turn the ignition switch ON again to clear the ABS fault code.

[-]. Basic procedure of fault diagnosis

The fault diagnosis of automotive electronic control system should be carried out step by step on the basis of mastering the basic principles and basic ideas of fault diagnosis.The correct detection procedure is a guide to quickly find the fault content, which can effectively prevent missed diagnosis and misdiagnosis.When diagnosing the fault, it should be carried out in six steps, namely, asking the user about the relevant situation, visual inspection, basic inspection, self-diagnosis test, difficult fault diagnosis and component maintenance, etc.It is applicable to various types of electronic control systems, and it is also applicable to certain electronic control systems of different structures and forms, only the content of the basic inspection is different.Taking the engine electronic control system as an example, the basic procedure of fault diagnosis of the electronic control system is shown in Figure 4-20.

(Section [-]) Inspection of Electronically Controlled Fuel Injection System

[-]. Fuel pressure test

The fuel system failure can be accurately judged through the fuel system pressure test. The oil pressure of the engine system is different for different car series, different injection types, and different displacements, see Table 4-3.The connection between the fuel pressure gauge and the fuel pipe of different car series is also different. Some engines have a pressure test hole at one end of the fuel distribution pipe. Just connect the fuel pressure gauge to the test hole according to the steps.For engines without pressure test holes, you need to select a suitable pipe joint to connect the oil pressure gauge to the fuel pipeline.Take the 3VZ-FE engine equipped with Toyota Camry as an example.

1. Release system fuel pressure
The battery voltage is not lower than 12V, unplug the electric fuel pump relay (or fuel pump power plug), start the engine, wait for the engine to automatically turn off, then start the engine 2-3 times, turn off the ignition switch, and install the electric fuel pump relay (or fuel pump power plug).

2. Install the fuel pressure gauge

Turn the ignition switch to the LOCK position, remove the cable from the negative terminal of the battery for 30 seconds, unplug the connector of the cold starter, put a container or cloth under the oil pipe of the cold start fuel injector, and remove the cold start fuel injector Oil pipes and gaskets on the device, as shown in Figure 4-21.Connect the pressure gauge to the cold start fuel injector with a new gasket and fuel pipe joint bolts, and connect to the fuel pressure gauge (pay attention to the measurement joint and position), as shown in Figure 4-22.Use a jumper wire to bridge the +B and Fp terminals of the diagnostic socket, and reconnect the battery negative cable as shown in Figure 4-23.

3. Static fuel pressure detection

Turn on the ignition switch (do not run the engine), observe the oil pressure value on the gauge, the specified fuel pressure is 264-304kPa, if the pressure is low, check the fuel pipe, fuel pipe joint, fuel pump, fuel filter, fuel pressure regulator and Are there any leaks in the fuel injector, etc.?

4. Dynamic pressure detection

Start the engine, remove the vacuum tube from the fuel pressure regulator, and block the tube opening, measure the fuel pressure at idle speed, and the fuel pressure is 264-304kPa.Connect the vacuum tube to the fuel pressure regulator again, measure the fuel pressure at idle speed, the fuel pressure is 225-265kPa.If the pressure is not as specified, check the vacuum line and fuel pressure regulator.

5. Fuel system maintains pressure detection

Turn off the engine, check the fuel pressure after 5 minutes, it should not be lower than 147kPa.If the pressure does not meet the above regulations, check the fuel pump, pressure regulator and fuel injector, etc.After the inspection, remove the battery negative cable and fuel pressure gauge, reinstall the cold start fuel injector with new gaskets and oil pipe joint bolts, plug in the connecting wire, reconnect the battery negative cable, and check for fuel leakage .

[-]. Fuel pump test
When testing the fuel pump, make sure that the battery voltage is normal, the fuel pump fuse is normal, and the fuel filter is normal.

1. Fuel pump circuit inspection

①Turn on the ignition switch, you should hear the sound of the fuel pump starting, and you should feel the oil pressure if you pinch the fuel pipe with your fingers.

②If the fuel pump does not start, check the fuel pump, fuel pump relay and fuel pump control circuit.

③When the ignition switch is set to "ON", the fuel pump relay must have an action sound, otherwise check the circuit of the fuel pump relay, if normal, replace the fuel pump relay.

④ If the fuel pump relay is good but the fuel pump still does not work, measure the power supply voltage on the fuel pump with a multimeter when the ignition switch is set to "ON". The rated value of the voltage is about the voltage of the battery (about 12V).If the rated voltage value is not reached, check and eliminate the short-circuit fault in the circuit according to the circuit diagram; if the rated voltage value is reached, and the ground wire at the fuel pump is not short-circuited, it means that the fuel pump is faulty, and the fuel should be inspected and replaced. Pump.

2. Inspection of fuel pump

① Turn the ignition switch to "OFF", and disconnect the electrical plug of the fuel pump.

② Measure the resistance of the fuel pump coil with a resistance meter, if it is not within the specified range, replace the fuel pump assembly.

③Add 12V power supply to the fuel pump (note the polarity), and check the operation of the fuel pump.If abnormal, replace the fuel pump assembly. (Note: This experiment should be completed within 10 seconds to avoid burning out the fuel pump coil, and keep the fuel pump away from the battery at the same time)

3. Measure the fuel supply of the fuel pump

①Turn off the ignition switch.

② After the pressure is released, connect the oil pressure gauge to the oil delivery pipe.Attach the hose back to the oil line and into the measuring cup.

③Use the plug wire to short-circuit the contact of the fuel pump relay and the positive terminal of the battery, make the fuel pump run and build up the oil pressure of the system, and then cut off the power.

④ Empty the measuring cup.

⑤ Connect the fuel pump to make it run.Measure the pump oil volume within the specified time and compare it with the specified value.If the minimum fuel delivery rate is not reached, the cause of the failure may be a bent or blocked fuel delivery pipe, blocked fuel filter, fuel pump failure, etc.

[-]. Inspection of fuel injector

1. Inspection of fuel injector

(1) Inspection of the working condition of the fuel injector

When the engine is running, touch the fuel injector with your hand or use a stethoscope to check whether the fuel injector works and whether its working condition matches the engine speed.If abnormal, check the fuel injection signal output by the fuel injector or ECU.

If the fuel injector is difficult to access, it can be checked by disconnecting the fire.The action should be fast when checking, otherwise the long-term broken cylinder will shorten the service life of the three-way catalytic converter.

(2) Check whether the fuel injector is blocked
① Turn the ignition switch to "OFF", and disconnect the electric plugs of all fuel injectors.

②Install an oil pressure gauge on the oil road, start a taxi or short-circuit the power supply of the oil pressure pump to run the fuel pump and build up the oil pressure.

③ Supply 12V voltage to the pulse injectors one by one, and listen to whether the sound is normal at the same time.

Note: If it is a low-resistance fuel injector, connect a resistor with a resistance value of about 10n in series in the circuit to ensure that the coil resistance of the fuel injector is normal.

④ When power is supplied to the fuel injector, the oil pressure of the system should drop, otherwise it means that the fuel injector is dirty and blocked.

⑤If the fuel injector does not inject fuel and the oil pressure of the system drops, it means that there is leakage at the fuel injector.

⑥Remove all the fuel injectors and observe, there are black marks on the nozzle holes of the leaking fuel injectors.

(3) Inspection of fuel injector coil resistance

Turn the ignition switch to "OFF", disconnect the electric plug of the fuel injector, measure the resistance of the fuel injector coil, if it exceeds the technical range, replace it.

(4) Inspection of fuel injection quantity, atomization and leakage

You can use the injector test bench to test the above contents according to the operation steps in the instruction manual.If there is no fuel injector test bench, the following method can be used.

①Remove the fuel distribution pipe and the fuel injector together, connect the inlet of the fuel distribution pipe with the outlet of the fuel filter reliably with a hose, and connect another hose to the oil return port of the oil pressure regulator with oil return pipe.

②Set the ignition switch to "ON", short-circuit the electric fuel pump to make it run, and establish the system oil pressure.

③ Check the injector for oil leakage.The amount of oil leakage should not exceed one drop every 2 minutes, otherwise the injector should be replaced.

④ Turn the ignition switch to "OFF", and disconnect the electric plug of the fuel injector.

⑤ Place the fuel injector on a higher measuring cylinder, supply 12V voltage to the fuel injector for 15S (note: the power supply current should not exceed 1A), observe the atomization of the fuel injection, and measure and record the fuel injection volume at the same time.Repeat 2-3 times for each injector.

⑥ The standard fuel injection volume and the error between each fuel injector should meet the requirements, otherwise the fuel injector should be replaced.If the fuel injection quantity is greater or less than the specified value, the system oil pressure should be checked.

2. Check the circuit of the injector

(1) Check the power supply

① Turn the ignition switch to "OFF", and disconnect the electric plug of the fuel injector.

②Set the ignition switch to "ON", ground the negative pen of the voltmeter, and measure the two terminals of the wiring harness electrical plug successively with the positive pen. One of the terminals should have a voltage of 12V, otherwise check the ignition relay and the connection between it and the battery. Harness connection condition.

(2) Check the control terminal of the computer
The fuel injector is a pulsed power device. In order to avoid damage to the electronic circuit in the ECU, a special ground pin is provided on the ECU connector to form a self-circuit.Therefore, also check whether the fuel injector ground in the ECU is in good condition.

① Make a self-made LED display lamp with a resistance of about 330n in series.When the ignition switch is set to "OFF", connect the positive pole of the LED display light to the positive pole of the battery, and the negative pole to the computer control terminal of the electrical plug of the wiring harness, as shown in Figure 4-24.

② Turn on the starter, the LED light should flash.Otherwise, check the circuit and connection between the control terminal of the fuel injector electrical plug and the ECU.

③ If the LED lights on the electrical plugs of all cylinder fuel injectors are off, check the input signals of sensors related to fuel injection control (such as crankshaft and camshaft position sensors).

④ If the LED lights are not on when inspecting some fuel injectors, check the power transistor in the control computer ECU after checking the connection of the control terminal of the fuel injector. (An experiment can be done here to judge whether there is a fuel injection signal: remove the wire from the fuel injector control terminal to the ECU, and artificially pulse the ground to make the fuel injector inject fuel; If the injector does not inject fuel, it means that the ECU does not output fuel injection signal.)
⑤Remove the ECU, open the cover and check whether the transistor is working normally.

⑥ If the transistor is good, it means that the ECU is faulty.

Fourth, the detection of ECU

Usually use a special tester or a general-purpose diagnostic instrument to check the ECU and its control circuit faults, which can quickly and accurately find out where the fault is.If these instruments are not available, a multimeter can also be used for diagnosis.

Check the ECU with a multimeter.Use a multimeter to measure the voltage or working resistance of each pin on the socket on one side of the electronic control unit, and judge whether the electronic control unit and its control circuit are faulty or not.At this time, the detailed maintenance technical data of the inspected vehicle must be used as the basis, including: which devices are connected to each pin on the socket on one side of the electronic control unit; the standard voltage value of each pin under different working conditions of the engine, etc.If abnormalities are found during detection, it indicates that there is a fault.If the part connected to the actuator is abnormal, it indicates that the electronic control unit is faulty; if the part connected to the sensor is abnormal, the sensor or circuit may be faulty.

When testing, first remove the electronic control unit together with its wire harness from the vehicle, do not remove the wire harness plug, and insert the voltmeter test pen in turn from the side of the wire at the rear of the wire harness plug to make it contact with the back of the pin , in order to measure its voltage.To measure resistance, the harness connector should be removed.Comparing the measurement results with the standard values ​​respectively can determine where the fault lies.

[-]. Detection of sensors

The maintenance of the failure of the automotive electronic control system is mainly to repair the wiring harness, parts and connectors.Sensors are the information source of various electronic control systems, once the sensor fails, the control system cannot work normally.The maintenance methods of various sensors are different. The maintenance methods of several typical sensors are introduced below:
1. Maintenance of eddy current air flow sensor

The air flow sensor is not only a precision component, but also the most important component of the electronic control system.When the voltage regulator fails, the ECU cannot receive the correct signal of intake air volume to control the fuel injection volume, and the mixture will pass through the various types of vortex flow sensors. The maintenance methods of various types of vortex flow sensors are basically the same. The 400UZ-FE engine and the 1M-GE engine of the Crown 3.0 sedan are equipped with photoelectric detection eddy current air sensors as examples.

rich or too lean, causing the engine to run erratically.

When overhauling or disassembling the air flow sensor, it should be shown carefully. The overhaul method is as follows:
(1) Static detection

Unplug the air flow sensor harness plug, and use a multimeter to measure the resistance of the intake air temperature sensor between terminals THA and E2 on the sensor plug, as shown in Figure 4-26. The test results should be consistent. If the resistance value does not match, it needs to be replaced. sensor.

(2) Dynamic detection

Insert the sensor harness plug into the socket, and use a multimeter to measure the voltage between THA and E2, VC and Ei, and Ks and Ei of the sensor connector terminals, which should meet the requirements in Table 4-4.If the test result does not match the standard voltage value, check whether the wire harness between the sensor and the ECU is disconnected; if the wire harness is good, unplug the sensor plug and connect the point
Fire switch, detect the voltage between power supply terminal Vc and pin and signal input terminal Ks and pin, if both are 4.5-5.5V, it means that the ECU is working normally, and the flow sensor should be replaced, if the voltage is not 4.5-5.5V, it means The ECU is faulty, and the ECU should be checked or replaced.

2. Maintenance of hot wire and hot film flow sensors

The flow detection methods of various hot-wire and hot-film air sensors are basically the same. Now take the hot-film air flow sensors for Santana and Jetta cars and the hot-wire air sensors for Nissan Maxima cars as examples to illustrate their maintenance methods.

(1) Detection of sensor power supply voltage
When detecting the power supply voltage, unplug the harness plug of the sensor, turn on the ignition switch, and use a multimeter to detect the voltage between the power terminal and the ground terminal on the sensor plug with DC voltage.

When detecting the power supply voltage of the air flow sensor of Santana and Jetta cars, unplug the 5-terminal harness plug on the sensor (note: the terminal code-named 1 is a spare terminal, and there is no wire connected), as shown in Figure 4-27, and then connect Ignition switch, detect the voltage between terminal 2 on the wiring harness connector and the engine cylinder block: the specified value should not be lower than 11.5V.If the voltage is zero, it means that the contacts of the fuel pump relay may not be disconnected from the power supply line, and the fuel pump relay or power supply line needs to be overhauled.

Detect the signal voltage of the sensor

When detecting the signal voltage, unplug the sensor harness plug, connect the positive and negative poles of the battery to the power terminal and the ground terminal on the sensor plug respectively, and measure the voltage at the signal output terminal with a multimeter DC voltage; when blowing air into the air inlet of the sensor, The signal voltage should increase accordingly.

The method for testing the hot wire air flow sensor used in the VG30E engine of Nissan Maxima is: connect the positive pole of the battery to the power terminal E on the plug, and connect the negative pole of the battery to the ground terminal D on the socket, as shown in Figure 4-28. When measuring the signal voltage between the signal output terminal B and the D terminal with a multimeter, it should be 1.6V±0.5V; voltage rises to .If the signal voltage does not change, it means that the sensor is invalid and should be replaced with a new one.

(3) Check the self-cleaning function of the hot wire flow sensor on the car
Firstly plug the wire harness plug of the air flow sensor into the socket, then start the engine and increase the speed to above 2500r/min, and then make the engine idle.Remove the intake pipe at one end of the air inlet of the air flow sensor, disconnect the ignition switch, and at the same time observe from the air inlet of the sensor whether the hot wire is red and hot after the engine is turned off for 58 hours and lasts for Is.Note, however, that hot film and hot wire flow sensors that maintain a temperature above 200°C do not have this function.

3. Overhaul of magnetic induction crankshaft and camshaft position sensors

The detection methods of various types of magnetic induction sensors are basically the same. The maintenance methods of magnetic induction crankshaft and camshaft position sensors adopted by Toyota Computer Control System (TCCS) are as follows:
(1) Detection sensor coil resistance value

Unplug the sensor harness plug, the arrangement of the terminals on the socket is shown in Figure 4-29(a).Use the multimeter resistance OHM off 200n to detect the resistance value between each terminal, which should meet the requirements in Table 4-5. If the resistance value does not meet the requirements, replace the sensor assembly.

Detection coil resistance; b) detection signal generator air gap
(End of this chapter)