How to unlock Santana
A 2009 Shanghai Volkswagen Santana Zhijun sedan with a mileage of 55,000 kilometers, 1.8 liter BKT engine and a five-speed manual transmission. According to the owner, after routine maintenance more than a month ago, the car can only be started several times every morning, and it will automatically turn off after starting. When starting again, the engine can start smoothly, but when idling, the engine will stop automatically by lightly stepping on the accelerator. If the engine is started and kept running for a few minutes, and then the accelerator pedal is pressed, the engine will not shut down and the fault indicator light on the dashboard will light up.
Fault diagnosis and troubleshooting
After picking up the car, we started the engine, feeling that the engine neither ignited nor injected fuel during the starting process. We suspect that there is something wrong with the crankshaft position sensor. Connect the scan tool KT300 and read the engine starting speed 196 rpm, indicating that there is nothing wrong with the crankshaft position sensor. Read out the fault code of the vehicle engine control unit again. There are seven fault codes. After clearing the fault codes, read them again, and there are still seven fault codes, namely P0203, P0202, P020 1, P0444, P0204, P0030 and P0036, as shown in figure 1.
According to the meaning of the fault code, we first check the fuse and relay of the injector, as shown in Figure 2. It is found that the fuse and relay of the injector are normal. Unplug the fuel injector plugs, turn the ignition switch to the "on" position, and measure the power supply voltage on each plug with a multimeter, which is 12V. Turn off the ignition switch, and then measure the resistance between the control line of each fuel injector plug and the ground with a multimeter resistance file.
The measurement method is as follows: firstly, connect the control terminal of the fuel injector plug to the red probe of the multimeter, and connect the black probe to the body ground with infinite resistance; Then connect the control end of the fuel injector plug to the black probe of the multimeter, and the red probe is grounded with a resistance of 8. 17 mω, as shown in Figure 3.
Through measurement, it can be judged that there is no fault in the control circuit of the injector and the engine control unit that controls the operation of the injector. Pull out the high-pressure cylinder parting line of the first cylinder, put a new spark plug on the high-voltage line of the sub-cylinder, ground the electrode next to the spark plug, start the engine, and find that the spark plug does not jump, then pull out the high-pressure cylinder parting lines of the second, third and fourth cylinders for ignition test, and none of them will jump. Unplug the plug of the ignition coil under the intake manifold, and measure the ground voltage of the No.2 terminal of the plug as 12V, and the ground resistance of the No.4 terminal of the plug as shown in Figure 4. Plug in the plug, connect the terminals 1 and 3 of the plug with a probe, and measure the waveforms of the terminals 1 and 3 of the plug with an oscilloscope when starting the engine. No square wave output was found. This means that the ECM does not control the ignition coil. Unplug the engine control unit installed under the front windshield of the co-pilot. Unplug the plug of the engine control unit, and measure the resistance between plug terminals 102 and 103 and ignition coil plug terminals 1 and 3 with a multimeter. The measured value is 0.4Ω, indicating that the line from the ignition coil control line to the engine control unit is normal.
Is there something wrong with the engine control unit? After a trial run with a new engine control unit, the fault still exists. Then unplug the plug of the engine control unit, turn the ignition switch to the "on" position, and check the power and ground wires on the plug of the engine control unit. After inspection, they are all normal. Install the engine control unit and start the engine again, but the engine still won't start. Unplug the plug of 1 cylinder injector, connect an LED lamp with resistance at both ends of the plug, start the engine, and observe the lighting of the LED lamp. Therefore, when the engine is started, the LED light does not flash, indicating that the engine cannot be started because there is no ignition or fuel injection.
The main reasons that can cause the engine not to ignite or inject fuel are: the engine anti-theft system is faulty; No speed signal; Engine control unit grounding or power failure; Engine main relay or fuse fails; Internal fault of engine control unit.
First, read the fault code of the anti-theft system control unit with the scan tool KT300, and the fault code will not be displayed. After reading the waveform of the crankshaft position sensor when the engine is started, it is found that the waveform of the crankshaft position sensor is normal. After replacing the new engine control unit, the fault still exists, indicating that the engine control module should be normal. We mainly check the grounding and power supply of the engine control unit and control circuit of this car. It is found that the ignition coil, fuel injector, carbon canister solenoid valve and oxygen sensor are all powered by relay J27 1 (relay number 109). Fig. 5 shows a simplified circuit diagram of an automobile. And the fault code shows that the ignition coil, fuel injector, carbon canister solenoid valve and oxygen sensor are faulty. So, is there a problem with relay 109?
Through analysis, if there is something wrong with the relay 10 9, when the ignition switch is in the "on" position, the fuel injector and the ignition coil power line should have no voltage of 12V, but actually have a voltage of 12V. In order to verify whether the 109 relay works normally when the engine is started, we measured whether there is still 12V voltage on the power line of the fuel injector and ignition coil when the engine is started. The result is about 2.5V, which is much lower than 12V. This means that when the engine is started, the voltage of the ignition coil power supply line and the fuel injector power supply line is too low. Pull out relay 109 in the engine compartment and connect "30" and "87" sockets with jumper terminals, as shown in Figure 6. Start the engine and it will start smoothly. Clear the fault code with a scan tool, press the accelerator pedal, let the engine run for a few minutes, and then read the fault code again, and the fault code will not be displayed.
Sandpaper the relay pinNo. 109, and then install the retested vehicle. Engine idling is still shaking. Read the data flow of the engine control unit when the engine is idling. The engine speed fluctuates between 560 ~ 840 rpm, the throttle opening is 9.5 (obviously higher than the standard value), the ignition advance angle changes between 2 ~ 10, and the signal voltage of the oxygen sensor shows that the mixed steam concentration is high. According to the data stream read, we suspect that the throttle body of this car should have been cleaned. Remove the intake pipe and clean the throttle valve with carburetor cleaner. After the throttle is basically set, the engine idle jitter is obviously reduced. Considering that the ignition advance angle fluctuates greatly when the engine is idling, we suspect that there may be something wrong with the ignition of this car. After removing the high-voltage lines and spark plugs of four cylinders, it was found that all four spark plugs were stuck with engine oil and had obvious carbon deposition, as shown in Figure 7. This means that the car is burning oil. Pull out the dipstick and find that the oil level of this car is higher than the maximum limit.
Lift the vehicle and drain the excess oil from the oil pan drain screw. The resistance of spark plug measured by ohmmeter is 1.3 mω, which is much higher than the standard value 1.04 kω. This shows that the spark plug performance of this car has declined. Four new spark plugs were replaced, and the engine idling was stable. Considering that the car would automatically turn off when it was cold, we didn't hand it in immediately after troubleshooting, but started the engine the next morning. The engine started smoothly once, and the jitter disappeared when idling. The fault is completely eliminated.
abstract
The car has the following three fault points.
1. 109 relay pin has poor contact with the socket. When the ignition switch is in the "on" position, the voltage on the power cord of the unplugged fuel injector and ignition coil is 12V. When the engine is idling, when the accelerator pedal is depressed, the pin of relay NO109 is virtually connected with the socket, resulting in the voltage drop on the fuel injector and ignition coil power cord. At the same time, the terminal of the engine control unit 12 1 has no voltage of 12V, and the engine control unit lacks power supply. Once the engine runs for a few minutes, the engine will not turn off when the accelerator is pressed, because the temperature between the pin and the socket of relay 109 will increase, and the connection between the pin and the socket will expand, so there will be no virtual connection.
2. Dirty throttle body leads to large throttle opening at idle speed, which leads to large mixed steam concentration.
3. The oil is high. When the engine is running, the engine oil rushes into the combustion chamber, which makes it difficult to ignite the spark plug.
This car failure is mainly caused by human factors and parts corrosion. If the maintenance personnel follow the requirements when maintaining the car, there will be no carbon deposit in the spark plug. The poor contact between pin and socket of relay 109 is mainly caused by corrosion at the joint of components. If we can analyze the control circuit of the car first when troubleshooting, we may not take detours when troubleshooting.
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