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Car repair situations – part 5

Car repair situations - part 5 1

Without keyword

How the control unit works

(Car repair. Situations. Part 5)

So, our counter has started counting. At the input of the register, the state “ 1 “Because the high level is valid. And this state will be valid until the moment when the transition from state 1 to state 0 (red line) is carried out. Writing to the register is performed with each clock cycle clock. The measure and the unit recorded on the cell, the next measure – the recorded unit advances to the next cell, and the new one is written in its place, the next measure – and the previous two recorded units advance further, and the next unit is recorded on the freed first cell.

By filling in the register, when the first recorded unit is on the last cell, the unit is written to the high order, and this register is reset and the next unit on the first cell is written in the next clock cycle. In the high order, the process proceeds in the same way – by filling, zeroing occurs and the unit is written to the next level.

But we still have the condition ” 1 »And the counter counts and the moment comes when the transition from 1> 0 occurs. And at the input of the register there is a change of state … and instead of 1, 0 will be written to the cells .

But as soon as the turn of the next pulse approaches, the counter stops the count, resets the data and starts to read the next pulse, the same clock cycle will read the number written to the register. The register will be reset. And the number will be read into the comparison scheme. What will we compare with? And with a number that is constantly recorded in memory.

And since we started considering the issue from the moment it was launched, it will be the number 100. Well, naturally reduced to the form of a digital signal.

I repeat: when the starter starts scrolling, the engine speed is low. And the sensor signals will have an appropriate duty cycle. Therefore, to compare the numbers you need a constant number that will correspond to low engine speeds. As soon as the ignition key is turned to “start”, the ECU receives the signal “Starter O N”. And it is precisely the number that corresponds to 100 vol. min And we get the current number from the register. As soon as the engine is started, the key is released, the computer receives a “starter OFF” signal, and a number, say 20,000, will already be sent to the comparison circuit. Why this is done I will tell below.

In addition to the “clock part” in the ADC there is also a “cycle”. We determined the rotation speed. Now you need to determine when the engine cycle begins. Otherwise, the system will not be able to consistently carry out injection, spark supply, and correction. How mechanically consistent the mechanism in the engine is, everybody imagines. It is with the timing (gas distribution mechanism) of the engine that the system takes data by means of the shaft position sensors and according to them coordinates its work with the engine. There are markers on the disks, gears. When the marker passes through the sensor, a pulse signal is formed, which differs from all others. In addition, the marker signals of the crankshaft and camshaft sensors coincide in certain positions of the engine mechanism. Based on these coincidences, the system determines: start-end-start of the next cycle.

Any change in engine speed will change not only the cycle time of the system, but also the time inside the cycle itself, when it is necessary to inject fuel and supply a spark. Therefore, there is a cyclic storage. Which captures the beginning and end of the cycle. There is also a cyclic counter, which works exactly the same as described above, but works on cyclic signals from sensors.

And in the same way a number is written on the register. Only this number will already characterize not a certain moment of time (one period from the pulse sequence), but a certain period of time (the cycle itself). But the very definition of the beginning and end of the cycle is not enough. We need to isolate and transmit information to the processor about the occurrence of the moments of fuel injection and spark supply to the cylinders according to the scheme of their work. This task is assigned to the cycle counter inside the cycle itself. It is at the command of this counter that the number obtained from the comparison and determining the moment of the same injection will be read. And only “interruption” state change from 1> 0 or vice versa will go to the processor. And at this moment, the processor will perform what is prescribed to it by the program, counting the number at this beat, it will transmit the command to the DAC.

Interruption to the processor does not occur at the moment when the event should occur (the same injection), but several clock cycles earlier. Reading cycle, cycle for possible corrections, cycle for transmitting a command to the DAC, cycle for forming a command for executive devices … something like this, if you don’t miss anything.

Now about the cards that should ” processor choose “. If we proceed from this position, then for the same revolutions, it is necessary to memorize the numbers corresponding to different revolutions. With what discreteness will we make cards: in 5 -10 – 50 revolutions? Well, if you take into account that there are indications from other sensors, on which you also need to write data to the memory … sorry, but this is not a card index, but the state archive will turn out-). Therefore, with regard to revolutions, I indicated two numbers: 100 and 20,000.

Well, you can add to them – 650 and, say 7000. Well, here, perhaps, the whole card is for revolutions. 100, I already wrote – these are low revolutions when the starter turns. This number is used when starting the engine.

20,000 – for these revolutions, the number will be recorded and the cycle time calculated, as well as the measures inside the cycle itself, it will be constantly on the comparison chart. Because to determine the injection time, say, inside the cycle you need to know how many times the current cycle number is different from the number stored in memory. That is, in fact, the initial data are recorded in the memory, which say that if the engine speed would be 20,000 rpm That cycle time would be … so much that. Accordingly, the moments of injection and supply of sparks would be produced inside the cycle at intervals … such and such. Therefore, a comparison of the current number allows you to adjust the injection and ignition times. And since it says “how many times”, it is clear what logical operation is performed when comparing numbers. And the counter “fulfills” this number and informs the processor about it. Which, in fact, plays the role of a link between ADC and DAC.

7000 is the speed at which the fuel cutoff occurs (entered by the manufacturer, may vary on different cars).

DAC works the same way ADC, just the opposite. At the input, a digital signal is generated, which is read by it for a certain clock, then the digital code is converted into a control pulse (s). When considering how it works ADC, we converted the momentum into a number … Now, try to “return” from register to input to return – get a job DAC.

I’ll show the pictures … This is not a trick, this is a visual continuation of what is written on the cards relative to other sensors. Let me explain the essence: if we turn off the clock generator for at least one clock cycle in the comparison schemes, then we will see those parameters and numbers with which the current data from the sensors are compared. Actually at this point the scanner takes data. This is because at this very moment at the inputs where the current number should be, it is not there, but the recorded one is present, photos 1 and 2

Car repair situations - part 5 2

Car repair situations - part 5 3

Well, here is the data I was talking about. The revs here, however, are a little over 16,000, but look at the other values ​​too. It is with respect to such values ​​that the current ones are compared. Actually, when the engine is running, such values ​​cannot be. They are designed specifically for calculation. And not to the processor .. but for ADC .

I will now resort to simplification and compare the processor with a switch that has many inputs and outputs. And it is located between the ADC and the DAC. The state of the outputs will depend on the state of the inputs. The state of the inputs will be determined by instantaneous values .

Instant value – this is a clock cycle clock, total one period . The time period of the clock does not change. It is constant. And the repetition frequency is high. Many opened control units and they have quartz. This suggests that quartz stabilization is used in clock generators. On quartz, the frequency value is indicated. Here with such periodicity the clock generator also works. A digital analyzer cannot show how this works in general. Too many inputs and outputs. But you can simulate by taking several digital signals and states. What we try to do.

First, let’s see two digital commands that come with a certain frequency, photo 3

Photo 3 shows the signal coming at a certain frequency. In this case, this is channel 1 of point A_B. Photo 4

Car repair situations - part 5 4

In photo 4 it can be seen that the teams also come with a certain frequency. (The same points A_B, but for the second channel). But the time it takes for these teams to pass, not simultaneously, but on channel 2 a little later than the commands on the first channel.

Time can be measured later, photo 5

Car repair situations - part 5 5

In photo 5 you can see where the end of the command on channel 1 and the beginning of the transmission of the command on channel 2.

Now take another waveform, photo 6

Car repair situations - part 5 6

On a photo 6, the oscillogram on which I will explain the principle. Red dots from 11 to 0 – I broke the bars. I apologize, but I can’t do the breakdown with the clock frequency, I can’t.

Start with eleven tact. Clock cycle – input 0 ; following 10 input clock 0 ; next … and so on to the beat 1 state is maintained 0 .

But with the advent 0 tact, we see a transition from state 0 to state 1 … ( 0> 1 ) This is it, that instant state that generates a command at the processor output, photo 7

Car repair situations - part 5 7

This moment, at the point A passed 0 tact is the next command. What conclusion can be drawn from the above? Simple: Diagnosis is underway before entering on the ADC and DAC output to the actuator. Watching passing signals, trying to understand what they contain, when they arrived or not is an empty idea.

*The forum had a topic in which a person asked a question what could be: he does not see a signal from the processor output. The driver receives a weak signal . The impulse to control the nozzles seems to be weak too …

There was an attempt to convince that it would not hurt the masses to check the nozzles. But she was not entirely successful. What is the cause of the error? It’s not quite right for a person to imagine how the processor works, otherwise it would not have been useful to look for an outlet to the nozzles from it. Can not be considered logic and logic circuits the way electrical circuits are considered: in one wire . + from the battery, through the closed contact of the ignition switch, to the relay coil and to ground … no, it won’t. At the entrance DAC code is coming. And the decoder is at the input, and the input is not one. And what the processor has at the output – here it is necessary to specifically be silent.

Well and then, the person did not even think: – “ no processor output signal “, And where did the control signal from the driver come from? Weak? And what should it be … like a signal on the secondary ignition system? In the logical part – there are already other values ​​of the supply voltage, they are much less than the voltage of the onboard network. And in the end – in the end, if the amplitude of the control pulses on the actuators (the same nozzles) is doubtful … then someone who understands will not immediately go into the control unit, and moreover, will not begin to torment the processor.

Briefly summarize the above:

· The engine control system is cyclical. It performs its inner cycle based on conditions that determined by engine .

· Coordination of the internal cycle of the system and its further changes are carried out from the moment the engine is started by the signals of the position sensors.

· The system determines the number of revolutions instantly, with the arrival of the first pulse to the ADC input.

· ICE rotation speed – the main indicator for the system.

· Any change in the operation of the internal combustion engine – entails a change in speed.

· The cyclic signals received from the sensors allow you to determine the start and end time of the engine.

· Cycle counters track these exact points. At the slightest change in speed – the cycle time is recalculated by the system. And immediately there is a change in the work of the cycle counters inside the cyclic part, which determine the moments of injection and spark supply. Recalculation of time is based on a comparison of the recorded data in memory.

· The task of comparing the current data and constantly recorded to determine how many times the current value differs from the reference. This allows the system to quickly perform data analysis and issue the necessary code at the right time to the processor.

· The processor following the embedded program executes typical for each cycle operation.

· The digital code of the processor serves to DAC team. On the basis of which it generates control impulses.

Diagnostics of malfunctions can be carried out in the system: from the internal combustion engine to the input ADC. And from the exit DAC to actuators ICE. Troubleshooting in the logical part of the control system and the software part is possible in cases where the malfunction can be detected visually (bloating of microcircuits, damage to soldering places with creeping salts, obvious damage to tracks, missing legs of circuits, after chip tuning, etc.)

With the help of measuring devices, troubleshooting can occur in the power circuits of the logical and software parts: diodes, stabilizers, etc..

The oscilloscope finds wide application in troubleshooting. In various manuals and descriptions, you can find reference signals of sensors and control signals. This is the area where you need to identify a malfunction. In other words, the diagnosis is carried out by impulse signals. But in order to understand what can lead to improper digitization, and therefore to a mismatch between the internal cycle of the system and the engine cycle, actually all of the above is written. In order to finish with the control system, there are a few points to note. After all, only essentially two sensors are considered. But what about the rest, because the signals from them also go to the control unit?

Yes, and these signals are all different. But you need to remember the following:

· Not all sensors need information during each cycle;

· Not all sensors need information even during the cycle;

· You need to distinguish between sensors that are for information and sensors that transmit a command. ( I did not make a reservation ).

· And in no way to bind the operation of sensors and actuators.

· No sensor can directly influence neither the nozzle opening nor the angle of rotation of the VVT ​​coupling .

Sensors, fixing the command to the control system:

Throttle position sensor.

They are controlled by man. The command to change the engine operating mode is given by a person. Turning on – turning off the air conditioner does the same rider, etc..

Information sensors whose data do not need to be transmitted during each cycle. ( the number of engine revolutions for which a full cycle passes I do not indicate) : Well, for example, a coolant temperature sensor. Well, why transmit the number of degrees converted to a number every engine cycle. Or let’s say the intake air temperature sensor. After all, these values ​​change slowly. What to do in such cases, because this information is needed. They do it simply: the digitized signal after the counter is written to the register during one full cycle of the internal combustion engine. And it is read as one of the clock cycles on the processor. The coolant temperature is unlikely to change over the next full cycle … and over the next … Therefore, the current number remains recorded on the preliminary comparison scheme, where the subsequent current values ​​arrive during each subsequent cycle. And for the comparison scheme, where there is a reference number and the first one recorded when the ignition was turned on, there is a ban on reading from the register, and the processor, having received the information once, focuses on it. And warm-up speed is not reduced. But the liquid temperature changed after a while, the meter recorded the current number on a preliminary comparison, where there is data recorded after on. ignition, the next step is the zeroing of the register and counter, information is recorded for comparison with the standard, then to the register …. But reading takes place at the command of a cyclic counter. And the processor receives information about temperature changes along with everything else in the next cycle. The preliminary comparison is somewhat different from comparing the number with the standard. It is executed modulo 2. And although I wrote “register”, but as a rule “they don’t fence the garden”, and instead of the register they use a recurrent (sequentially connected memory cells). There are a certain number of them. Let it be 10.

The first recorded number after ignition is on, let it be 000000000111, and corresponds to some coolant temperature.

Only recurs will be recorded 1 . Therefore, with the ignition on, we will be in the first three memory cells 1. And the rest are empty. After some time, the number will be: 00000000 1 111 (the fluid is heating up, the signal amplitude increases). Next is a comparison without transferring to the high order: and 1 (red) will fill the first cell, and the rest will advance one cell through the recruitment (will be overwritten.) As soon as the recursion is filled 1 ., the next measure, the new current number will be submitted for comparison with the standard (the ban on reading will be removed from the register). The result of how many times it differs from the standard will be read by the processor.

But this same current number will be written to the preliminary comparison scheme, and all subsequent current temperature values ​​will be compared with it. This is clearly visible when the engine warms up, when it starts to lower the engine speed to XX. If the temperature does not change, then the processor will be guided by the data obtained earlier. This is how the logical part cuts off “especially annoying sensors”.

Sensors, information from which is analyzed per cycle. These are sensors such as MAF, MAP O2, knock sensor.

Let’s see the oxygen sensor. The cycle counter cuts off a certain period of time (a full cycle of the internal combustion engine) and when digitizing, we get the number from the oxygen sensor. This information is transmitted to the processor..

But the fuel correction will be performed only in the next cycle. Therefore, corrections in the control system are called timesSmi They are implemented in time. Cycle – receiving information; The next cycle is corrections. That’s why, when we look at the oscillogram of a recreation center and see that the time for changing its amplitude from minimum to maximum in the period is increased (the sensor is “frozen”) – such a sensor goes to discharge. Because the wrong number will be recorded during digitization (now I mentioned an additional characteristic: the rise time of the amplitude), which I mentioned earlier. Here you have the theory in practice J .

Executive devices. These are “immediate subordinates” DAC. These are ignition coils, nozzles, stepper motors, controlled dampers, various valves, etc. And they work on impulse commands. And they’re on the drum, what kind of sensor readings are there, what corrections … they execute commands DAC stupidly as riot police.

This seems to me, the main reason why many get confused and rush about when troubleshooting. And the confusion comes from the fact that many do not know “who is in charge” in the management system. And in control systems, the “control object” has always been and will be the main one. In our case ICE. Here it is all done for him. This is all done for him. And he determines the working conditions of the computer.

A simple example: Remotely opening gates in your garage, they did not respond to the key fob signal. What will you watch? Check the key fob for the LED to light up. Okay. Next, open the receiver unit and begin to check if there is a signal at the input, whether the executive relays are triggered, whether power is supplied to the winch motor …

Try to register a second remote control in the remote control (adaptation of the shutter to perform J) … The path is not bad. But long, because it is not entirely true. Climbing into the control system without being convinced of the correct operation of the mechanics of the control object (gate) is probably still premature. It would be more correct to try to open the gate manually, and make sure that the mechanism works properly. And as usual, “suddenly” it is discovered that the chain has flown and the winch is jammed.

It is very difficult on the forum to explain why you do not need to climb into the control unit and torment it, if not + on the nozzles. Therefore, without imposing anything in the first person, I’ll just try to tell you what I pay attention to when conducting inspections when troubleshooting

MARKIN Alexander Vasilievich

Tavrovo microdistrict 2, lane Parkovy 29B
(4722) 300-709


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