At the time of writing this article, I was still working at the Pilyugin Sosensky Instrument-Making Plant and was just determining my future and prospects. I myself know that the path of auto-diagnosis is a winding and bumpy road. Only after dozens or hundreds of repairs carried out, you begin to understand the meaning of your knowledge and realize what you need to do. Or not do.
The aforementioned car arrived with the following problem: “ABS and ESP bulbs lit up on the dashboard”.
The client is surprised: “These bulbs light up and burn. They can go out periodically, but without any logic. What’s interesting: I’m going, everything’s fine, but as soon as I go into the turn and start to slow down, all the car’s systems are cut off at the same time and the instrument panel lights up whole garland of bulbs “.
At that moment, I still had no assumptions about what was going on with the machine; there was still not enough experience. It was decided to read errors on the car, so that the first clues appeared.
I’ll tell you a little about the choice of equipment. Probably every diagnostician began his journey with his car, but I owned only a carburetor car (Volvo 340). Therefore, I took my first equipment based on which cars I had access to. It was my Kia Shuma, then still, the girl (now wife) and VW Passan B4 father. VAG-COM was definitely chosen for VAG, but with the Koreans the choice fell on Scanmatic.
Firstly, it is affordable (among licensed products)
Secondly ‚he has wide coverage for his segment.
Thirdly, excellent support for domestic cars
Fourth, frequent updates that add new cars or new functionality.
So, in 2018, Scanmatik 2 learned to work with the j2534 protocol, which allows him to cooperate with such diagnostic programs as Toyota Techstream or Nissan Consult. Also, using this protocol, you can work with various flashers, which allows you to download and write software to car control units.
Fifthly, this is a wide choice of the platform with which Scanmatic 2 can work. It can run on Android, Windows (from XP to 10), Windows mobile (not available on the latest versions).
I still use this device, since it is the only one that correctly reads my wife’s KIA Shuma (1998 onwards) machine, which Launch and Scandoc Compact cannot handle (the latter does not have an adapter for KIA-20).
I still use this scanner and it has repeatedly helped me diagnose many cars, both domestic and foreign. I highly recommend it for everyone who works with domestic cars or trucks.
We return to our Kia: we are connected by the Scanmatic 2 scanner, we select the necessary car, we go into errors.
We see errors C1513, C1283, C1260, C1611, C1623, C1616: the machine swears at the lack of communication with the ESP units, and in the end writes that the CAN bus is off.
System ESP (Electronic Stability Program) is a vehicle stabilization system. You can also often hear the name – exchange rate stability system. This system is a development of the ABS system (anti-lock braking system). If for ABS only sensors on the wheels of the car and actuators were enough, then ESP has already overgrown with a large number of sensors that give the car information not only about the speed of each wheel of the car, but also information about:
-steering wheel position
-gas pedal position
-vehicle rotation speed around its axis
Basically, the ESP system fights against skidding of the car. It constantly processes all these indicators and, in case these signals go beyond the borders, it generates control signals. The ESP system can brake any of the wheels or reduce engine power to avoid and / or exit the car from skidding.
Due to the fact that a large amount of data is constantly being processed, the ESP system needs a high-speed communication channel. This channel is a CAN bus.
Now a few words about CAN. CAN bus is a high-speed noise suppression communication channel. The CAN standard was invented by Bosch back in the 90s, but only in the 2010s it began to be actively used. CAN’s predecessor was the K-line. The k-line data was transmitted over a single wire, and strong interference interfered with the transmission of information.
Unlike the k-line, CAN uses 2 wires that carry a differential signal. One wire is called CAHH (can higth), and the second is CANL (CAN low). When turned on, a voltage of 2.5 volts is applied to both wires. With a logical “1”, 3.5 V is supplied to CANH, and 1.5 volts to CANL. With a logical 0, 2.5 volts are applied to both wires.
Differential signal gives good noise immunity.
More details (and more interesting) can be found in the article of auto-diagnostics from Belgorod A. Markin, https://autodata.ru/article/all/strasti_vokrug_koda_p500_4/
Now let’s move on to checking the CAN bus. The CANH and CANL conclusions are output to the OBD II diagnostic block, these are 6 and 14 contacts. To check, it is necessary to check the resistance between CANH and CANL, as well as to check their short to ground.
Each CAN bus participant has a terminating resistor at the input, typically 120 ohms. This resistor can ring from the CANH and CANL pins. The network resistance (if measured directly on the OBDII connector) will be around 56 ohms. Without these resistors, there will be no level matching in the network and the units will not understand each other. Also, the units will not understand each other if any of the lines (CANH or CANL) is shorted to ground or powered, since then there will be no differential signal.
In my case there was a CANH short to ground.
Now the hardest part starts: find the cause of the short circuit. On this tested car, few blocks are combined in the CAN bus (fortunately): ECU, airbags, angular velocity sensor (yaw sensor), ABS block, ESP block. In modern cars, literally everything is connected to the CAN bus: radio, each lock on the doors, headlights, turn signals, etc. At first, I thought that one of the blocks that works with the CAN bus failed, so I alternately turned off all the blocks and looked for a short circuit (short circuit). In our case, alas, it didn’t go away, so the point is wiring.
Now, when I am writing this article again, I already have experience in communicating with cars. If I were working on this car today, I would go straight to the wiring, since, based on experience, control units rarely fail (except for cars with childhood diseases, like Kalina’s ECU).
Further, the path lies in a bent form, under a torpedo. Under the steering wheel, closer to the center console, we find a 20-pin connector with a red plug. White wires come to him from one side, and black from the other. This is a CAN bus. The plug is a jumper connecting these lines. We remove the plug and begin to ring CANH on the ground. In our case, it was 17 contact.
We get into the circuit, look. 17 contact goes to the block of airbags. The airbag unit is located under the glove compartment next to the gear knob. Remove the skin and eliminate short circuit. As the skin was removed, it became increasingly clear that someone was already digging there …
Then he found out that the car was made noise insulation, in which the wires were incorrectly laid, which was the cause of the problems.
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