This car came with a problem: “The speedometer is not working.” To the question “how exactly doesn’t it work?”, The client replied that “sometimes it works and the speedometer needle rises, and sometimes the arrow does not rise at all or rises and falls, or stands in one place and shakes.” In a word, “leapfrog”, one must look for a reason.
I am sometimes asked on the “troubleshooting algorithm”. Kindly:
– I lift the car to the lift
– I turn on the gear, the wheels spun
– I look at the speedometer – “silent”
After that, I connect my device to check these sensors:
You can read about this device and others like it on the Legion-Avtodat portal: “Devices for auto-diagnostics – 1”, “Devices for auto-diagnostics – 2”
I emulate speed and see that the speedometer is working and shows the speed:
Conclusion: the speedometer is working, wiring to the speedometer, connectors, etc. – are working.
What you need to know when conducting such checks: “What is a speed sensor and how it works.” A lot has been written about this on the Internet, I’ll say in short: “The speed sensor is installed on the gearbox and informs the on-board computer about the speed of the car when the car is moving.” There is a car movement – there is a signal. No movement – no signal. In our case, “there is movement – there is no signal or it is distorted.” It remains to answer the question: “Why is this happening?”.
As the saying goes, “seven spans in the forehead is good, but you need to have a book on hand” – no matter how smart you are, and you need to look at the diagram of what and where it goes At my fingertips during this repair was a diagram:
The logic of science is accurate: we checked and made sure that the signal from the speed sensor is coming (from the speed sensor connector), the speedometer is working, plus or minus are present – all this is excluded from the test and now it remains to determine the operability of the speed sensor itself. We get to it, although it’s not very convenient:
An external inspection shows that the cause of the malfunction is in the sensor itself, or, more precisely, in the “gear wear”. Everything is almost exactly the same as in the article two years earlier – “Hyundai Santa Fe I. The speedometer does not work”
The client was asked to buy and replace a worn plastic gear, but he did not agree, said that “it is better to put everything new.” No problem. After replacing the speed sensor, the “fault is gone”.
And finally: this fault is a “typical fault”. That is, a kind of “template” that can be used when diagnosing a car. But I would like to advise (and not only on this example) – do not use templates primitively, but just keep them in mind: a “one-on-one” malfunction is extremely rare and, if you try to repair cars only on the basis of certain “templates from articles”, then you lose customers quickly. The main thing in troubleshooting is the determination of the section of the electrical circuit where the signal disappears. And then everything is simple. Successful repairs, colleagues!
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