When you buy a car and the seller says: – Is the light on the panel on? Come on, there’s nonsense! Delov for five minutes in any car service. And I’ll give you a discount for this. Well, hands on?
… and when they say this to you – better not believe it, it’s a blatant deception, because after buying a car you have to spend money, time, nerves. And even that is not a fact that it will be possible to eliminate the “nonsense” in a car service. Some auto centers cannot solve such issues.
A car got into our car service with a malfunction: “open circuit of the front right sensor of the ABS system”.
“There are MRE speed sensors on this car, they cannot be checked with an ordinary tester,” he probably said out loud, because the client confirmed: “I was in another service recently, they rummaged and said that they can only check by replacing a similar sensor but they don’t have a substitute.
– And then what? ”I asked
– Offered to buy a new.
– Just take it and buy it? And if the reason is not in the sensor?
– Well … then all responsibility rests with me, they said.
– Cool! – I summed up.
Really cool. Already how many pages are written on the Internet for these sensors, and things are still there, live in the century of old speed sensors. But is the devil really terrible?
Here is this sensor that works on the principle of magnetoresistive effect.
The word is scary, but in fact everything is simple.
Such speed sensors (Active Wheel Speed Sensor) belong to the so-called “active sensors” and for their work requires 5 or 12 volts. Let’s start by comparing the operating principles of an active speed sensor and the so-called “passive”, that is, familiar to all of us induction. Everything is clear in the pictures, I think, no need to explain.
So, the principle of operation of the passive speed sensor:
On the left is the waveform that can be seen during its normal operation. Right: “A” – the required air gap and the so-called “speed controller” or “comb” (open).
Next, we look at the principle of operation active speed sensor:
1. Multipole ring – multi-pole ring (photo will be below)
2. Sensor – consists of magneto-resistive elements
3. Sensor housing
Multipole ring – represents a magnetic layer deposited industrially, moreover, it consists of alternating N and S poles arranged in a circle and integrated into a bearing, for example, into an inner ring, as in the photo below.
This is a photo from previous repairs and it can be seen here that this magnetic layer collapsed, which was the cause of the ABS system malfunction in the car. By the way, if you look closely, on the remaining layer you can see clear segments, which are exactly the poles of N and S.
When the wheel (and, of course, the bearing) rotates, the N and S poles alternately pass the sensor (magneto-resistive element), which gives a digital signal to the control unit. It should be noted that Active Wheel Speed Sensor , unlike an inductive type speed sensor, it can record speed starting from zero.
It must be assumed that such sensors will be used everywhere (until they invent something new), and they have these advantages compared to inductive speed sensors:
1. Determination of speed starting practically from zero value
2. Determining the speed of movement both forward and backward
3. The design is lighter and more reliable.
4. Low sensitivity to electromagnetic interference
5. Low sensitivity to changes in the air gap between the sensor and the magnetic ring
6. Good tolerance to temperature fluctuations, vibration
To fix, I propose to see a few screenshots and photos:
The difference between passive and active speed sensors
Passive and active speed sensor signals
Location Multiple ring (multipolar ring), options:
We assume that the principle of operation of active speed sensors figured out. Well, we go further: we need to understand the specific cause of the malfunction? The trouble code that the scanner provides is just a code, a description that looks like a cloud of assumptions:
– the speed sensor itself is faulty
– faulty electrical wiring (open, short, etc.)
– problems in contact groups (connectors)
To check the speed sensor, I used a device that I invented and assembled on my own and which I already spoke about, watch the video:
It turned out that the speed sensor is in good condition, and the problem most likely lies with the electrician – somewhere there is a bad contact, a break or the like.
After inspection, the malfunction was detected:
Please note that on the right side of the photo, where the harness goes into the engine compartment, the metal has a roughness. That is, it was once ruled to give a decent look (and sell, naturally!). Conclusion: “Once the car was in an accident, there was a blow to the right”.
In the photo: everything has been restored by electrics. And as it was, I can only say in literary words: “I would have to tear my hands off for such a job!” How exactly was it? The wires are twisted in a hurry, somehow, the electrical tape is wound with “gaps” – just to hold. “And why not?”, – probably those who twisted the electrical tape thought (of course … they would only have to throw off the car and sell it, but the grass doesn’t grow there … “)
Well, I did it reliably and almost for centuries: on adhesive heat shrinkage, carefully, carefully. Why redo the work twice?
Bye. All successful repairs and repairmen!
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