Porsche PADM sensor description

1、Cause of damage of original engine mount

The engine mount consists of three parts, the housing, the internal magnetic fluid, and the sensor. As long as the shell does not leak, then obviously it is good, and in my more than 100 cases of repair experience, I have only encountered one case of a leak, and the leak itself did not result in a fault code being generated. The inside is filled with magnetic fluid, and there is a set of coils to the magnetic fluid power, the coil is easy to check, there are a total of 5 wires in the plug, of which 2 thick is the coil through the wire, as long as you measure the resistance value of this coil is about 1 ohms, then it is normal, and I have never encountered coil damage. All the engine support damage I encountered was caused by sensor damage without exception. From its fault code, you can also see that it pointed to the sensor. The fault code is the grounding short circuit of the sensor signal line, and the code is 001013 or 001023.

So why is the failure rate of the original sensor so high? All the damaged sensors I took apart had the same characteristic, the measuring chip had come off, maybe because of the way it was fixed, the original was glued, and the engine mount was in an operating environment that vibrated at any time, maybe because some intense driving action caused a sudden increase in the pressure of the magnetic fluid and washed away the measuring chip. Here are some pictures of the inside of a damaged sensor:

Knowing the cause of its damage, it is not so difficult to repair it, only need to copy a sensor with the same parameters, and it is best to improve it, and the final installation is relatively simple.

It's not a very complicated sensor, and most sensors are like this, a Wheatstone bridge chip measures the change, then amplifies the signal through the amplifier chip, and finally adds some filtering and protection circuits and outputs the signal, and that's it.

2、About the new sensor

We live in JiangSu, China, an industrial city. and it has a complete range of automobile industries. It is not difficult to make such a simple circuit board, but the more complicated thing is its calibration. Fortunately, I am a Porsche repairman, there are many samples for me to test, So the job of calibrating it can be done. But I still want to talk about its calibration, if you use OBD to read the data of the original sensor, you will find that at a normal atmospheric pressure, in the parking or idle state, most of the original sensor reading is between -100kpa and 0kpa, and each car is different, even the left and right sides of the same car are different, I don't know what Porsche's thinking is, but I think it's logical that the exact reading at this point should be 0kpa or slightly above 0kpa, because the MHD pressure on the car is either a normal atmospheric pressure, which is 0kpa, Either the engine bracket is affected by gravity and its actual pressure should be slightly higher than 0kpa, At rest, it can never be negative pressure. But fortunately, the error within 100kpa does not affect the actual work of the magnetic fluid, Because its total range is more than a dozen times that of 100kpa, and its working logic actually depends on the frequency of signal change rather than on the actual value size. so I did not dwell on this, perhaps Porsche has its own unique considerations, but I think this is more likely to be the production error of the original sensor, this thing is not very high technical content. But I do know that if you calibrate the initial voltage of the sensor higher, then the engine computer will recognize a higher initial value of pressure, then the MHD energized intervention time earlier. However, this can not be felt by the human body in actual driving, because the working current of the magnetic fluid in the idle state is extremely weak, close to 0, only when the SC mode is opened, the intense driving, it will become the most sensitive, and in any corner, the current will suddenly increase to more than 3 amps, which is when it really works. I ended up not correcting the error of the original sensor, although it was not difficult, I ended up taking an average of the original error to calibrate the new sensor, so in theory after you load the car, the OBD should read the value between -50kpa and 0, which I want to make clear here, it is not my sensor error, and I did it deliberately. I think copying the original data is a safer strategy.

Of course, in order to avoid the same high failure rate as the original factory, I made some changes to the chip, the principle is the same, Wheatstone bridge measurement, amplification chip amplification, after some filtering finally output signal. However, I installed the measurement chip in a different direction, and changed the package form, so that it was wrapped up, and then welded to the circuit board through the pin, so that it would be difficult to fall off or be washed away. The following are some pictures to illustrate this change.

3、Housing and mounting method of the sensor

In order to facilitate installation and transportation, so I made a shell for the chip, of course, the cost of plastic shell is lower, but considering the sensor itself is not expensive, so increase the cost of making an aluminum shell does not matter, although the processing is not very delicate but it is at least very useful, the following is its internal structure diagram.

Because the original plug integrates the coil wire and sensor wire into one, and the plug cannot be disassembled (991 and 981 are like this, but 982 can be disassembled, so I provide another shape product for 982, and its installation will be simpler, but their principle is the same), so I keep the two coil wires in the original plug. However, I took the other three sensor wires in another direction, which helps to reduce the number of sensor parts and reduce unnecessary costs, and also provides a new sensor plug for easy installation. The following is the specific picture description.

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