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Weekdays beginner diagnostician – 3

Weekdays beginner diagnostician - 3 1
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Probably without exaggeration, we can call the diagnosis and repair of this car a baptism of fire …
So: Ford Kuga 2

2013 year with 1.6 ecoboost engine, automatic transmission.
The customer’s complaint is this: the car periodically twitches and stalls. It seems to be simple, but only 2 months earlier this car came to me already twice, for the first time the instrument panel was rolled back to factory calibration for heroic efforts (the car has a second owner, the first one for some reason uploaded the configuration for 2 coolant temperature sensors, although there is one fact – because of this, the tidy went wild and the temperature periodically showed 120 degrees, as a result, an error on a false overheating of the motor).
The second time the turbine bypass solenoid valve was successfully sentenced (they have diseases on these valves due to improper design).
And when the third time I saw this miracle of engineering, I did not expect anything good.
There is only one error in PCM: P0192 “Low rail pressure sensor input voltage”

Here we need to stop and remember how the fuel system itself is arranged on this vehicle: the fuel pump installed in the tank acts as a booster pump that maintains a pressure of 6.5-7 bar; essentially ‚it is a low pressure circuit, so it is maintained constantly up to the high-pressure fuel pump.
The high-pressure fuel pump assembly together with the metering valve controls the pressure from 40 to 150 MPa, depending on the operating mode, and most importantly, the rail pressure sensor works together with it in the control loop.
The analysis of the scanner variable data shows the following:

And if there are no questions from the low pressure side (parameter FLP_DSD, it is the pressure of the fuel pump in the tank.), Then from the high side there are questions.
Not only is the pressure emergency limited to 370 kPa (FRPD parameter), so also the signal voltage is 0 volts.
Yes, and periodically jumps up to 2 volts when overdriving. (not indicated on the screen.).
Everything seems to be obvious, but there are a lot of contradictions in my head:
1) if the system went into emergency mode, the signal on the sensor should be limited to 0.5 volts
2) if the circuit breaks, then there should be 4.5 volts. That is, the search option is as follows: the culprit may be both the sensor itself and the wiring, but also PCM, but so far the most expensive disappears.
I study the electrical circuit:

1) the sensor takes power directly from the power supply of the crankshaft sensor via an adhesive joint
2) Signal wire goes directly from PCM.
3) And the funniest thing is that the mass of the sensor comes to the adhesive joint of the mass of DBP, oil temperature sensor in the automatic transmission, DTOZH.
My head is spinning, and the working day ends, given that there’s also a week to go to upgrade qualifications for this brand, there’s a lot of food for thought about the malfunction …
A week later, when I had already raked up cars with typical malfunctions, and received a kick from Timofey (Inozemtsev Timofey Aleksandrovich, nickname on the forum of Legion-Avtodat “tirim”), he set about searching for a malfunction, as the car more or less moved on its own – I start the car and … everything works fine: and the error became inactive, and the pressure in the high circuit shows the standard, as if nothing had happened.
I got the idea that it’s just a matter of bad contact, or a signal wire.
And since there was no complaint about the pressure sensor connector in the rail, as well as the signal circuit wire, and the sensor signal pin treacherously dangled in the PCM connector, to begin with, I change the pin itself in the block.
Then he went on this car for a test drive…
It would seem that everything went well, everything works without a claim, I drive the car back to the service, I inform the client that the problem has been fixed, then, 4 hours later, before issuing the client’s car, I start the car and … the same symptoms as before the repair, the same error.
To say that I was disappointed with the work done is to say nothing, no less such a situation surprised the client, since I got an adequate one, and philosophically reacted to this.
For me to fix the malfunction was a matter of honor and protection of that small reputation that I earned. According to the scanner, the parameters are the same. Thoughts are different, but intuition and a sound mind interfere with the matter. As a result, I completely bury the old wiring from the sensor to the PCM, then with new pins I lay a new one. After which the malfunction is gone.
What it was: voltage sag, loss of mass or signal wire, one can only guess.
For me, this will be a good lesson, and the conclusions are as follows:
1) the work of auto-diagnostics does not endure fuss.
2) Always, in everything and everywhere reinsure yourself.
3) keep your brains in good shape and do not let yourself slack, study and digest a mountain of information that is available to you.
A month passed, the client was pleased with the behavior of the car, the malfunction no longer manifested. We work further.

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