Malfunction of mechanics or electronics?
When carrying out diagnostic measures on a car, sometimes it becomes necessary to determine as accurately as possible: “Does the malfunction relate to mechanical failure or problems in the electronics or the electrics?”. It is important. I will share my experience in solving this issue.
So, the car Mitsubishi Space Star 2003 release. An indicator on the dashboard blinked, indicating that a malfunction occurred in the gearbox. DTC 41: “1st gear ratio is not standard.” More precisely: “Code No. 41 1st gear incorrect ratio. If the output from the output shaft speed sensor multiplied by the 1st gear ratio is not the same as the output from the input shaft speed sensor after shifting to 1st gear has been completed, diagnostic trouble code No. 41 is output. If diagnostic trouble code No. 41 is output four times, the transaxle is locked into 3rd gear as a fail-safe measure, and the N range light flashes at a frequency of 1 Hz. “
To troubleshoot, you can use the manual tooltip:
But you can go the other way (bearing in mind the tips from the manuals).
To find such a malfunction, we need:
1. Scanner and / or oscilloscope
3. Repair manuals for this vehicle
I want to make a reservation right away: I have never been special in the diagnosis and repair of gearboxes. However, everything is included in the concept of “car diagnostics”, including troubleshooting of gearboxes: greatly simplifying, we can say that when conducting diagnostics, we are looking for the answer to the question: “What is missing, what has changed or was lost in the transmission of the signal from the terminal sensor to or between the on-board computer. ” And this, by the way, will help answer the question: “What kind of malfunction in the gearbox is electronic or mechanical?”.
Agree, it is not only useful to know this, but it’s also important – that the client can correctly distribute his forces and means and have a clear idea: whether he will spend money on mechanical repairs or not. Because fault code 41 is a diverse code, I will give some reasons for the occurrence of this code:
1. Malfunction of the pulse generator (speed sensors)
2. Failure of the clutch drum
4. Wear of internal gears of automatic transmission (models with 4-speed automatic transmission)
5. Faulty planetary gear
6. Faulty brake first gear and reverse gear
7. Failure clutch gear
8. Brake failure of an additional planetary gear set (models with 5-speed automatic transmission).
The repair manuals correctly state that “automatic transmission failures can be caused by malfunction of engine systems, improper adjustment or internal malfunction of electronic or hydraulic gearbox control systems, mechanical gearbox malfunction. Therefore, ALWAYS start the diagnosis by checking the level and condition of the oil in the automatic transmission“.
How else? Therefore, the first thing – I checked, made sure that everything is fine. Next: car on a lift. I take the scanner, delete the error, start the engine, shift gears, control the parameters:
– engine speed
– input shaft rotation speed
– output shaft rotation speed
– vehicle speed.
At first, while the automatic transmission was not particularly hot, these parameters corresponded to the speed conditions of the engine and gearbox, the malfunction did not manifest itself. But after some time, the scanner showed that the wrong signal is coming from the speed sensor of the input shaft of the gearbox. The scanner again fixed an error. Here it is time to turn to the oscilloscope. We connect the oscilloscope and watch the signals from both gearbox speed sensors – input and output shafts.
By the way: Mitsubishi cars can bring surprises (example in the article “Mitsubishi Montero Sport. Box emergency mode” ).
The engine idles, the automatic transmission is in the “D” position, I look at the monitor – what’s wrong with the signals?
The waveform shows the missing pulses from the sensor of the primary (input) shaft:
1 IN is the input shaft, 2-out is the output shaft
The primary shaft receives torque from the motor, and the torque is transmitted to the wheels through the secondary shaft. If we take into account that at the moment, the engine is operating at a constant speed, then the pulses must go at a constant speed. Ideally, on the oscilloscope screen, we should not see any gaps. With mechanical failures, the signals would be incorrect on both the input and output shafts.. For greater clarity, you can connect the third channel of the oscilloscope to the output of the tachometer. Then we could observe with such a defect that the speed of the primary (input) shaft does not correspond to the engine speed.
The conclusion is this: a malfunction of the input shaft speed sensor. His replacement helped resolve the issue. Malfunction resolved.
I can note that such semiconductor speed sensors begin to produce incorrect, so to speak, “malfunctioning” signals during heating (sometimes during cooling). Either some physical properties of the semiconductor are violated, or something else, but from experience I will say: if a sensor of this type begins to junk – start troubleshooting from it. Perhaps this will save a lot of time. And one more thing: one of the verification options may be to lower the temperature of the speed sensor being checked if it is heated: cool it with a fan or something else and check again. The method is not one hundred percent, but it helps.
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