Typical behavior of "repairers = changers" proudly called ''diagnosticians''- is to connect the diagnostic device to the car, erase all error codes, and then handing the car to the customer with information that the errors of course - were but have already been removed and if they will not return so the problem is solved. What a magic repair!

Some are more generous and give their clients a list with errors that were saved in the drivers' memory. Such activities do not have much in common with professional diagnostics and in fact to find a real fault is more difficult.
Every day we meet situations in which the customer asks a question: I have saved error codes 0746 0776 0796 0766 0705

of course at the end the customer
ask the question: what it can be and how much the repair will cost?

A well-made diagnosis is the key to achieving success but in order to be able to draw meaningful conclusions, we need a lot more information.
Based on the above-mentioned errors, it is save to say that the gearbox controller (or whole mechatronics) could be thrown into the trash but for sure?

This list of error codes looks scare but take a look closer of our table.
The first column is the description of the error, the second is the DTC number, the third is the information if the light on the instrument cluster is on, the fourth if the error is stored in the memory, and the fifth if the error is still active.

What conclusions can you draw with only such a list? What if I add information that the TCU was connected outside of the car during make a diagnosis protocol?

Then we automatically look at communication errors and see that they were apperad during this diagnosis (office temperature 21 degrees, 2 seconds from "controller reset", some parameters have substitute values such as vehicle mileage 131070, of course also it could be a real mileage, but we know that we have plugged in the TCU on the table and we have specifically prevented these errors from appearing.We know that these errors are insignificant from the point of view of the client's problem).

Further on the list we have errors:

• Wählbereichsensor : Ungültiger PRND Wert (Bitkombination)
• Ventilfehler : KÜB Ventil unterbrochen
• Ventilfehler : DNR Ventil unterbrochen
• Ventilfehler : Sekundärventil unterbrochen
• Ventilfehler : Primärventil unterbrochen

What give us:

• Position range sensor: Incorrect PRND value (bit combination)
• Valve error: KÜB Valve - break
• e.t.c.

With only the error codes and  inexperience, we can confidently say that the position sensor and 4 solenoid valves are defective (or damaged control solenoid valves), "environmental parameters" support the argument: "mileage at the time of error 71364km, 12.5V supply voltage" . We can see further that the temperature of the oil is 26 degrees, the speed is 0, there is no working pressure, the problem only occurred once, with the run, in which there was also the problem of rotation sensor - conclusion? The car is standing on the lift, and someone connected our TCU without a hydraulic unit (these 5 errors always exist together, if someone connects the electronic controller itself and turns on the "ignition").

So we have two "significant" errors: 0793 and 0722

• Drehzahlsignal nSecd kein Signal (oder Sensorversorgung ausgefallen)
  
• Drehzahlsignal nOut kein Signal (oder Sensorversorgung ausgefallen) 

What give us:

• Speed sensor: nSecd - no signal (or no rotation sensor supply)
• Speed sensor: nOut - no signal (or no rotation sensor supply)

What are the "environmental" parameters we see?

Error 0793 occurred 8 times, the first time at 71358km at supply voltage 13.9V, during gearbox temp (39 degrees) and working pressure 12.3 bar (engine had to work), the last error occurred at 71364km, voltage 13.9V and pressure 63.60bar when the gearbox was already hot (70 degrees).
Error 0722 occurred 4 times ... the rest of parameters similar to the previous error.

We see that over a distance of 6 km the problem occurred several times. We also know that the electronic unit had a damaged power supply for the speed sensors, which also confirmed errors stored in the unit's memory. The cost of the repair is marginal compared to the cost of purchaseand replacement of the entire mechatronic assembly, which should be replaced, making decisions based only on the list of errors.