This entry – is about a very widespread diagnostics “method”. I suppose many diagnostics specialists will recognize their style. Unfortunately, it will not be easy to find someone who doesn’t t work like this because this is a prevalent method. Unfortunately, famous even in dealer centers. My suggestion to the customers is to change the diagnostics specialist if you notice that your diagnostics specialist “performs” in such a manner.
What is the characteristic of this work method? When the diagnostics specialist receives a car, he deletes the error messages first-hand. And “works” with the error messages, which immediately re-appears. FAIL – that is the softest I can say.
Why do diagnostics specialists act like that? The answer is simple – it is “easier” for them. For low-level diagnostics specialists, these “past” error messages complicate identifying the main problem. Or main issues, if there are several of them. Yes, the error messages can be interconnected, and then it should be understood the cause and – consequences of the general problem. A second reason is the “professional” environment of low-qualified diagnostics specialists; there is an opinion that the error messages can appear “without” any reason. Or, for example, because the battery was low. Yes, such cases can be, but a qualified specialist will analyze each error message and make sure about why they appeared. And finally – if the diagnostics specialist has “diagnosed” the same car previously, deleting the error messages, he can show a “clean” DME error message memory and confirm his ability to repair the vehicle. Even if the previous error messages are recorded repeatedly, or, put simply – cheat the customer with no claims.
Why is it entirely wrong and can’t do it? I will dismiss that it is not OK to cheat the customers and hide their incompetence and/or unsolved problems is not worthy of the master. I will move to technical aspects:
a. after such deleting of the error messages, immediately only the most “simple” error messages “appear”, for example, stable defects of the peripheral connections and/or actual damages of their sensors/actuators. For example, electric connection issues of some sensor or complete loss of the sensor signal;
b. after such an error message deleting, the previously mentioned “simple” error messages, which are sporadic (appear and disappear), will not appear. Unfortunately, precisely the sporadic error messages dominate in all range of problems. The reasons are straightforward – the working conditions of all vehicle systems are harsh. Swift changes of the temperature in a wide range; vibration; humanity; water, changing supply voltage – these are only some of the aspects;
c. most significant part of the error messages characterizes functionality problems. These problems are identified in exact driving conditions, or even more complicated – in current driving conditions when DME performs specific functionality tests. Several examples. Injector flowrate measurements in medium load range; performance tests of the CO catalytic converters, measuring their ability to burn the fuel, performing 20 sequential tests during exact driving conditions. There are hundreds of such tests for modern DME – even thousands;
d. finally – when deleting the error messages, the diagnostic specialist deletes not only them but also a range of invisible (unavailable) registers for internal use, which fundamentally changes the DME performance mode. More about it read here.
Deleting as if “old” error message, 99% of fundamentally important information regarding performance problems of DME (and any other module) is lost. Doing so, a successful repair is simply impossible. You will visit such a “diagnostics specialist” repeatedly, every time, something will be tried, but there will be no result. Even more – “repairing” the car in such a manner, you will have serious troubles! I will mention only one example.
Here freeze-frame of the INPA error message:
As we see, the error message regarding oil pressure is recorded in the DME error message memory. The problem is recorded two times (so it is not a one-time problem during a long period). The oil pressure, measured by DME, was twice below what was required. And that is only logical – this error message is recorded only if the estimated oil pressure is at least (almost) two times lower for at least 5 seconds in line. We also see that both times this problem was for a cold engine; on the go – 1600/2600 RPM driving conditions.
If the first “job” of the diagnostics specialist is deleting the error messages, these error messages will disappear from the DME error message memory. This error message memory will not repeatedly appear even if the diagnostics specialist will “run” the car in idle because at least 5+ seconds long unchanged conditions (RPM, required torque) of work are needed. And what about other parameters – engine coolant/oil temperature, etc.? Of course, these parameters will not correspond to the ones by which this error message was previously recorded. Summary: whatever the diagnostics specialist would do after receiving the car and deleting the error messages, this error message will not be recorded repeatedly. At the same time – the oiling problem of the engine (and the problem is severe) hasn’t gone anywhere!
This is only one (of many) examples of how the diagnostics specialist uses deleting such error messages as a first step but causes only considerable trouble! If such an oiling problem is not solved immediately, each ride can be the last for this engine. And then the expenses will be several thousand EUR.
How to proceed correctly?
1. DO NOT delete the error messages! By default, it has to be assumed that each error message is recorded for a serious reason!
2. check each error message and its freeze-frame. Analyze data regarding error message and conditions during which it was recorded;
3. analyze live data connected with each error message;
4. create a screenshot of the freeze-frame of each error message, and save it on the computer. This information is very often beneficial in further diagnostics; storing appropriate live data menu;
5. delete error messages only AFTER repair works;
6. perform re-adaptation of the engine after repair and deleting of the error messages;
7. if possible, check live data in current problematic conditions to ensure that the problem is gone.
In short, the oil pressure (in the image above) problem. From several “diagnostics specialists” I have heard – well, we replaced the oil pump (or the valve/sensor), and the error message disappeared. This is NOT an indication! With a significant probability, the customer did not manage to repeat the conditions (immediately/during a short period). In this case (oil pressure, static), the PWM data of the pressure regulation valve! These data will indicate how much “effort” the oil pump will need to maintain the required pressure. If PWM drops below the mark of 30 .. 35% and/or DME for even a short moment does not manage to maintain the required oil pressure – this hub has problems. And the recording of the error message is just a matter of time. Sentence of this paragraph – confirmation of a positive repair job is not the nonexistence of the error message but correct live data in specific engine work conditions.