How to interpret VIDA stft and ltft and other things.

[Sardine]

My new to me 2005 V50 2.4i displays STFT of 1 and LTFT of 1.23. Does this mean that my STFT is 0% and LTFT 23%? If this is the correct interpretation then the car does have a serious problem. Does anybody know if my interpretation is correct?
After clearing all faults code, two codes pops up straight away: CEM-3A00, "Software Faulty signal" and ECM-531D, "DTC in Central Electronic Module (CEM) - Faulty signal."
I guess the ECM-531D DTC refers to the CEM-3A00 DTC. But what's on earth is a "Software Faulty signal"? How can software have a fault unless it is a checksum error or version error of some sort.
With the LTFT I guess I can just wait until a DTC pops up, but how about the CEM-3A00?

[RickHaleParker]

It is failing software self diagnostics ... it is a checksum error.
Did the previous owner try to tune the ECM or change the ECM? ECM may have been replaced with one containing software not intended for that car. It may have gotten some but not all the software updates in the past.

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Diagnostic trouble code (DTC) information CEM-3A00
J3300116 Condition
The central electronic module (CEM) checks the software in the engine control module (ECM).
The diagnostic trouble code (DTC) is stored if the central electronic module (CEM) registers faulty or modified software in the engine control module (ECM).
The diagnostic trouble code (DTC) can be diagnosed when the ignition is switched on.

Substitute value
None.

Possible source
Incorrect software check sum.

Fault symptoms
The engine does not start.


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284: ECM-531D Diagnostic trouble code (DTC) in the central electronic module (CEM). Faulty signal

Diagnostic trouble code (DTC) information ECM-531D

Condition
The diagnostic trouble code (DTC) is stored if the central electronic module (CEM) detects that the checksum calculated by the engine control module (ECM) does not correspond to the checksum stored in the central electronic module (CEM).
The diagnostic trouble code (DTC) is diagnosed when the ignition is on.

Substitute value
None.
Possible source
One or more diagnostic trouble codes (DTCs) are stored in the central electronic module (CEM).

Fault symptoms
None.

[Sardine]

I see. So even though the prefixes to the DTCs are CEM and ECM they are both detected and set by the CEM. In that case, I wonder why two DTCs saying the same thing are needed.

Fault symptoms
The engine does not start.

The car starts and run well? Is this a guess by the CEM only?
Now that I understand that the errors are only in the ECM, maybe the 23%? LTFT is due to a wrong fuel map stored in the ECM software. Next step is to check the fuel pressure to see if it is within spec. If it is then perhaps there is nothing wrong with the car, only that the ECM software has either been modified or is meant for another type of car. An air leak should have some bad symptoms at least.