Frozen Values
For every diagnostic trouble code, pre-defined parameters are frozen and stored in the control module. The frozen values are stored immediately after the malfunction has been detected and gives a "picture" of the conditions when the malfunction was stored.
Status identifier, Counter and Frozen values are the most important factors to deciding the malfunction's nature, that is, to decide:
- when the malfunction was detected (frozen values, counters)
- what the driving conditions were at the time (frozen values)
- status for the test (self-diagnosis) (status identifier)
- how frequent the malfunction is (counter).
In newer car models, frozen values consist of a number of global (common) general parameters as well as a number of control model-unique parameters. Global may be:
- Road distance
- Battery voltage
- Passenger compartment temperature
- Outside temperature
- Engine running
In addition to these, the diagnostic trouble code-unique parameters are stored which are especially selected parameters for the diagnostic trouble code.
Most parameters in the frozen values are the same for all malfunctions and indicate a general condition when a malfunction was detected, for example:
- Road distance
- Outside temperature
- Engine speed
- Load
- Coolant temperature
- Vehicle speed
- Battery voltage
- etc.
Some of them have been selected to give a better understanding of the specific malfunction.
When erasing diagnostic trouble codes, stored frozen values are also erased.
HINT: Reading out and interpreting these frozen values make it easier to understand when in time the malfunction occurred, as well as under what driving and environment conditions the malfunction was detected, related to when and how the customer experienced the symptom.
A malfunction that is detected is assessed by the control module's self-diagnosis. First after, e. g., a certain time, a certain number of driving cycles, certain driving/operation or other conditions, the control module decides if it is a real malfunction or not.
When self-diagnosis has determined that a real malfunction exists, you can say that the malfunction is confirmed and the malfunction is stored in the control module's trouble code memory in the form of diagnostic trouble codes.
If a malfunction disappears, the diagnostic trouble code will remain for a tome in the diagnostic trouble code memory, but the status of the diagnostic trouble code changes. How long the diagnostic trouble code is stored in the diagnostic trouble code memory is different from control module to control module, as well as between different vehicle models (generation of vehicle model).
In some systems the diagnostic trouble code will be stored until it is erased with the diagnostics tool. In other systems the diagnostic trouble code is erased automatically by the control module after, e. g., a certain number of malfunction-free driving cycles. A new driving cycle (operation cycle) is usually started every time the ignition is turned on.
Information about the nature of the malfunction is stored for every diagnostic trouble code:
- when the malfunction was detected (frozen values, counters)
- what the driving conditions were at the time (frozen values)
- status for the test (diagnosis) (status identifier)
- how frequent the malfunction is (counter).
Exactly what is stored is different from control module to control module, as well as between different vehicle models (generation of vehicle model).
If the system is provided with warning light, it is lit when the ignition key is turned to position II. The warning light will go off after a certain number of seconds when no malfunction is detected on the control system.
The warning light will be on in case of a malfunction of the control system. The warning light will be lit first after the malfunction is confirmed as a real malfunction.