9-3 FWD (9440) L4-2.0L Turbo (B207R) (2009)
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The following are monitored:
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Internal control module faults
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Analog inputs
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Digital inputs
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Outputs
Internal control module faults
Upon starting, the processor (CPU) checks that the check sum is the right one for the ROM. This value is written to the RAM and then read back again to
check that the value is the same as the original one.
During operation, a check is carried out to ensure that the program executes certain routines.
See diagnostic trouble code P0601 for Trionic 8 by way of example.
1. The ROM has to be correct as the program is stored there. An error in the program could cause the control module to activate an output in the
wrong position or make entirely wrong decisions. The check sum is the sum of the program's entire code and is attached when the control module
is programmed. When the control module processor is woken, the entire program will be checked again. The check sum just calculated is
compared with the programmed one, and these must be the same,otherwise diagnostic trouble code P0605 is generated.
2. All bytes in the RAM are checked in connection with start-up. One byte equals 8 bits, and the process writes 4 different bit patterns and reads them
back. The values written and read must be the same. 4 different bit patterns are used because we want to be sure that bits do not infect one another.