Have you tried this on a vehicle yet? I'm not 100% sure what would happen here, although it seems as long no where else in the code is instructing the processor to execute this memory range or reference it,  it should just never use it. I do wonder if the processor is executing the "firmware" so to speak, and it finishes the function before it without having a command to continue/jump to a fixed memory location...and then it runs into a segment of all 0's...what will it do? I don't know enough about asm to answer that question with any confidence...Do you know where the function before it "points" to when it is done and do any other functions point to the beginning of the DTC subroutine?

Not sure how valuable it is to disable this though, as most of the diagnostics that cause problems can be disabled and the useful ones which are helpful can be retained.

Anything is possible. 

Do you want to prevent the ECU from recognizing the DTC at all, or just prevent it from storing it?

Basically find the "set DTC function", then select the memory address for the start of the function, and then open the cross references window. This way you can find everywhere that calls this function. Then you need to dig through the code and find the place that calls your "set DTC" function with the DTC number you want to prevent. Then edit that place in the code to use the NOP instruction instead of calling the function.

You would do this to disable DTCs for some systems you don't want. Such as: catalytic convertor efficiency, secondary air injection, requiring rear oxygen sensors, etc.

Yes, if you remove or disable the "store DTC" function, then you would not get any DTCs. It would be better to edit the DTC table to disable individual DTCs, or change the DTC class to one that does not set the check engine light.

Sorry for bringing up this old thread.

I'm working at the disassembling of a M2.4.1 dataset (Audi 100 S4 4.2 V8).
How ever, there are a lot of code functions etc. but nothing namend like "setDTC".

Why this is set here? Any explaination? Special "add on" from IDA?

Hrhr... Ok.

Is difficult because there aren't so many examples available for the "shitty old motronic" ;-)

RAM I don't have at the M2.4.1 which I have to "check" or?
I only have the ROM bin-file which I can analyse.
Adresse from this bin-file (line 1234h etc) are similar to "memory adresses" or?
I only have to take care about registers etc?

Is it a good idea to use a 8051-ASM to C converter?
The flowcharts in IDA looking very impressive, found some codes where it's pretty big.
But no helpful thinks I found there - I know map adresses but I don't find them in any function.
Everything "happens" in the area till 8000h for example but at A...h and B...h I have my tables but nothing point to them.
Is it possible that I have used "wrong" settings for the IDA-pro disassembling work?
8051 CPU and at analyze I left everything at the defaults (a lot of "functions")...

Hmm sure not a easy work but seems te be no other possibility to get the information

80C535??
I selected 8051 - makes this any difference? Isn't this the same? (same "family"?)
Maybe a stupid question but I only know 80x86 CPUs since some days

BoschDME I know - any "key word" to find this thread?