Debugging update/transfer rules If you suspect that there is a problem in update rules or transfer rules (example: Expected transformations are not taken place). In which case go to the data load monitor in BIW and select the data package you like to debug as shown below. Right click and select “Simulate update” . 
Following dialog will appear:
Choose update rules/transfer rules for debugging. You can also choose the specific records you like to debug. Once you are ready, select “Perform Simulation” and enjoy the debugging of the transfer/update rules. Debugging “Start routine” Above process cannot be used to debug start routines, which get executed before the update rules are called for each data packet. And this start routine is called in the background process. Even statements like “BREAK-POINT” are ineffective in breaking the execution process. You can use the following trick in this case: Have an infinite loop in the start routine: ** for debugging purpose WHILE sy-subrc EQ 0. ENDWHILE. 
Trigger the data load process and the process will go into inifinite loop. You can see the process in transaction SM50 (process overview). Select the process and debug. Once you reach the while statement, change the sy-subrc to 1 and proceed with the debugging of start routine. CAUTION: Don’t forget to delete the infinite loop once you are done with the debugging.
Following dialog will appear:Choose update rules/transfer rules for debugging. You can also choose the specific records you like to debug. Once you are ready, select “Perform Simulation” and enjoy the debugging of the transfer/update rules. Debugging “Start routine” Above process cannot be used to debug start routines, which get executed before the update rules are called for each data packet. And this start routine is called in the background process. Even statements like “BREAK-POINT” are ineffective in breaking the execution process. You can use the following trick in this case: Have an infinite loop in the start routine: ** for debugging purpose WHILE sy-subrc EQ 0. ENDWHILE. Trigger the data load process and the process will go into inifinite loop. You can see the process in transaction SM50 (process overview). Select the process and debug. Once you reach the while statement, change the sy-subrc to 1 and proceed with the debugging of start routine. CAUTION: Don’t forget to delete the infinite loop once you are done with the debugging.
However, I am confused by your statement “Above process cannot be used to debug start routines”. I’ve always reached a break-point before the start routine is executed. Up to version 3.5 at least.
I believe you have explained How to debug from InfoSource to Infoprovider(2lis_aa_vaitm to 0sd_co2). How do i debug from ods to ods/infocube Update rule. there is no option of PSA. can you plese let me know how we can achive that!!
regards,
Shiva
Debugging should be possible with the simulate in this case also. If not you can use the second technique of having an infinite loop.
Best regards,
pavan
There is an option to update from ODS to Cube via PSA. You can simply create your own InfoPackages under InfoSource 8Dirk
Just wanted to say that I regularily have used the debugging functionality in the Monitor to debug the start routine (for Update Rules). Just search for 9998
Thanks,