engine light stays on! on 2003 Ford Ranger

p1633 is saying (keep alive memory power voltage low) what does this mean?

Asked by for the 2003 Ford Ranger
you may need to check your battery connections,they
could be corroded enough to cause this issue,i would also
test the battery ,if all is good there could be a possibility your having an ecm problem.
3 answers 1 comment
Perform the troubleshooting procedure associated with the P1633 code, refer to the repair manual for this information. If you don't have a manual, please check here: http://bit.ly/mitchell_repair_manuals_online
WHAT DO I DO TO FIX IT?
there is an internal battery in the pcm. it is kept alive by providing power to the pcm all the time. check your fuses for constant power to the pcm. if you have that power, then the pcm will have to be replaced because the battery is not servicable.

Roy