I've used a US issued card with a four digit PIN at an ATM in KL with no problem. I was downtown in the mall connected to the Ritz-Carlton; put my card in, my 4 digit pin, and out came the Malayasian Ringit's.
No problems, but just keep in mind this was only one machine in KL in a tourist area. Also - If you plan to bring any local currency in, I believe you must declare any Ringit's over 1250, IIRC, when entering or leaving the country. Use an ATM or convert money after Customs & Immigrations.
SDF_Traveler