OBDII codes from PO350 to PO362 all relate to ignition coil primary/secondary, starting with A and going through J. Just a guess, because I can't find a definitive answer online, but knowing that these codes are generic OBDII, not Toyota proprietary, I would say that the ignition coils are listed starting with A and going through as many cylinders as you have. For a V-6, I would start looking at cylinder 4 if you have a "D" error code, assuming the Toyota V-6 has direct ignition with a coil for each cylinder.