The electronic control module (ECM) — also called the powertrain control module (PCM) or electronic control unit (ECU) — is a computer which controls the electronics in an automobile. The ECM 1 is one such computer; it has a fuse is installed to protect the computer from sudden power surges or other component damage — the fuse will blow before any damage can reach the ECM. Many component defects can cause your ECM 1 fuse to blow.
Although complaints have been reported about the O2 sensor causing the ECM 1 fuse to blow, in reality it is not the O2 sensor causing the problem — it is the placement of the O2 sensor. If the wires leading to the O2 sensor rub against the exhaust, it creates a ground; once the O2 sensor is grounded, the fuse to the ECM 1 blows. The O2 sensor must be installed in a different place to ensure the wires do not short-circuit.