Technician reported inconsistencies and lack of safety warning with job cards led to an inadvertent discharge of an engine fire bottle while accomplishing a routine Engine Driven Pump Shut Off Valve check.

Narrative

Job Cards XXXX-XXXXX-XXX and XXXX-XXXXX-XXY (EA XXXX-XXXXX rev b) directs to follow sub tasks XX-XX-XX-XXX-XXX and XX-XX-XX-XXX-XXY of AMM Task XX-XX-XX-XXX-XXX. In addition; the job card does not have any reference to aircraft configuration that is required or safety warnings or notes. Starting from the first page of AMM XX-XX-XX-XXX-XXX; circuit breakers are locked out; upon event review of the situation; I have found out that the breaker for the left EDP Valve was not in the correct configuration and it prevented the valve from cycling open and closed during the check; we attempted to start over and reconfigure the aircraft to the initial point. Then; after collaborating with other Mechanics it was communicated that the check can be started directly from the start of the sub tasks and they will complete successfully. This was communicated to me and my partner that this is exactly why the job card instructs you to do the sub tasks of the AMM. AMM XX-XX-XX-XXX-XXX is scattered and easily misinterpreted. Sub Tasks XX-XX-XX-XXX-XXX and XX-XX-XX-XXX-XXY do not specifically define how to configure the aircraft and as a result I misinterpreted the procedures and correct configuration of the breakers to be open and locked out. While pushing in the overheat/ test switch; looking at the hydraulic display screen; and pulling the fire handle; While my body was twisted; I accidentally deviated from center of fire handle causing fire extinguisher to discharge.