The GEM is the Generic Electronic control module and it mounts to the top side of the interior fuse panel.
Central Timer Modules (CTMs)
are equipped on two-wheel drive vehicles without power windows. All other vehicles have a Generic Electronic Module (GEM)
CTM diagnostics are not compatible with the New Generation STAR (NGS)
Tester; instead, the diagnostics are internal to the module. The diagnostic mode is entered by shorting two pins of the diagnostic connector together.
The GEM inputs and outputs are designed to withstand continuous exposure to a short circuit to ground or battery voltage without being damaged.GEM Diagnostics
The GEM diagnostics are accessible with the New Generation Star Tester and the Service Bay Diagnostic System (SBDS)
. The GEM constantly monitors its subsystems for concerns. If a concern is found in one of the subsystems, the GEM will record the concern in the form of a Diagnostic Trouble Code (DTC)
There are three areas of diagnostic information useful when diagnosing the GEM.
- DTCs A record of past or present system problems.
- PIDs - The present state of an input or output.
- Active Commands Gives the ability to turn on GEM outputs without activating the inputs normally associated with the function.
Ignition Switch Positions
The position of the ignition switch is very important to proper GEM operation. Often times, erratic or unexpected operation can be traced to problems on these GEM inputs. The following is a brief description of five ignition switch positions.
When the ignition switch is in the RUN position, battery voltage should be present at the GEM/CTM RUN and RUN/ACC input terminals When the ignition switch is in the ACC position, battery voltage should be present at the GEM/CTM RUN/ACC input terminal only.
When the ignition switch is in the START position, battery voltage should be present at the GEM/CTM start/clutch depressed input. The 45 minute time is in part of the GEM module.
The GEM module does not have an OFF or LOCK Switch State input. The GEM will assume the OFF or LOCK position when there are no RUN, ACC, or START signals present.
GEM Features and Functions