Contents

GEM (General Electronic Module): its place in the electronic management system

Role of the GEM

Maintenance of the GEM

 Our modern vehicles are full of mysterious boxes scattered throughout their structure. The GEM, an electronic management module located in the passenger compartment, is one of them. Let’s take a look at it.

 GEM: its place in the electronic management system

 A general electronic module always has the same architecture and is composed of the following:

• Electrical power supplies (battery voltage, masses);
• sensors that transform information on physical quantities (position, speed, pressure, temperature, luminosity, etc.) into characteristic electrical signals that they transmit to the control units;
• actuators, electromechanical parts electrically controlled by the engine management unit, which interfere with the operation of the vehicle;
• the control unit, also called computer, module, or unit: this is a programmed electrical unit that, depending on the parameters supplied by the sensors, controls the actuators for the proper operation of the vehicle.

 We can mention the injectors, the EGR valve, the flow regulator, the turbo pressure solenoid valve, etc., for the engine, and the lock actuators for the central locking system…

 Role of the GEM

 The GEM is a supercomputer that manages various functions (electric windows, locking of the opening doors, wiping, signalling, etc.), including the cabin fuses and is also a centralizing and interfacing box.

 The communication system for these various functions is provided by multiplexing, with different communication speeds and languages.

 Good to know: multiplexing is a computer language composed of a binary code allowing the serial circulation of various coded messages (in general, the communication support is the “bus”, consisting of two twisted electrical wires).

 The GEM, therefore, centralizes this information and translates all these different languages for the overall management of the vehicle’s functions.

 Note: Depending on the manufacturer, it will be called the Comfort Control Module at Audi, GEM at Ford, etc., but it is a standard box with the same functions.

Maintenance of the GEM

 The symptoms of a defective box are initially confusing and varied:

• no start-up;
• some functions are affected (a window is lowered unexpectedly or the low beam lights remain on);
• the vehicle adopts a degraded mode of operation (engine speed limitation, accelerated engine speed, etc.)

 Without cause attributable to short circuits, the failure of an ECU is exceptional (replacements are often made wrongly). In most cases, the peripherals are defective (electrical lines, connections, sensors or actuators). Weather conditions, water infiltration, humidity, dust, etc…., a dirty vehicle rarely kept in a garage, and frontal shocks are also among the reasons. Still, sometimes the module becomes faulty even for well-maintained cars (maybe because of old age).

 Good to know: the diagnosis is complex and reserved for qualified technicians: before validating the replacement of the GEM, the validity of all the electrical inputs and outputs must be checked.

 Depending on the technical nature of the system and the manufacturer, the price varies from $700 to $2,000; it is only available through the manufacturer’s network.

 The replacement of the GEM is accompanied by a reset with the manufacturer’s diagnostic tool.

 Note: some companies intervene in the internal electronics of the boxes through two possibilities: repair with an estimate or a standard exchange. If you choose a reputable company, you can save up to 80% on a new box. 

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