Saturday, November 16, 2013
What Is C3 on a GMC
C3, also abbreviated CCC, stands for Computer Command Control. For GMC and all General Motors vehicles predating 1996, the C3 system encompasses a vehicles Electronic Control Module and the engine-related diagnostic system.
First Generation On-Board Diagnostics
In 1996, the Environmental Protection Agency made vehicle diagnostics standard for all makes and models. Before this policy became law, automotive manufacturers used their own unique diagnostic systems. For all General Motors vehicles, the process of access trouble codes differs among Fords, Chryslers and other vehicles. Collectively, this is now known as OBD-I. Everything after 1996 operates under OBD-II standards.
C3 Flash Codes
Once a GMC vehicles ECM detects a problem, a diagnostic trouble code is created. Accessing these codes requires putting the GMC into a self-testing procedure. This can be done by connection the "A" and "B" slots on the GMCs data outlet, which is located directly beneath the steering wheel. Once the ignition key is turned to "On," the codes will be relayed through a flashing check engine light.
Deciphering Flash Codes
General Motors flash codes are numbers comprised of two characters. The first number is represented by a long flash, and the second number is conveyed with shorter flashes. For example, GM code 26 will be two flashes followed by six brief flashes. Code 12 is flashed at the beginning of a self-testing procedure. It does not correspond with a diagnostic problem.
Looking up GM Flash Codes
The system will flash only the codes themselves. When using the self-test procedure, an owner will need to locate definitions for General Motors flash codes. These definitions can be found easily online (See Resources). However, a GMC-focused Haynes or Chilton repair manual also will contain the needed definitions. A GMC owners manual will not feature these definitions.
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