Engines Mechanical and
Power steering relies on a simple principle- a hydraulic pump running off a belt driven by the
engine places a small amount of fluid under pressure, which in turn assists the steering
mechanism in directing the tires as you turn the steering wheel. The system typically includes a
pump, a pressure hose assembly, a control valve, and a return line.
Powertrain Control Module
The PCM is designed to maintain exhaust emission levels to Federal/California/other standards
while providing excellent driveability and fuel efficiency. The PCM monitors numerous engine and
Secondary Air Injection System (A.I.R.)
The Secondary Air Injection (AIR) System reduces exhaust emissions following initial engine start
up. The powertrain control module (PCM) activates the AIR system by suppling a ground to the
AIR pump relay and AIR solenoid relay simultaneously. This action closes the internal contacts of
the AIR pump relay.
PCV Valve (Positive Crankcase Ventilation)
A crankcase ventilation system is used to consume crankcase vapors in the combustion process
instead of venting them to atmosphere. Fresh air from the throttle body is supplied to the
Click on the links above for information on some of the different GM vehicle systems.
From engine mechanical, to electrical, to body control systems.
ABS - Stands for Anti-lock Brakes. If wheel slip is detected by the computer, the ABS system pulses the brake
pressure to the wheels. Many parts make up this system. A computer, sensors, motors, wiring, valves.
Airbags - Supplemental Inflatable Restraint - Also know as SIR. Very important safety item used in
conjunction with the seat belts system. Air bags are in more and more places in todays cars and trucks. Not
only in the steering wheel and passenger front dash, but also in the side pillars next to the front seats, in the
side of the seats, above your head- called curtain air bags, rear occupant side air bags.
Diagnostic computer scan tools - There are many types of scan tools. From the most basic models
you can purchase at most auto parts stores, to the most high-end, cutting edge tools we use at the shop.
These are invaluable tools to diagnose almost any system in todays vehicles. Depending on the capability of
the scanner, you can read trouble computer trouble codes when the check engine light has come on
with the most basic scanner, and manipulating and controlling most vehicle system for testing operation and
diagnostic purposes on the most advanced and expensive types.
Basic electrical theory - Most conventional vehicles use a 12 volt negative ground electrical system.
The battery is the main component that is used to start the vehicle. The alternator is used to supply power to
the cars electrical systems and to keep the battery charged. Testing electrical circuits is done with a Digital
volt Ohm Meter (DVOM).
Displacement on Demand - Provides maximum fuel economy under light load driving conditions. The
engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy
Engine Data Sensors - There are many sensors on todays vehicles to monitor all aspects of engine
operations. From the fuel system, spark control, electronic throttle, engine timing, to emissions controls.
Exhaust Gas recirculation - Known as EGR. This is a very important component in the vehicle emissions
system that has been around for decades in various forms.
Fuel Injection - High pressure fuel is supplied by an electric pump in the fuel tank. Pressure is regulated
by the fuel pressure regulator. The fuel injector is a solenoid operated device, controlled by the Powertrain
Control Module (PCM), that meters pressurized fuel to a single engine cylinder.
Front and Rear Brake Operation
The hydraulic brake system consists of the following:
Hydraulic Brake Master Cylinder Fluid Reservoir: Contains supply of brake fluid for the hydraulic
The electronic ignition system produces a high energy spark. This spark is used to ignite the
compressed air/fuel mixture at the correct time. This provides optimal performance, fuel economy,
and control of exhaust emissions. The cylinder that is at TDC of the compression stroke is called the
event cylinder. The cylinder that is at TDC of the exhaust stroke is called the waste cylinder. The EI
system consists of the following components:
Stability or Stabililtrak System
The vehicle stability enhancement system (VSES) provides added stability during aggressive maneuvers.
Yaw rate is the rate of rotation about the vehicle's vertical axis. The system is activated when the electronic
brake control module (EBCM) determines that the desired yaw rate does not match the actual yaw rate as
measured by the yaw rate sensor.
The evaporative emission System (EVAP)
This control system limits the fuel vapors from escaping into the atmosphere. The EVAP transfers
the fuel vapors from the sealed fuel tank to an activated carbon storage device, the EVAP canister.
The EVAP canister stores the vapors until the engine is able to use the extra fuel vapor. When the
engine is able to use the extra fuel vapor, the intake air flow purges the fuel vapor from the carbon
element and then the normal combustion process consumes the fuel vapor.
Learn how these new High Intensity Discharge lights work. Replace your old halogen bulbs yourself
with these step-by-step instructions.
Automotive Systems Description And Operation Index
Radio Shows LOC or INOP
Learn how the radio theft system works on your car or truck. Get the code
to unlock your radio.