Actron GM Code Scanner CP9001 - Manual (Page 33)

33
GLOSSARY
A/C
Air conditioner.
A/C Clutch
relay
The ECM uses this relay to
energize the A/C clutch - to
turn the A/C system on or
off.
A/C On (A/C
Signal)
An input signal to the ECM
indicating that either the A/
C compressor is running or
that A/C operation is being
requested (depends upon
vehicle). Then ECM
adjusts idle speed to
prevent engine stalling
when the A/C system is
engaged. The ECM may
also turn on the engine
cooling fan.
A/C Pressure
sensor
This sensor is connected
to the A/C refrigerant line.
It measures refrigerant
pressure and sends a
voltage signal to the ECM.
The ECM will turn off the
A/C system (by de-
energizing the A/C Clutch
relay) to prevent
compressor damage if the
pressure is too high or low.
A/C Pressure
switch
This is a mechanical switch
connected to the A/C
refrigerant line. The switch is
activated (which sends a
signal to the ECM) when the
A/C refrigerant pressure
becomes too low. The ECM
will turn off the A/C system
(by de-energizing the A/C
Clutch relay) to prevent
compressor damage. Some
vehicles have a second
switch activated when the
refrigerant pressure is too
high.
Actuator
Devices which are
powered by the ECM to
control things. Actuator
types include relays,
solenoids and motors.
Actuators allow the ECM to
control engine operation.
A/F
Air/fuel.
Air Injection
Reaction (AIR)
system
This is an emission control
system operated by the
ECM. During cold engine
warm-up, an air pump
injects outside air into the
exhaust manifold to help
burn hot exhaust gases.
This reduces pollution and
speeds warm-up of oxygen
sensor and catalytic
convertor. After the engine
is warm, the air will either
be “dumped” back to the
atmosphere (or into the air
cleaner) or sent into the
catalytic convertor. There
are various versions of the
AIR system - depends
upon vehicle.
The air pump is usually belt
driven by the vehicle
engine. The ECM controls
air flow from the pump by
operating two electrically
powered solenoid valves.
An Electric Air Divert Valve
either “dumps” the air to
atmosphere (valve
unpowered) or sends the
air further into the system
(valve energized). A
second control valve, the
Air Switching Valve, routs
the air to the catalytic
convertor (valve
unpowered) or to the
exhaust manifold (valve
energized). These two
valves may be individual
components or combined
into one assembly.
The ECM normally sends
air to the catalytic
convertor during warm
engine operation. The ECM
will divert air away from the
convertor to prevent
overheating damage under
certain operating
conditions, such as decel,
high RPM or “rich” air/fuel
conditions.
Some vehicles have an
electrically powered air
pump controlled by the
ECM. This system injects
air into the exhaust
manifold only when the
pump is energized and
running. No air is injected
when the pump is off. (The
air pump does not send air
to the catalytic convertor in
this version.)
ALDL
Assembly Line Diagnostic
Link. This is the connector
that the Code Scanner
plugs into for testing
purposes. The connector is
wired to the ECM, and is
usually located under the
dashboard on the driver’s
side.
BARO
Barometric Pressure
Sensor. (See MAP sensor
for explanation.)
Boost control
solenoid
Used on certain
supercharger equipped
engines. This solenoid is
normally energized by the
ECM. (This allows the
supercharger system to
operate normally.) The
ECM de-energizes the
solenoid during higher
engine speed and load
conditions to reduce boost
pressure.
Brake switch
signal
An input signal to the ECM
indicating that the brake
pedal is being depressed.
Vehicles with Cruise
Control systems monitor
the brake switch to
determine when to engage
(or disengage) the cruise
control function. The brake
switch may also have a
circuit supplying power to
the Torque Convertor
Clutch (TCC) solenoid.
This connection ensures
the TCC solenoid will
disengage when the brake
pedal is depressed (see
TCC definition).