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Open Loop (OL):
A control system mode that does not monitor the output to verify if the desired
results were achieved. A fuel delivery system usually operates in open loop
mode during cold engine warm-up because the oxygen sensors are not yet
ready to send a signal. Without the oxygen sensor signal, the computer cannot
check the actual results of combustion.
PCM:
Powertrain Control Module. The brains of the engine and transmission control
systems housed in a metal box with a number of sensors and actuators
connected via a wiring harness. Its job is to control fuel delivery, idle speed,
spark advance timing, and emission systems. The PCM receives information
from sensors, then energizes various actuators to control the engine. The PCM
is also known as the ECM (Engine Control Module).
PCV:
Positive Crankcase Ventilation
Pending Codes:
Also referred to as Continuous Memory codes and Maturing Diagnostic Trouble
Codes. Pending Codes may be set by emission related powertrain components
and systems. If the fault does not occur after a certain number of drive cycles,
the code is erased from memory.
PID:
Parameter Identification. Identifies an address in memory which contains
vehicle operating information.
PNP:
Park/Neutral Position. A switch that tells the PCM when the gear shift lever is
in the Park or Neutral position. When in Park or Neutral, the PCM operates the
engine in an idle mode.
PROM:
Programmable Read-Only Memory. The PROM contains programming
information the PCM needs to operate a specific vehicle model/engine
combination.
Proprietary Readings:
Parameters shown by on-board computers which are not required by OBD II, but
included by manufacturer to assist in trouble-shooting specific vehicles.
PSPS:
Power Steering Pressure Switch
Purge Solenoid:
Controls the flow of fuel vapors from the carbon canister to the intake manifold.
The canister collects vapors evaporating from the fuel tank, preventing them
from escaping to the atmosphere and causing pollution. During warm engine
cruise conditions, the PCM energizes the Purge Solenoid so the trapped vapors
are drawn into the engine and burned.
PTC:
Pending Trouble Code
PWM:
Pulse Width Modulated
PZM:
Platform Zone Module
QDM:
Quad Driver Module
RAM:
Random Access Memory