Fleetwood FWD V8-300 4.9L (1993)
Engine Control Module: Description and Operation
OPERATION
The Powertrain Control Module (PCM) is the control center for the Port Fuel Injection (PFI) system and ignition system. The PCM constantly monitors
information from various data sensors and controls output devices that affect vehicle performance. The computer can control these devices through the
use of Quad Driver Modules (QDM). When the PCM is commanding a device or a component "ON," the voltage potential of the output is low or near
zero volts. When the PCM is commanding a device or component "OFF," the voltage potential of the circuit will be "HIGH," or near 12 volts. The
primary function of the QDM is to supply the ground for the component being controlled. The input information has an interrelation between sensor
output. If one of the input devices fails, such as the oxygen sensor, this could affect more than one of the systems controlled by the computer.
VEHICLE CALIBRATION
To allow one type of PCM to be used for many different vehicles, a device called a Memory-Calibration (MEM-CAL) unit is used. The MEM-CAL is
located inside the PCM and has system calibration information based upon the vehicle's axle ratio, engine, transmission, weight, and other specific
configurations of the vehicle. Since the MEM-CAL unit is unique to specific vehicles, it is important to install the MEM-CAL unit into the new PCM
when servicing. The PCM also has self-diagnostic functions which stores trouble codes and alerts the driver through a warning lamp on the instrument
panel.
