Grand Prix V6-191 3.1L VIN M SFI (1998)
Powertrain Control Module (PCM): Description and Operation
Powertrain Control Module (PCM)
DESCRIPTION
The Powertrain Control Module (PCM) is located underhood in front of the right strut tower near the engine coolant reservoir. It is the control center
of the fuel injection system and constantly looks at the information from various sensors and controls the systems that affect vehicle performance. It
controls the following items:
^
Fuel metering system.
^
Transaxle shifting.
^
Ignition timing.
^
On-board diagnostics for Powertrain functions. It constantly looks at the information from various sensors, and controls the systems that affect
vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through
the Malfunction Indicator Lamp (MIL), and store diagnostic trouble codes which identify the problem areas to aid the technician in making
repairs.
To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC)
spark timing:
^
Ignitions Control module (ICM).
^
Engine Coolant Temperature (ECT) sensor.
^
Intake Air Temperature (IAT) sensor.
^
Mass Air Flow (MAF) sensor.
^
Trans Range inputs from Transaxle Range switch.
^
Throttle Position (TP) sensor.
^
Vehicle Speed Sensor (VSS).
PCM FUNCTION
The PCM supplies either 5 or 12 volts to power various sensors or switches. This is done through resistances in the PCM which are so high in value
that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because
its resistance is too low. Therefore, a digital voltmeter with at least 10 megaohm input impedance is required to ensure accurate voltage readings. Tool
J 39200 meets this requirement. The PCM controls output circuits such as the injectors, IAC, cooling fan relays, etc. by controlling the ground or
power feed circuit through transistors or a device called a Driver.
EEPROM
The Electrically Erasable Programmable Read Only Memory (EEPROM) is a permanent memory that is physically soldered within the PCM. The
EEPROM contains program and calibration information that the PCM needs to control powertrain operation. Unlike the PROM used in certain past
applications, the EEPROM is not replaceable. If the PCM is replaced, the new PCM will need to be programmed. Techline equipment (Tech-2)
containing the correct program and calibration for the vehicle is required to program the PCM.
