Engine Control Module: Description and Operation

Powertrain COntrol Module:

DESCRIPTION
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is the control center of the vehicle. It controls the following:

^ Fuel metering system.
^ Transmission shifting.
^ Ignition timing.
^ On-board diagnostics for powertrain functions.


OPERATION
The PCM 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. The PCM also alerts the driver through the MIL (Malfunction Indicator Lamp). When the PCM detects a malfunction, it stores a diagnostic trouble code (DTC). A DTC stored, will identify the problem areas. This will aid the technician in' making repairs.

COMPONENTS
The PCM consists of two parts: a controller (the PCM without the Knock Sensor module) and the Knock Sensor module.

The PCM supplies either 5 or 12 volts to power various sensors or switches. This is done through resistances in the PCM. The resistance is 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 (J 39200) with at least 10 megohms input impedance is required to ensure accurate voltage readings.

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 an Output Driver Module.

EEPROM
The Electronically 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 past applications, the EEPROM is not replaceable. If the PCM is replaced, the new PCM will need to be programmed. Techline equipment containing the correct program and calibration for the vehicle, is required to program the PCM.

LEGEND
(1) Powertrain Control Module (PCM)
(2) PCM Connector C3 (Gray/Clear)
(3) Knock Sensor Module Access Cover
(4) PCM Connector C4 (Blue)
(5) PCM Connector C2 (Black)
(6) PCM Connector C1 (Red)