Engine Control Module: Description and Operation

POWERTRAIN CONTROL HARDWARE

Powertrain Control Module (PCM)
The center of the electronic engine control (EEC) system is a microprocessor called the PCM. The PCM receives input from sensors and other electronic components. Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids, and actuators. The hybrid vehicle uses a 190-pin PCM which has three separate electrical harness connectors.

PCM Location
The PCM is located in the engine compartment, driver side, mounted to the cowl between the transmission and the cowl.












Powertrain Control Module (PCM) Keep Alive Memory (KAM)
The PCM stores in KAM (a memory integrated circuit chip) information about vehicle operating conditions, and then uses this information to compensate for component variability. KAM remains powered when the ignition is off so this information is not lost.

Powertrain Control Module (PCM) Power and Ground Signals

Vehicle Buffered Power (VBPWR)
The VBPWR is a PCM-supplied power source that supplies regulated voltage (10 to 14 volts) to vehicle sensors that run off 12 volts but cannot withstand VPWR voltage variations. It is regulated to VPWR minus 1.5 volts and is voltage limited to protect the sensors.

Vehicle Power (VPWR)
VPWR is the primary source of PCM power. VPWR is switched through the PCM power relay and is controlled by the PCM.

Reference Voltage (VREF)
The VREF is a positive voltage (about 5 volts) that is output by the PCM. This is a consistent voltage that is used by the three-wire sensors.

Mass Air Flow Return (MAF RTN)
The MAF RTN is a dedicated analog signal return from the mass air flow (MAF) sensor. It serves as a ground offset for the analog voltage differential input by the MAF sensor to the PCM.

Signal Return (SIG RTN)
The SIG RTN is a dedicated ground circuit used by most EEC sensors and some other inputs.

Power Ground (PWR GND)
The PWR GND is an electric current path return for VPWR voltage circuit. The purpose of the PWR GND is to maintain sufficient voltage at the PCM.

Gold Plated Pins
Some engine control hardware has gold plated pins on the connectors and mating harness connectors to improve electrical stability for low current draw circuits and to enhance corrosion resistance. Replace damaged gold terminals with new gold terminals.