Engine Control Module: Description and Operation

Powertrain Control Module (PCM):

PURPOSE
The Powertrain Control Module (PCM) is the heart of the Electronic Engine Control-V (EEC-V) system. The PCM receives information from a variety of sensor and switch inputs through it's 104-pin electrical connector.

OPERATION
Based on the strategy and calibration stored within the memory chip, the PCM generates appropriate outputs minimizing emissions, maximizing fuel economy and driveablity. The software method provides the On Board Diagnostics II (OBD II) strategy, controlling Malfunction Indicator Lamp (MIL) operation, communication to the New Generation Star (NGS) scan tool or equivalent through the Standard Corporate Protocol (SCP). The software strategy also provides adaptive idle air and fuel control, Failure Mode Effects Management (FMEM) and allows for Flash Electrically Erasable and Programmable Read-Only-Memory (EPROM). The PCM also has a Hardware Limited Operating Strategy (HLOS) in case the PCM stops functioning and a Keep Alive Memory (KAM).

Standard Corporate Protocol
The SCP is the communication language used for exchanging bi-directional messages (signals) between stand alone modules and devices. Included in these messages is diagnostic data that is output to the Data Link Connector (DLC).

Failure Mode Effects Management
FMEM is a back-up strategy in the PCM designed to maintain vehicle operation if one or more inputs fail. When a sensor input is perceived to be out-of-limits by the PCM, the PCM will substitute a fixed sensor value, continuing to monitor the faulty sensor input. If the faulty sensor begins to again operate within limits, the PCM will return to normal engine running strategy.

Flash Electrically Erasable And Programmable Read-Only-Memory
The EPROM is an Integrated Circuit (IC) within the PCM. This IC contains the software required by the PCM to control the powertrain.
The Flash EPROM can be electrically erased and reprogrammed without removal of the PCM from the vehicle. The reprogramming is accomplished through the DLC.

Hardware Limited Operation Strategy
The HLOS is a system of special circuitry providing minimal engine operation should the PCM stop functioning properly. Electronic hardware is in control of the system while in HLOS.

HLOS allowable output functions:
- Spark output controlled directly by the PIP signal.
- Fixed fuel pulse width synchronized with the PIP signal.
- Fuel pump relay energized.
- Idle Speed Control (ISC) output signal functional.

HLOS disabled outputs to default state:
- Exhaust Gas Recirculation (EGR) solenoids.
- No torque converter lock-up.

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