Module, Powertrain Control (Pcm): Operation

The Powertrain Control Module (PCM) is a pre-programmed, microprocessor digital computer. The PCM operates the following:

• fuel system
• regulates ignition timing
• air-fuel ratio
• emission control devices
• charging system
• certain transmission features
• speed control
• air conditioning compressor clutch engagement
• idle speed

The PCM can adapt its programming to meet changing operating conditions. It also receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as PCM Outputs.

The PCM will operate in two different modes:

• Open Loop  - During Open Loop operation, the PCM still receives all input signals but, responds only to a limited amount of inputs based on the algorithms for output control. Inputs from the Oxygen (O2) Sensors and other sensors (depending on the PCM programming) are not monitored during Open Loop modes.
• Closed Loop  - During Closed Loop operation, the PCM will monitor all inputs and outputs. These inputs indicate to the PCM whether or not the calculated output settings results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel.

By monitoring the exhaust oxygen content through the O2 Sensor and all other inputs, the PCM has the ability to fine tune the air handling, fuel control, ignition timing and spark advance settings. This is done to achieve optimum fuel economy combined with low emission engine performance.

The PCM uses the Controller Area Network - Chassis (CAN-C) bus to perform engine diagnostics and flash operations.