Electronic Engine Control (EC) System

Overview
The Electronic Engine Control (Electronic EC) system provides optimum control of the engine and transmission through the enhanced capability of the Powertrain Control Module (PCM). The Electronic EC system also has an on-board diagnostics monitoring system (On Board Diagnostics II) with features and functions to meet federal regulations on exhaust emissions.

The Electronic EC system has two major divisions: hardware and software. The hardware includes the PCM, Natural Gas Vehicle (NGV) module, Constant Control Relay Module (CCRM) sensors, switches, actuators, solenoids, and interconnecting terminals. The software in the PCM provides the strategy control for outputs (engine hardware) based on the values of the inputs to the PCM. Electronic EC hardware and software are discussed at Powertrain Control Software and Powertrain Control Hardware. Powertrain Control Software Powertrain Control Hardware

There are also detailed descriptions of the operation of Electronic EC system input sensors and switches, output actuators, solenoids, relays and connector pins (including other power-ground signals).

The PCM receives information from a variety of sensor and switch inputs. Based on the strategy and calibration stored within the memory chip, the PCM generates the appropriate output. The system is designed to minimize emissions and optimize fuel economy and driveability. The software strategy controls the basic operation of the engine and transmission, provides the OBD II strategy, controls the Malfunction Indicator Lamp (MIL), communicates to the scan tool via the Data Link Connector (DLC), allows for Flash Electrically Erasable Programmable Read Only Memory (EEPROM), provides idle air and fuel trim, and controls Failure Mode Effects Management (FMEM).

The electronic engine controls consist of the:
^ Powertrain Control Module (PCM)
^ Throttle Position (TP) sensor
^ Idle Air Control (IAC) valve
^ Camshaft Position (CMP) sensor
^ Crankshaft Position (CKP) sensor
^ Mass Air Flow (MAF) sensor
^ Heated Oxygen Sensor (HO2S)
^ Knock Sensor (KS)
^ Cylinder Head Temperature (CHT) sensor
^ Clutch Pedal Position (CPP) switch

The PCM needs the following inputs to control the engine correctly:
^ camshaft position
^ engine rpm
^ engine cylinder head temperature
^ amount of engine detonation

The TP sensor:
^ sends the PCM a signal indicating the throttle plate angle.
^ is the main input to the PCM from the driver.

The IAC valve:
^ controls bypass air around the throttle plate at low speeds.
^ is controlled by the PCM.

The CMP sensor:
^ sends the PCM a signal indicating camshaft position used for fuel synchronization and coil firing.

The CKP sensor:
^ sends the PCM a signal indicating crankshaft position.
^ is essential for calculating spark timing.

The MAF sensor:
^ sends the PCM a signal indicating mass airflow rate of air entering the engine.
^ incorporates the Intake Air Temperature (IAT) sensor.

The HO2S:
^ has the ability to create a voltage signal dependent on exhaust oxygen content.
^ provides feedback information to the PCM used to calculate fuel delivery.

The KS:
^ is located top forward of the block under the intake manifold.
^ sends a signal to the PCM indicating engine detonation.

The CHT sensor:
^ is mounted into the wall of the cylinder head and is not connected to any coolant passages.
^ sends a signal to the PCM indicating the cylinder head temperature.
- If the temperature exceeds 126°C (258°F), the PCM disables four fuel injectors at a time. The PCM will alternate which four injectors are disabled every 32 engine cycles. The four cylinders that are not being fuel injected act as air pumps to aid in cooling the engine.
- If the temperature exceeds 154°C (310°F), the PCM disables all of the fuel injectors until the engine temperature drops below 154°C (310°F).

The Clutch Pedal Position (CPP) switch (manual transmission only):
^ sends a signal to the PCM indicating clutch pedal position.

Modifications to On Board Diagnostic (OBD) II Vehicles
Modifications or additions to the vehicle may cause incorrect operation of the OBD II system. Anti-theft systems, cellular telephones and CB radios must be carefully installed. Do not install these devices by tapping into or running wires close to powertrain control system wires or components.