Electronic Engine Control (EC) System
OverviewThe 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).
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.
Electonic Engine Controls
The electronic engine controls consist of the following:
^ Powertrain Control Module (PCM)
^ Throttle Position (TP) sensor
^ Idle Air Control (IAC) valve
^ Engine Coolant Temperature (ECT) sensor
^ Camshaft Position (CMP) sensor
^ Crankshaft Position (CKP) sensor
^ Mass Air Flow (MAF) sensor
^ Intake Air Temperature (IAT) sensor
^ Heated Oxygen Sensor (HO2S)
^ catalyst monitor sensor
^ wheel speed sensor
^ flex fuel sensor
The PCM:
^ accepts input from various engine sensors to compute the fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operating range.
^ outputs a command to the fuel injectors to meter the appropriate quantity of fuel.
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 ECT sensor:
^ sends the PCM a signal indicating engine temperature.
^ resistance decreases as coolant temperature increases.
The CMP sensor:
^ provides camshaft position information which is used by the PCM for fuel synchronization.
The CKP sensor:
^ sends the PCM a signal indicating crankshaft position.
^ is essential for calculating spark timing.
The MAF sensor:
^ uses a hot wire sensing element to measure the amount of air entering the engine.
^ sends the PCM a signal to determine the intake air mass. The PCM will then calculate the required fuel injector pulse width in order to provide the desired air/fuel ratio.
The IAT sensor:
^ sends the PCM a signal indicating the temperature of the air entering the engine.
^ resistance decreases as temperature increases.
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 catalyst monitor sensor:
^ 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 wheel speed sensor:
^ sends a signal to the PCM indicating wheel speed.
The flex fuel sensor:
^ determines if the engine is using flex ethanol or unleaded gasoline. For additional information, refer to Fuel Delivery and Air Induction.