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ELECTRONIC ENGINE CONTROL (EEC) SYSTEM

Overview
The electronic engine control (EEC) system provides optimum control of the engine and transmission through the enhanced capability of the PCM. The EEC system also has an on-board diagnostics monitoring system (OBD II with features and functions to meet federal regulations on exhaust emissions).
The EEC system has two major divisions: hardware and software. The hardware includes the PCM, 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. EEC hardware and software are discussed.
This section contains detailed descriptions of the operation of EEC 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 MIL, communicates to the IDS or equivalent tester 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 OBD II VehiclesModifications 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.

Powertrain Control Software
MultiplexingThe increased number of modules on the vehicle dictates a more efficient method of communication. Multiplexing is the process of communicating several messages over the same signal path. This process allows multiple modules to communicate with each other through the signal path (BUS+/BUS-). Modules communicate with the PCM using controller area network (CAN) which determines the priority in which the signals are sent. (See Controller Area Network for more information.) Multiplexing reduces the weight of the vehicle by reducing electrical wiring.Controller Area NetworkThe HS-CAN network uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a bus HS-CAN (+) message is sent. Multiple bus messages can be sent over the network circuits allowing multiple modules to communicate with each other. The HS-CAN is a high speed communication network used for the instrument cluster, the powertrain control module (PCM), the four-wheel drive (4WD) control module, the restraints control module (RCM), and the occupant classification sensor module communications, and designed for real time information transfer and control. The HS-CAN network will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The HS-CAN bus may remain operational when 1 of the 2 termination resistors are not present.Flash Electrically Erasable Programmable Read Only MemoryThe EEPROM is an integrated circuit (IC) within the PCM. This IC contains the software code required by the PCM to control the powertrain. One feature of the EEPROM is that it can be electrically erased and then reprogrammed without removing the PCM from the vehicle.
Manual data entry must be performed if the old module is damaged and/or incapable of communicating. Remove and replace the old PCM. Using the IDS or equivalent tester, select and execute module/parameter reprogramming referring to the manufacturers users manual. Important, make certain that all parameters are included. Failure to properly program tire size in revolutions per mile, (rev/mile = 63,360 divided by the tire circumference in inches) axle ratio, 4WD/2WD, and/or manual/electronic shift on the fly (MSOF/ESOF) may result in codes: P1635, and P1639.Making Changes to the VID BlockA PCM which is programmed may require changes to be made to certain VID information to accommodate vehicle hardware. See PCM/Module Reprogramming on the IDS or equivalent tester.Making Changes to the PCM CalibrationAt certain times, the entire EEPROM will need to be completely reprogrammed. This is due to changes made to the strategy or calibration after production or the need to reset. See PCM/Module Reprogramming on the IDS or equivalent tester.Idle Air TrimIdle air trim is designed to adjust the IAC calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The idle air trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in RAM and retains the learned values even after the engine is shut off. A DTC is output to indicate that the idle air trim has reached its learning limits.
Whenever an IAC component is replaced, cleaned or a service affecting idle is performed, it is recommended that keep alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned idle air trim values.

NOTE:Once keep alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.





Fuel TrimThe fuel control system uses the fuel trim table to compensate for normal variability of the fuel system components caused by wear or aging. During closed loop vehicle operation, if the fuel system appears biased lean or rich, the fuel trim table will shift the fuel delivery calculations to remove the bias. The fuel system monitor has two means of adapting short term fuel trim (FT) and long term fuel trim (FT).
Short term fuel trim (short term FT) (displayed as SHRTFT 1 and SHRTFT2 on the IDS or equivalent tester) is a parameter that indicates short-term fuel adjustments. Short term FT is calculated by the PCM from HO2S inputs and helps maintain a 14.7:1 air/fuel ratio during closed loop operation. This range is displayed in percentage (%). A negative percentage means that the HO2S is indicating RICH and the PCM is attempting to lean the mixture. Ideally, short term FT may remain near 0% but can adjust between -25% to +35%.
Long term fuel trim (long term FT) (displayed as LONGFT1 and LONGFT2 on the IDS or equivalent tester) is the other parameter that indicates long-term fuel adjustments. Long term FT is also referred to as fuel trim. Long term FT is calculated by the PCM using information from the short term FT to maintain a 14.7:1 air/fuel ratio during closed loop operation. The fuel trim strategy is expressed in percentages The range of authority for long term FT is from -35% to +35%. The ideal value is near 0% but variations of +20% are acceptable. Information gathered at different speed load points are stored in fuel trim cells in the fuel trim tables, which can be used in the fuel calculation.
Short term FT and long term FT work together. If the HO2S indicates the engine is running rich, the PCM will correct the rich condition by moving short term FT in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time short term FT is still compensating for a rich condition, the PCM learns this and moves long term FT into the negative range to compensate and allows short term FT to return to a value near 0%.
As the fuel control and air metering components age and vary from nominal values, the fuel trim learns corrections while in closed loop fuel control. The corrections are stored in a table that is a function of engine speed and load. The tables reside in keep alive RAM and are used to correct fuel delivery during open and closed loop. As changing conditions continue the individual cells are allowed to update for that speed load point. If, during the adaptive process, both short term FT and long term FT reach their high or low limit and can no longer compensate, the MIL is illuminated and a DTC is stored.
Whenever a fuel injector or fuel pressure regulator is replaced, keep alive RAM should be cleared. This is necessary so the PCM does not use the previously learned fuel trim values.Failure Mode Effects ManagementFailure mode effects management (FMEM) is an alternate system strategy in the PCM designed to maintain engine operation if one or more sensor inputs fail.
When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine operational strategy.
All FMEM sensors display a sequence error message on the IDS or equivalent tester. The message may or may not be followed by key on, engine off (KOEO) or continuous memory DTCs when attempting the KOER self-test.Engine RPM/Vehicle Speed LimiterThe PCM will disable some or all of the fuel injectors whenever an engine rpm or vehicle overspeed condition is detected. The purpose of the engine rpm or vehicle speed limiter is to prevent damage to the powertrain. The vehicle will exhibit a rough running engine condition, and the PCM will store a continuous memory DTC P1270. Once the driver reduces the excessive speed, the engine will return to the normal operating mode. No repair is required. However, the technician should clear the PCM and inform the customer of the reason for the DTC.
Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in rpm while in NEUTRAL or while driving.

Powertrain Control Hardware
Smart Junction Box (SJB)Keep Alive Random Access Memory (RAM)
The PCM stores information in keep alive RAM (a memory integrated circuit chip) about vehicle operating conditions, and then uses this information to compensate for component variability. Keep alive RAM remains powered when the ignition switch is off so that this information is not lost.Hardware Limited Operation Strategy (HLOS)This system of special circuitry provides minimal engine operation should the PCM [mainly the central processing unit (CPU) or EEPROM] stop functioning correctly. All modes of self-test are not functional at this time. Electronic hardware is in control of the system while in HLOS.

HLOS allowable output functions:

- Spark output controlled directly by the CKP signal
- Fixed fuel pulse width synchronized with the CKP signal
- Fuel pump relay energized
- Idle speed control output signal functional

HLOS disabled outputs to default state:

- EGR solenoids
- No torque converter clutch lock-up

PCM location

- In the engine compartment, at the rear of the engine above the center of the cowl

Integrated Electronic Ignition System

The integrated electronic ignition (EI) system consists of a crankshaft position (CKP) sensor, coil pack(s), connecting wire, and PCM. The coil on plug (COP) integrated EI system uses a separate coil for each spark plug and each coil is mounted directly onto the plug. The COP integrated EI system eliminates the need for spark plug wires but does not require input from the camshaft position (CMP) sensor.

Power and Ground Signals
Vehicle PowerWhen the ignition switch is turned to the START or RUN position, battery positive voltage (B+) is applied to the coil of the electronic engine control (EC) power relay. Since the other end of the coil is wired to ground, this energizes the coil and closes the contacts of the electronic EC power relay. Vehicle power (VPWR) is now sent to the PCM and the electronic EC system as VPWR.Vehicle Reference VoltageThe vehicle reference voltage (VREF) is a positive voltage (about 5.0 volts) that is output by the PCM. This is a consistent voltage that is used by the 3-wire sensors.Mass Air Flow ReturnThe mass air flow return (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 ReturnThe signal return (SIG RTN) is a dedicated ground circuit used by most electronic EC sensors and some other inputs.Power GroundPower ground (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
NOTE:Damaged gold terminals should only be replaced with new gold terminals.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. The electronic EC components equipped with gold terminals will vary by vehicle application.

Continued in Part 2 Part 2
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