Part 1
ELECTRONIC ENGINE CONTROL (EEC) SYSTEM
Part 1 of 6
Overview
The 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 (OBD) monitoring system with features and functions to meet federal regulations on exhaust emissions.The EEC system has 2 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. The EEC hardware and software are discussed in this system.This system contains detailed descriptions of the operation of the 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 (FEEPROM), provides idle air and fuel trim, and controls failure mode effects management (FMEM).
Modifications to 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.
Powertrain Control Hardware
PCM
The center of the electronic engine control (EEC) system is a microprocessor called the PCM. The PCM receives input from sensors and other electronic components. Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids, and actuators. The Tribute uses a 150-pin PCM which has 3 separate electrical harness connectors.
PCM Location
The PCM is located behind the instrument panel (cowl), center to both driver and passenger sides (access from the engine compartment).
1. Body
2. Engine
3. Transmission
Fuel Pump Control Module
The fuel pump control module receives a duty cycle signal from the PCM and controls the fuel pump operation in relation to this duty cycle. The PCM requests low or high speed fuel pump operation depending on engine fuel demand. The fuel pump control module controls the fuel pump by switching the fuel pump power circuit on and off at the required duty cycle. The fuel pump control module sends diagnostic information to the PCM on the fuel pump monitor circuit. See Fuel Systems.
Fuel Pump Driver Module (FPDM)
The FPDM receives a duty cycle signal from the PCM and controls the fuel pump operation in relation to this duty cycle. This results in variable speed fuel pump operation. The FPDM sends diagnostic information to the PCM on the fuel pump monitor circuit. For additional information on the fuel pump control and the fuel pump monitor.
Keep Alive Memory (KAM)
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. KAM remains powered when the key 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 electronically erasable programmable read only memory (EEPROM), stop functioning correctly. All modes of self-test are not functional at this time. The electronic hardware is in control of the system while in HLOS.
HLOS Allowable Output Functions:
- Spark output controlled directly by the crankshaft position (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:
- Exhaust gas recirculation (EGR) solenoids
- No torque converter clutch lock-up
Power and Ground Signals
Electronic Throttle Control Reference Voltage (ETCREF)
ETCREF is a consistent positive voltage (5.0 volts plus or minus 0.5 volt) supplied by the PCM. ETCREF is internally bussed within the PCM and is specifically dedicated to the accelerator pedal position (APP) sensor and the electronic throttle body (ETB) throttle position (TP) sensor.
Electronic Throttle Control Return (ETCRTN)
ETCRTN is a return path for ETCREF and is internally bussed within the PCM. ETCRTN is specifically dedicated to the APP sensor and the ETB TP sensor.
Gold Plated Pins
NOTE:Gold plated terminals should only be replaced with new gold plated 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.
Keep Alive Power (KAPWR)
KAPWR provides a constant voltage input independent of ignition switch state to the PCM. This voltage is used by the PCM to maintain the keep alive memory (KAM).
Mass Air Flow Return (MAF RTN)
The 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.
Power Ground (PWR GND)
The PWR GND circuit(s) is directly connected to the battery negative terminal. PWR GND provides a return path for the PCM vehicle power (VPWR) circuits.
Signal Return (SIG RTN)
The signal return (SIG RTN) is a dedicated ground circuit used by most electronic EC sensors and some other inputs.
Vehicle Buffered Power (VBPWR)
The VBPWR is a PCM-supplied power source that supplies regulated voltage (10 to 14 volts) to vehicle sensors that run off 12 volts but cannot withstand VPWR voltage variations. It is regulated to VPWR minus 1.5 volts and is voltage limited to protect the sensors.
Vehicle Power (VPWR)
When the key is turned to the ON or START position, battery positive voltage (B+) is applied to the coils of the EEC power relay and power sustain relay (PSR). Since the other end of the coils are wired to ground, this energizes the coils and closes the contacts of the EEC power relay and PSR. VPWR is now supplied to the PCM and the EEC system as VPWR. When the key is turned to the OFF position, the PCM keeps the PSR energized until the normal power-down sequence is completed. See Engine Control Components, Power Sustain Relay.
Vehicle Reference Voltage (VREF)
VREF is a consistent positive voltage (5.0 volts ± 0.5) provided by the PCM. VREF is typically used by 3-wire sensors and some digital input signals.
Powertrain Control Software
Communications
The vehicle has 2 module communication networks: one high speed and one medium speed controller are network (CAN), which are comprised of unshielded twisted pair cable. Both networks are connected to the data link connector (DLC). See Communications Network.
Deceleration Fuel Shut-Off (DFSO)
During a DFSO event the PCM disables the fuel injectors. A DFSO event occurs during closed-throttle deceleration; similar to exiting a freeway. This strategy improves fuel economy, allows for increased rear heated oxygen sensor (HO2S) concern detection, and allows for misfire profile correction learning.
Engine RPM/Vehicle Speed Limiter
The PCM disables some or all of the fuel injectors whenever an engine RPM or vehicle over speed condition is detected. The purpose of the engine RPM or vehicle speed limiter is to prevent damage to the powertrain. The vehicle exhibits a rough running engine condition, and the PCM stores one of the following continuous memory DTCs: P0219, P0297, or P1270. Once the driver reduces the excessive speed, the engine returns to the normal operating mode. No repair is required. However, the technician should clear the DTCs 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.
Fail-Safe Cooling Strategy
The fail-safe cooling strategy is activated by the PCM only in the event that an overheating condition has been identified. This strategy provides engine temperature control when the cylinder head temperature exceeds certain limits. The cylinder head temperature is measured by the cylinder head temperature (CHT) sensor.
A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components may occur. Along with a CHT sensor, the fail-safe cooling strategy is used to prevent damage by allowing air-cooling of the engine. This strategy allows the vehicle to be driven safely for a short period of time when an overheat condition exists.
The engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When the fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders.
Failure Mode Effects Management
Failure 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 determined to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value for the incorrect input and continues to monitor the suspect sensor input. If the suspect sensor begins to operate within limits, the PCM returns to the normal engine operational strategy.
All FMEM sensors display a sequence error message on the scan tool. The message may or may not be followed by key on engine off (KOEO) or continuous memory DTCs when attempting key on engine running (KOER) self-test mode.
Flash Electrically Erasable Programmable Read Only Memory (EEPROM)
The flash 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. If a software change is required to the PCM, a new module is no longer necessary as the current one can be reprogrammed through the data link connector (DLC).
Fuel Trim
Short Term Fuel Trim
If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM enters closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy continuously adjusts the desired air/fuel ratio between rich and lean causing the oxygen sensor to switch around the stoichiometric point. If the time between rich and lean switches are the same, then the system is actually operating at stoichiometric. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometric is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is between -25% and 25%. Some calibrations have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometric. This practice is referred to as using bias. For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce oxides of nitrogen (NOx).
Values for SHRTFT1 and 2 may change significantly on a diagnostic tool as the engine is operated at different RPM and load points. This is because SHRTFT1 and 2 reacts to fuel delivery variability that changes as a function of engine RPM and load. Short term fuel trim values are not retained after the engine is turned off.
Long Term Fuel Trim
While the engine is operating in closed loop fuel control, the short term fuel trim corrections are learned by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in the keep alive memory (KAM) fuel trim tables. Fuel trim tables are based on engine speed and load and by bank for engines with 2 heated oxygen sensor (HO2S) forward of the catalyst. Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include:
- Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop
- Long term fuel trim corrections can be used both while in open loop and closed loop modes
Long term fuel trim is represented as a percentage, similar to the short term fuel trim, however it is not a single parameter. A separate long term fuel trim value is used for each RPM/load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature, and fuel quality (% alcohol, oxygenates). When viewing the LONGFT1/2 PIDs, the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PIDs display the long term fuel trim correction that is currently being used at that RPM/load point.
High Speed Controller Area Network (CAN)
High speed CAN is a serial communication language protocol used to transfer messages (signals) between electronic modules or nodes. Two or more signals can be sent over one CAN communications network circuit allowing 2 or more electronic modules or nodes to communicate with each other. This communication or multiplexing network operates at 500kB/sec (kilobytes per second) and allows the electronic modules to share their information messages.
Included in these messages is diagnostic data that is outputted over the CAN + and CAN - lines to the DLC. PCM connection to the DLC is typically done with a 2-wire, twisted pair cable used for the network interconnection. The diagnostic data such as self-test or PIDs can be accessed with a scan tool.
Idle Air Trim
Idle air trim is designed to adjust the idle calibration to correct for wear and aging of components. When the 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 the idle speed. The table is stored in the KAM and retains the learned values even after the engine is shut off. A DTC is set if the idle air trim has reached its learning limits.
Whenever a component is replaced, or a repair affecting idle is carried out, it is recommended that the KAM be reset. This is necessary so the idle strategy does not use the previously learned idle air trim values.
To reset the KAM, see RESETTING KEEP ALIVE MEMORY (KAM). It is important to note that erasing DTCs with a scan tool does not reset the idle air trim table.
Once the KAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality improves as the strategy adapts. Adaptation occurs in 4 separate modes as shown in the following table.IDLE AIR TRIM LEARNING MODES
ISO 14229 DTC
The ISO 14229 is a global, diagnostic communication standard. ISO 14229 is a set of standard diagnostic messages that can be used to diagnose any vehicle module in use and at the assembly plant. ISO 14229 is similar to the Society of Automotive Engineers (SAE) J2190 diagnostic communication standard that was used by all OEMs for previous communication protocols, like J1850 standard corporate protocol (SCP).
ISO 14229 changes the way PIDs, DTCs, and output state control (OSC) is processed internally in the PCM and in the scan tool software. Most of the changes are to make data transfer between electronic modules more efficient, and the amount and type of information that is available for each DTC. This information may be helpful in diagnosing driveability concerns.
Continued in Part 2 Part 2