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 in this section.
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 malfunction indicator lamp (MIL), communicates to the WDS or equivalent 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).
Hardware Limited Operation Strategy (HLOS)
This system of special circuitry provides minimal engine operation should the PCM [mainly the central processing unit (CPU) or FEEPROM] 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
- Behind instrument panel (cowl), center to both driver and passenger sides.
The Exhaust Gas Recirculation (EGR) system controls the oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel charge. The combustion chamber temperature is reduced, lowering NOx emissions.
The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the fuel vapor storage canister (located in the rear of vehicle along the frame rail) for storage until the vapors are purged to the engine for burning. The EVAP system uses the Evaporative Emission Monitor to detect all leaks greater than 0.040 inch anywhere in the system.
The Evaporative Emission System Monitor is a PCM on-board strategy designed to test the proper operation of the evaporative emissions system. The monitor tests the system components' functions and the system's ability to flow fuel vapors (hydrocarbons) to the engine (intake manifold). DTCs associated with the evaporative emission system are P0442 and P0455.
The Positive Crankcase Ventilation (PCV) System cycles crankcase gases back through the engine where they are burned. The PCV valve regulates the amount of ventilating air and blow-by gas to the intake manifold and prevents backfire from traveling into the crankcase. The PCV valve should be mounted in a vertical position.
| CAUTION | Do not remove the PCV system from the engine. Removal of the PCV system will adversely affect the fuel economy and engine ventilation and result in shorter engine life. |
The Catalytic Converter and Exhaust systems work together to control the release of harmful engine exhaust emissions into the atmosphere. The engine exhaust gas consists mainly of nitrogen (N), carbon dioxide (CO2) and water vapor (H2O). However, it also contains carbon monoxide (CO), oxides of nitrogen (NOx), hydrogen (H), and various unburned hydrocarbons (HCs). CO, NOx, and HCs are major air pollutants, and their emission into the atmosphere must be controlled.
The exhaust system consists of an exhaust manifold, front exhaust pipe, upstream heated oxygen sensor (HO2S), rear exhaust pipe, downstream HO2S, a muffler and an exhaust tailpipe. The catalytic converter is installed between the front and rear exhaust pipes. Catalytic converter efficiency is monitored by the OBD II system.
Description
All OBD II scan tools display the On-Board System Readiness (OSR) Test. The OSR will display the supported monitors on the vehicle and the status of all monitors (complete or not complete) at that time. Fuel, misfire and comprehensive component monitors run continuously and will always display "CONT" status. Only a PCM reset or a keep alive RAM reset will cause the non-continuous monitors to reinitialize to "NO" status.
Freeze Frame Data allows access to emission-related values from specific generic PIDs. These values are stored the instant an emission-related DTC is stored in Continuous Memory. This provides a snapshot of the conditions that were present when the DTC was stored. Once one set of freeze frame data will remain in memory even if another emission-related DTC is stored, with the exception of Misfire or Fuel System DTCs. Once freeze frame data for Misfire or Fuel System DTC is stored, it will overwrite any previous data, and freeze frame will not be further overwritten. When a DTC associated with the freeze frame is erased or a PCM memory reset is performed, new freeze frame data can be stored again. In the event of multiple emission-related DTCs in memory, always note the DTC for the freeze frame data.
The Output Test Mode (OTM) aids in servicing output actuators associated with the PCM. This mode allows the technician to energize and de-energize most of the system output actuators on command. When entering OTM, the outputs can be turned off and on without activating the fan control. The low and high speed fan control(s) may be turned on separately without energizing the other outputs. This function is supported by the WDS or equivalent and may not be available on all generic scan tools.
As a safety precaution, Output Test Mode will default to its normal state after 10 minutes, after the vehicle is started or after cycling the key off then on.
| WARNING | Safety must be observed when using output test mode: When all outputs are on, the electric fuel pump is briefly energized, so make sure fuel system is intact and is not being serviced at this time. When low speed or high speed fan control(s) are turned on, make sure fan blades are clear of any obstruction. |
All OBD II scan tools support the PCM reset.
The PCM reset allows the scan tool to command the PCM to clear all emission-related diagnostic information. When resetting the PCM, a DTC P1000 will be stored in the PCM until all the OBD II system monitors or components have been tested to satisfy a drive cycle, without any other faults occurring.
The following events occur when a PCM reset is performed
- Clears the number of DTCs.
- Clears the DTCs.
- Clears the freeze frame data.
- Clears diagnostic monitoring test results.
- Resets status of the OBD II system monitors.
- Sets DTC P1000.
Note. This function is performed only after retrieval of continuous DTCs.
ON-BOARD DIAGNOSTIC (OBD) TEST DESCRIPTION
The On-Board Diagnostic (OBD) Test is divided into three special tests: Key On Engine Off Self-Test (KOEO), Key On Engine Running (KOER) Self-Test and Continuous Memory DTCs Self-Test. The OBD test checks the integrity and function of the powertrain control system and outputs the test results when requested by the NGS Tester. It also provides a quick end check of the powertrain control system. It is usually performed at the start of each diagnostic procedure with all the accessories off and is performed at the end of most troubleshooting tests for verification of repair and to make sure no other faults were incurred while servicing a previous fault.
Parameter Identification (PID) Access
The PID mode allows access to certain data values, analog and digital inputs and outputs, calculated values and system status information. This includes analog and digital signal inputs and outputs along with calculated values and system status. There are two types of PID lists available. The first is the Generic OBD II PID list. This is a standard set of PIDs for all manufacturers which all scan tools musts be able to access. The second is a Mazda specific list which can be accessed by the NGS Tester. When accessing any of these PIDs, the values will be continuously updated. For a complete list of all PIDs.
The On-Board Diagnostic (OBD) Test is divided into three special tests: Key On Engine Off Self-Test (KOEO), Key On Engine Running (KOER) Self-Test and Continuous Memory DTCs Self-Test. The OBD test checks the integrity and function of the powertrain control system and outputs the test results when requested by the WDS or equivalent. It also provides a quick end check of the powertrain control system. It is usually performed at the start of each diagnostic procedure with all the accessories off and is performed at the end of most troubleshooting tests for verification of repair and to make sure no other faults were incurred while servicing a previous fault.
The PID mode allows access to certain data values, analog and digital inputs and outputs, calculated values and system status information. This includes analog and digital signal inputs and outputs along with calculated values and system status. There are two types of PID lists available. The first is the Generic OBD II PID list. This is a standard set of PIDs for all manufacturers which all scan tools musts be able to access. The second is a Mazda specific list which can be accessed by the WDS or equivalent. When accessing any of these PIDs, the values will be continuously updated. For a complete list of all PIDs.
DESCRIPTION OF OBD II DRIVE CYCLE
The purpose of the OBD II drive cycle is to execute the OBD II monitors and identify any concerns with the OBD II system. The DTC P1000 code will be erased of all OBD II monitors that have completed during the OBD II drive cycle.
| WARNING | Strict observance of posted speed limits and attention to driving conditions are mandatory when proceeding through the following Drive Cycles. |
The WDS or equivalent will be used to observe the status of each OBD II monitor at the completion of the OBD II drive cycle. The completion status of the exhaust gas recirculation (EGR), heated oxygen sensor (HO2S), evaporative emission (EVAP), and catalyst efficiency monitors can be monitored during the OBD II drive cycle by viewing the On-Board Readiness Menu on the WDS or equivalent.
PINPOINT TEST 4: THE ENGINE COOLING FAN(S) INOPERATIVE/INCORRECT OPERATION
Note. Before carrying out the following test, diagnose any PCM DTCs.
