Engine Controls - Description & Operation (Except Diesel & Hybrid): Overview Ford Focus II

Overview

The EEC system provides optimum control of the engine and transmission through the enhanced capability of the powertrain control module (PCM). The EEC system also has an on-board diagnostics (OBD) monitoring system with features and functions to meet federal regulations on exhaust emissions.

Some vehicle applications use a stand-alone transmission control module (TCM). While still part of the EEC system the TCM communicates to the PCM, anti-lock brake system (ABS) module, instrument cluster, and four-wheel drive (4WD) control modules using the high speed controller area network (CAN) communications network. The TCM incorporates a stand alone OBD-II system. The TCM independently processes and stores fault codes, freeze frame, support PIDs as well as J1979 Mode 09 CALID and calibration verification number. The TCM does not directly illuminate the malfunction indicator lamp (MIL), but request the PCM to do so. The TCM is located inside the transmission assembly. It is not repairable, with the exception of reprogramming.

Below is a list of transmissions that use a TCM

1. AWF21 (FWD) 6-speed automatic transmission
2. FNR5 (FWD) transmission
3. F21 (FWD) transmission
4. ZF CFT30 (FWD) continuously variable transmission (CVT)
5. ZF 6HP26 (RWD) transmission
6. ZF 6R (RWD)
7. 6R60 (RWD)

For additional information on these transmissions and TCM diagnostics, refer to the appropriate AUTOMATIC TRANSMISSION article .

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 article.

This article 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). For additional information on the input sensors and output actuators, refer to ENGINE CONTROL COMPONENTS .

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 strategy, controls the MIL, communicates to the diagnostic 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).

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

1. spark output controlled directly by the CKP signal
2. fixed fuel pulse width synchronized with the CKP signal
3. fuel pump relay energized
4. idle speed control output signal functional

HLOS Disabled Outputs To Default State

1. EGR solenoids
2. no torque converter clutch lock-up

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 (CO 2 ) and water vapor (H 2 O). However, it also contains carbon monoxide (CO), oxides of nitrogen (NO x ), hydrogen (H), and various unburned hydrocarbons (HCs). The major air pollutants of CO, NO x , and HCs, and their emission into the atmosphere must be controlled.

The exhaust system generally consists of an exhaust manifold, front exhaust pipe, front heated oxygen sensor (HO2S), rear exhaust pipe, catalyst HO2S, a muffler, and an exhaust tailpipe. The catalytic converter is typically installed between the front and rear exhaust pipes. On some vehicle applications, more than one catalyst is used between the front and rear exhaust pipes. Catalytic converter efficiency is monitored by the on-board diagnostic (OBD) system strategy in the PCM. For information on the OBD catalyst monitor, refer to the description for the CATALYST EFFICIENCY MONITOR .

The number of HO2Ss used in the exhaust stream and the location of these sensors depend on the vehicle emission certification level (LEV, LEV-II, ULEV, PZEV). On most vehicles only 2 HO2Ss are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst are used for primary fuel control while the ones after the catalyst (HO2S12/HO2S22) are used to monitor catalyst efficiency. However, some partial zero emission vehicles (PZEV) use 3 HO2Ss for each engine bank. The stream 1 sensors (HO2S11/HO2S21) located before the catalyst are used for primary fuel control, the stream 2 sensors (HO2S12/HO2S22) are used to monitor the light-off catalyst, and the stream 3 sensors (HO2S13/HO2S23) located after the catalyst are used for long term fuel trim control to optimize catalyst efficiency (fore aft oxygen sensor control). Current PZEV vehicles use only a 4-cylinder engine, so only the bank 1 HO2Ss are used.

Scheme 2

Scheme 3

The dual-injection fuel delivery system consists of a fuel select switch (FSSW) circuit, the fuel rails, the fuel injectors, and a fuel injector interface module.

The fuel injector interface module controls the fuel injectors according to the demand from the powertrain control module (PCM). The fuel injector interface module enables the primary (forward) fuel injectors when in single-injection mode and enables both the primary (forward) and secondary (rearward) fuel injectors when in dual-injection mode. The injection mode is requested by the PCM through the FSSW circuit. The fuel injector interface module communicates the fuel injection mode status to the PCM on the communications network.

The 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 EVAP canister for storage until the vapors are purged to the engine for burning.

All applications required to meet on-board diagnostics (OBD) regulations use the enhanced EVAP system. Some applications also incorporate an on-board refueling vapor recovery (ORVR) system. Refer to the appropriate EVAPORATIVE EMISSIONS article for vehicle specific information.

The EGR system controls the oxides of nitrogen (NO x ) 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 NO x emissions.

The EEGR system uses exhaust gas recirculation to control the oxides of nitrogen (NO x ) emissions just like vacuum operated systems. The only difference is the way in which the exhaust gas is controlled.

The EEGR system consists of an electric motor/EGR valve integrated assembly, a powertrain control module (PCM), and connecting wiring. Additionally a manifold absolute pressure (MAP) sensor is also required. For additional information on the EGR system components, refer to ENGINE CONTROL COMPONENTS . Operation of the system is as follows

Scheme 4

1. The EEGR system receives signals from the engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor, throttle position (TP) sensor, mass air flow (MAF) sensor, crankshaft position (CKP) sensor, and the MAP sensor to provide information on engine operating conditions to the PCM. The engine must be warm, stable, and running at a moderate load and RPM before the EEGR system is activated. The PCM deactivates the EEGR during idle, extended wide open throttle (WOT), or whenever a concern is detected in an EEGR component or EGR required input.
2. The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
3. The PCM in turn outputs signals the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor directly actuates the EEGR valve, independent of engine vacuum. The EEGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to fully open position. The position of the EGR valve determines the EGR flow.
4. A MAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into the intake manifold. Variations in EGR being used correlate to the MAP signal (increasing EGR increases manifold pressure values).

The ESM is an updated differential pressure feedback EGR (DPFE) system. It functions in the same manner as the conventional DPFE system, however the various system components have been integrated into a single component called the ESM. For additional information on the ESM system components, refer to ENGINE CONTROL COMPONENTS . The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the measuring orifice. This arrangement increases system reliability, response time, and system precision. By relocating the EGR orifice from the exhaust to the intake side of the EGR valve, the downstream pressure signal measures manifold absolute pressure (MAP). The system provides the powertrain control module (PCM) with a differential DPFE signal, identical to a traditional DPFE system.

First, the DPFE sensor input circuit is checked for out of range values (P0405 or P0406). The EGR vacuum regulator (EVR) output circuit is checked for opens and shorts (P0403).

The EGR system normally has large amounts of water vapor that are the result of the engine combustion process. During cold ambient temperatures, under some circumstances, water vapor can freeze in the DPFE sensor, hoses, as well as other components in the EGR system. In order to prevent malfunction indicator lamp (MIL) illumination for temporary freezing, the following logic is used.

If an EGR system concern is detected below 0°C (32°F), only the EGR system is disabled for the current driving cycle. A diagnostic trouble code (DTC) is not stored and the I/M readiness status for the EGR monitor does not change. The EGR monitor, however, continues to operate. If the EGR monitor determines that the concern is no longer present, the EGR system is enabled and normal system operation is restored.

If an EGR system concern is detected above 0°C (32°F), the EGR system and the EGR monitor is disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the concern has been detected on 2 consecutive driving cycles.

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check is carried out. Since the EGR system is a closed loop system, the EGR system delivers the requested EGR flow as long as it has the capability to do so. If the EVR duty cycle is very high (greater than 80% duty cycle), the differential pressure indicated by the DPFE sensor is evaluated to determine the amount of EGR system restriction. If the differential pressure is below a calibrated threshold, a low flow concern is indicated (P0401/P0406).

Finally, the differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR flow to carry out the high flow check. If the differential pressure exceeds a calibrated limit, it indicates a stuck open EGR valve or debris temporarily lodged under the EGR valve seat (P0402).

If the inferred ambient temperature is less than 0°C (32°F), or greater than 60°C (140°F), or the altitude is greater than 8,000 feet (BARO less than 22.5 in-Hg), the EGR monitor cannot be run reliably. In these conditions, a timer starts to accumulate the time in these conditions. If the vehicle leaves these extreme conditions, the timer starts to decrement, and, if conditions permit, attempts to complete the EGR flow monitor. If the timer reaches 800 seconds, the EGR monitor is disabled for the remainder of the current driving cycle and the EGR monitor I/M readiness bit is set to a ready condition after one such driving cycle. Vehicles require 2 such driving cycles for the EGR monitor to be set to a ready condition.

The fuel system supplies the sequential multiport fuel injection (SFI) fuel injectors with clean fuel at a controlled pressure. The powertrain control module (PCM) controls the fuel pump and monitors the fuel pump circuit. The PCM controls the fuel injector on/off cycle duration and determines the correct timing and amount of fuel delivered. When a new fuel injector is installed it is necessary to reset the learned values contained in the keep alive memory (KAM) in the PCM. Refer to RESETTING THE KEEP ALIVE MEMORY (KAM) .

The 2 types of fuel systems used are

1. electronic returnless fuel
2. mechanical returnless fuel

The ignition system is designed to ignite the compressed air/fuel mixture in an internal combustion engine by a high voltage spark from an ignition coil. The ignition system also provides engine timing information to the powertrain control module (PCM) for correct vehicle operation and misfire detection.

The intake air system provides clean air to the engine, optimizes air flow, and reduces unwanted induction noise. The intake air system consists of an air cleaner assembly, resonator assemblies, and hoses. Some vehicles use a hydrocarbon filter trap to help reduce emissions by preventing fuel vapor from escaping into the atmosphere from the intake when the engine is off. It is typically located inside the air intake system. The mass air flow (MAF) sensor is attached to the air cleaner assembly and measures the volume of air delivered to the engine. The hydrocarbon trap is part of the EVAP system. For more information on the EVAP system, refer to EVAPORATIVE EMISSION (EVAP) SYSTEMS . The MAF sensor can be replaced as an individual component. The intake air system also contains a sensor that measures the intake air temperature (IAT), which is also integrated with the MAF sensor. For additional information on the intake air system components, refer to ENGINE CONTROL COMPONENTS . Air induction resonators can be separate components or part of the intake air housing. The function of a resonator is to reduce induction noise. The air induction components are connected to each other and to the throttle body assembly with hoses.

Scheme 5

Throttle Body System Overview

Note. This overview is for applications without electronic throttle control (ETC). For ETC applications, refer to TORQUE BASED ELECTRONIC THROTTLE CONTROL (ETC) .

Note. The traditional idle air adjust procedure and the throttle return screw are no longer used on OBD applications.

The throttle body system meters air to the engine during idle, part throttle, and wide open throttle (WOT) conditions. The throttle body system consists of an idle air control (IAC) valve assembly, an idle air orifice, single or dual bores with butterfly valve throttle plates, and a throttle position (TP) sensor. One other source of idle air flow is the positive crankcase ventilation (PCV) system. The combined idle air flow (from idle air orifice IAC flow and PCV flow) is measured by the MAF sensor on all applications.

During idle, the throttle body assembly provides a set amount of air flow to the engine through the idle air passage and the PCV valve. The IAC valve assembly provides additional air when commanded by the PCM to maintain the correct engine idle speed under varying conditions. The IAC valve assembly mounts directly to the intake manifold assembly in most applications. Idle speed is controlled by the PCM and cannot be adjusted.

Throttle rotation is controlled by a cam/cable linkage to slow the initial opening rate of the throttle plate. The TP sensor monitors the throttle position and provides a signal to the PCM. Some throttle body applications provide an air supply channel upstream of the throttle plate to provide fresh air to the PCV or IAC systems. Other throttle body applications provide individual vacuum taps downstream of the throttle plate for PCV return, exhaust gas recirculation (EGR), evaporative emission (EVAP), and miscellaneous control signals.

Overview of the Intake Manifold Runner Control (IMRC) and Intake Manifold Tuning Valve (IMTV) Systems

There are 3 basic types of intake air sub-systems

1. IMRC electric actuated system
2. IMRC vacuum actuated system
3. IMTV

There are several different styles of hardware used to control airflow within the engine air intake system. In general, the devices are defined based on whether they control in-cylinder motion (charge motion) or manifold dynamics (tuning).

The IMRC is a charge motion device that modifies the air charge motion in the manifold. The IMRC control valve is located close to the intake valve/cylinder head. The IMRC actuator can be either electric or vacuum controlled. The IMRC system must have a monitor feedback system in order to meet OBDII regulations.

The IMTV is a manifold tuning device that effects the air flow volume of the manifold by connecting multiple plenums or inlets within the manifold system. The IMTV control valve is located in the center of the intake manifold away from the intake valve or cylinder head. The IMTV actuator can be either electric or vacuum controlled. The IMTV system does not have to be monitored for OBDII regulations.

Some vehicles may use both systems.

These subsystems are used to provide increased intake airflow to improve torque, emissions and performance. The overall volume of air metered to the engine is controlled by the throttle body. Vehicles equipped with electronic throttle control (ETC) does not use an idle air control (IAC).

The PCV system cycles crankcase gases back through the induction system into the engine where they are burned. The PCV valve regulates the amount of ventilated air and blow-by gases to the intake manifold.

Currently, both heated and non-heated PCV systems are used. The heated systems use either a water heated valve, an electrically heated valve, or an electrically heated tube. Engine coolant flows around the water heated valve to prevent it from freezing. Electrically heated systems use a heating element enclosed in the PCV valve or the PCV tube to prevent the valve or tube from freezing. The valve or the tube heater can be controlled by either the PCM or the thermal harness.

1. Thermal harness controlled heater - On vehicle applications that are equipped with a thermal harness to the PCV valve or tube. The thermal harness only provides electrical continuity to the heating element when temperatures are less than 5°C +/- 4°C (40°F +/- 7°F). Typically this harness is located close to the PCV valve or tube.
2. PCM controlled heater - On these applications the PCV heater is turned on by the PCM. When the intake air temperature is less than 0°C (32°F) the PCM grounds the positive crankcase ventilation valve heater control (PCVHC) circuit and turns the heater ON. When the intake air temperature exceeds 9°C (48°F) the heater is turned OFF. The PCV heater is also OFF when the engine is not running to prevent unnecessary battery drain. The heater is also OFF if the vehicle charging system is greater than 16 volts. This minimizes heater element overload.

PCV systems that comply with OBD PCV monitoring requirements use a quarter-turn cam-lock thread design at one end to prevent accidental disconnection from the valve cover. For more information about the PCV monitor refer to POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM MONITOR .

Note. When the battery (or PCM) is disconnected and connected, some abnormal drive symptoms may occur while the vehicle relearns its adaptive strategy. The charging system set point may also vary. The vehicle may need to be driven to relearn its strategy.

The PCM-controlled charging system provides many additional benefits over the current integral generator regulator system. The first benefit is improved battery life. In an integral generator regulator system, the regulator set point is established by a temperature sensor in the regulator which estimates battery temperature. In a PCM-controlled charging system, the regulator voltage set point is determined by the PCM and communicated to the regulator through the generator regulator control (GENRC) circuit. The PCM uses an algorithm to estimate battery temperature. Improving battery temperature estimates reduces battery damage caused by over- and undercharging.

The second benefit is improved engine performance. Whenever the PCM senses a wide open throttle (WOT) condition, the PCM momentarily lowers the regulator voltage set point. This reduces the torque load of the generator on the engine and improves acceleration. The PCM has a calibratable time limit on this reduced voltage feature. This is to prevent the generator output from being cut back for an extended WOT period, which could cause battery discharge.

The third benefit is improved idle stability. In response to the PCMs GENRC signal, the regulator uses a generator load input (GENLI) signal to provide feedback to the PCM. The GENLI signal provides the PCM with charging system information. Specifically, it lets the PCM know when the charging system receives a transient electrical load which would normally affect idle stability. Because the PCM can anticipate additional loads, actions can be taken to minimize idle sag. The PCM can choose to either reduce the regulator set point or increase engine idle speed, both of which are calibratable features. In order to establish whether the regulator is accurately maintaining the desired voltage set point, the regulator uses a charging system voltage line to sense battery voltage.

The fourth benefit is reduced cranking efforts. The PCM can reduce the mechanical load on the starter by initially commanding a low voltage set point. This may improve start times.

If the PCM detects a charging system error, it broadcasts a low voltage telltale (ON) network communication message which tells the cluster to illuminate the charge indicator. The charge indicator is illuminated if the PCM does not see a signal on the GENLI circuit for a time period greater than 500 milliseconds. This telltale command is also used to indicate over-voltage conditions detected by the PCM-controlled generator.

Each time the ignition switch is cycled to the run position, the instrument cluster initiates a bulb check by illuminating the charge indicator. It is the PCMs responsibility to issue a low voltage telltale (OFF) command if the charging system is functioning correctly. This message should be sent during the network initialization in the voluntary phase (250 milliseconds to 450 milliseconds after the ignition switch is cycled to the run position). If a low voltage telltale (OFF) communications network message is not received, the instrument cluster continues to illuminate the charge indicator indefinitely.

Scheme 6

The secondary AIR system controls emissions during the first few seconds of engine operation by forcing air downstream into the exhaust manifolds to oxidize the hydrocarbons and carbon monoxide created by running rich at start up.

The torque based ETC is a hardware and software strategy that delivers an engine output torque (via throttle angle) based on driver demand (pedal position). It uses an electronic throttle body, the powertrain control module (PCM), and an accelerator pedal assembly to control the throttle opening and engine torque. The ETC system replaces the standard cable operated accelerator pedal, idle air control (IAC) valve, 3-wire throttle position sensor (TPS), and mechanical throttle body.

Torque based ETC enables aggressive automatic transmission shift schedules (earlier upshifts and later downshifts). This is possible by adjusting the throttle angle to achieve the same wheel torque during shifts, and by calculating this desired torque, the system prevents engine lugging (low RPM and low manifold vacuum) while still delivering the performance and torque requested by the driver. It also enables many fuel economy/emission improvement technologies such as variable camshaft timing (VCT) (deliver same torque during transitions).

Torque based ETC also results in less intrusive vehicle and engine speed limiting, along with smoother traction control.

Other benefits of ETC are

1. eliminate cruise control actuators
2. eliminate idle air control (IAC) valve
3. better airflow range
4. packaging (no cable)
5. more responsive powertrain at altitude and improved shift quality

It should be noted that the ETC system illuminates a powertrain malfunction indicator (wrench) on the instrument cluster when a concern is present. Concerns are accompanied by diagnostic trouble codes (DTCs) and may also illuminate the malfunction indicator lamp (MIL).

The VCT enables rotation of the camshaft(s) relative to the crankshaft rotation as a function of engine operating conditions. There are 4 types of VCT systems.

1. Exhaust phase shifting (EPS) system - the exhaust cam is the active cam being retarded.
2. Intake phase shifting (IPS) system - the intake cam is the active cam being advanced.
3. Dual equal phase shifting (DEPS) system - both intake and exhaust cams are phase shifted and equally advanced or retarded.
4. Dual independent phase shifting (DIPS) system - where both the intake and exhaust cams are shifted independently.

All systems have 4 operational modes: idle, part throttle, wide open throttle (WOT), and default mode. At idle and low engine speeds with closed throttle, the powertrain control module (PCM) determines the phase angle based on air flow, engine oil temperature and engine coolant temperature. At part and wide open throttle the PCM determines the phase angle based on engine RPM, load, and throttle position. VCT systems provide reduced emissions and enhanced engine power, fuel economy and idle quality. IPS systems also have the added benefit of improved torque. In addition, some VCT system applications can eliminate the need for an external exhaust gas recirculation (EGR) system. The elimination of the EGR system is accomplished by controlling the overlap time between the intake valve opening and exhaust valve closing. Currently, both the IPS and DEPS systems are used

OBD-I and OBD-II Overview

The California Air Resources Board (CARB) began regulating OBD systems for vehicles sold in California beginning with the 1988 model year. The initial requirements, known as OBD-I, required identifying the likely area of concern with regard to the fuel metering system, exhaust gas recirculation (EGR) system, emission-related components and the powertrain control module (PCM). A malfunction indicator lamp (MIL) was required to illuminate and alert the driver of the concern and the need to repair the emission control system. A diagnostic trouble code (DTC) was required to assist in identifying the system or component associated with the concern.

Starting with the 1994 model year, both CARB and the Environmental Protection Agency (EPA) mandated enhanced OBD systems, commonly known as OBD-II. The objectives of the OBD-II system are to improve air quality by reducing high in-use emissions caused by emission-related concerns, reducing the time between the occurrence of a concern and its detection and repair, and assisting in the diagnosis and repair of emission-related problems.

North American OBD-II/Federal OBD requirements apply to

1. Gasoline engine passenger cars and trucks: All California and Green State (Maine, Massachusetts, New York, Vermont) passenger cars, medium duty passenger vehicles (MDPVs), and trucks up to 6,350 kg (14,000 lb) gross vehicle weight rating (GVWR). Federal trucks from 3,856 to 6,350 kg (8,500 to 14,000 lb) GVWR complete the phasing in of OBD-II. Federal heavy-duty trucks up to 4,536 kg (10,000 lb) GVWR choosing to certify using light duty truck provisions must comply with OBD-II requirements. Federal heavy-duty trucks over 6,350 kg (14,000 lb) GVWR that do not comply with OBD-II regulations must comply with OBD-I in order to meet the minimum Ford requirements. Passenger cars and trucks sold in Canada and Mexico have Federal calibrations, unless unique calibrations are certified for Mexico at high altitude. Mexico requires OBD-II for vehicles under 3,856 kg (8,500 lb) GVWR. Trucks over 3,856 kg (8,500 lb) GVWR must comply with OBD-I in order to meet the minimum Ford requirements.
2. Diesel engine passenger cars and trucks: All California and Green State passenger cars, MDPVs, and trucks up to 6,350 kg (14,000 lb) GVWR. Federal trucks from 3,856 to 6,350 kg (8,500 to 14,000 lb) GVWR complete the phasing in of OBD-II. Federal heavy-duty trucks over 6,350 kg (14,000 lb) GVWR that do not comply with OBD-II regulations must comply with OBD-I in order to meet the minimum Ford requirements.

The OBD-II system monitors virtually all emission control systems and components that can affect tailpipe or evaporative emissions. In most cases, concerns must be detected before emissions exceed 1.5 times the applicable 100,000, 120,000, or 150,000 (passenger cars), or 120,000 (trucks) mile emission standards. Partial zero emission vehicle (PZEV) and super ultra low emission vehicle (SULEV-II) vehicles can use the concern criteria of 2.5 in lieu of the 1.5 standard whenever required. Federal Tier 2 (Bin 3 and 4) must use a 1.5 concern criteria for non-methane organic gases (NMOG) and carbon monoxide (CO), a 1.75 criteria for NMOG catalyst monitor, and a 2.5 criteria for oxides of nitrogen (NO x ). If a system or component exceeds emission thresholds or does not operate within a manufacturer's specifications, a DTC is stored and the MIL is illuminated within 2 driving cycles.

The OBD-II system monitors for concerns either continuously, regardless of driving mode, or non-continuously, once per drive cycle during specific drive modes. A pending DTC is stored in the PCM keep alive memory (KAM) when a concern is initially detected. Pending DTCs are displayed as long as the concern is present. Note that OBD regulations required a complete concern-free monitoring cycle to occur before erasing a pending DTC. This means that a pending DTC is erased on the next power-up after a concern-free monitoring cycle. However, if the concern is still present after 2 consecutive drive cycles, the MIL is illuminated. Once the MIL is illuminated, 3 consecutive drive cycles without a concern detected are required to extinguish the MIL. The DTC is erased after 40 engine warm-up cycles once the MIL is extinguished.

In addition to specifying and standardizing much of the diagnostics and MIL operation, OBD requires the use of a standard data link connector (DLC), standard communication links and messages, standardized DTCs and terminology. Examples of standard diagnostic information are freeze frame data and inspection maintenance (IM) readiness indicators.

Freeze frame data describes data stored in the KAM at the point the concern is initially detected. Freeze frame data consists of parameters such as engine RPM and load, state of fuel control, spark, and warm-up status. Freeze frame data is stored at the time the first concern is detected; however, previously stored conditions are replaced if a fuel or misfire concern is detected. This data is accessible with the diagnostic tool to assist in repairing the vehicle.

OBD IM readiness indicators show whether all of the OBD monitors have been completed since the last time the KAM or the PCM DTC(s) have been cleared. Ford also stores a P1000 DTC to indicate that some monitors have not completed. In some states, it may be necessary to carry out an OBD check in order to renew a vehicle registration. The IM readiness indicators must show that all monitors have been completed prior to the OBD check.

Vehicles not required to comply with OBD-II requirements use an OBD-I system. OBD-I systems are used on all Federal truck calibrations over 3,856 kg (8,500 lb) GVWR. OBD-I vehicles use the same data communication link, DLC, and PCM software as the corresponding OBD-II vehicle. Differences between OBD-I and OBD-II vehicles may be removal of the rear oxygen sensor(s), fuel tank pressure sensor, canister vent solenoid, and PCM calibration. The table below lists what monitors and functions have been altered for the OBD-I calibration.

MONITOR/FEATURE AND CALIBRATION REFERENCE CHART

The following monitor descriptions provide a general description of each OBD monitor. In these descriptions, the monitor strategy, hardware, testing requirements, and methods are presented to provide an overall understanding of monitor operation. An illustration of each monitor may also be provided. These illustrations should be used as typical examples and are not intended to represent all possible vehicle configurations.

Each illustration depicts the PCM as the main focus with primary inputs and outputs for each monitor. The icons to the left of the PCM represent the inputs used by each of the monitor strategies to enable or activate the monitor. The components and subsystems to the right of the PCM represent the hardware and signals used while carrying out the tests and the systems being tested. The comprehensive component monitor (CCM) illustration has numerous components and signals involved which are shown generically. When referring to the illustrations, match the numbers to the corresponding numbers in the monitor descriptions for a better comprehension of the monitor and associated DTCs.

These icons are used in the illustrations of the OBD monitors and throughout this article.

Scheme 7

General Catalyst Monitor Operation

Monitor execution is once per drive cycle. The typical monitor duration is 700 seconds. In order for the catalyst monitor to run, the HO2S monitor must be complete and the secondary AIR and EVAP system functional with no stored DTCs. If the catalyst monitor does not complete during a particular driving cycle, the already accumulated switch/signal data is retained in the KAM and is used during the next driving cycle to allow the catalyst monitor a better opportunity to complete.

Rear HO2S can be located in various configurations to monitor different kinds of exhaust systems. In-line engines and many V-engines are monitored by their individual bank. A rear HO2S is used along with the front, fuel control HO2S for each bank. Two sensors are used on an in-line engine and 4 sensors are used on a V-engine. Some V-engines have exhaust banks that combine into a single underbody catalyst. These systems are referred to as Y-pipe systems. They use only 1 rear HO2S along with the 2 front, fuel-control HO2S. The Y-pipe system uses 3 sensors in all. For Y-piped systems, the 2 front HO2S signals are combined by the PCM software to infer what the HO2S signal would have been in front of the monitored catalyst. The inferred front HO2S signal and the actual single, rear HO2S signal is then used to calculate the index ratio.

Exhaust systems that use an underbody catalyst without a downstream/rear HO2S are not monitored by the catalyst efficiency monitor.

Most vehicles that are part of the low emission vehicle (LEV) catalyst monitor phase-in, monitor less than 100% of the catalyst volume. Often this is the first catalyst brick of the catalyst system. Partial volume monitoring is done on LEV and ultra low emission vehicle (ULEV) vehicles in order to meet the 1.75 emission standard. The rationale for this strategy is that the catalyst nearest the engine deteriorate first, allowing the catalyst monitor to be more sensitive and illuminate the MIL correctly at lower emission standards.

Many applications that use partial-volume monitoring place the rear HO2S after the first light-off catalyst can or after the second catalyst can in a 3-can per bank system. (A few applications placed the HO2S in the middle of the catalyst can, between the first and second bricks).

Some partial zero emission vehicles (PZEV) use 3 sets of HO2S per engine bank. The front sensors or stream 1 (HO2S11/HO2S21) are the primary fuel control sensors. The next sensors downstream or stream 2 in the exhaust are used to monitor the light-off catalyst (HO2S12/HO2S22). The last sensors downstream or stream 3 in the exhaust (HO2S13/HO2S23) are used for very long term fuel trim in order to optimize catalyst efficiency (fore aft oxygen sensor control). For additional heated oxygen sensor information, refer to the HEATED OXYGEN SENSOR (HO2S) MONITOR .

Index ratios for ethanol (flex fuel) vehicles vary based on the changing concentration of alcohol in the fuel. The threshold to determine a concern typically increases as the percent of alcohol increases. For example, a threshold of 0.5 may be used at E10 (10% ethanol) and 0.9 may be used at E85 (85% ethanol). The thresholds are therefore adjusted based on the percentage of alcohol in the fuel. Standard fuel may contain up to 10% ethanol.

Scheme 8

The cold start emission reduction monitor is being introduced to meet the low emissions vehicle-II (LEV-II) emissions standards. The monitor works by validating the operation of the components of the system required to achieve the cold start emission reduction strategy, retarded spark timing and elevated idle airflow.

Cold start emission reduction low airflow test operation

1. DTC: P050A cold start idle air control system performance
2. Monitor execution: Once per driving cycle, from start up with the cold start emissions reduction active
3. Monitor sequence: none
4. Monitoring duration: 7 seconds

Misfire Monitor Operation

There are 3 different misfire monitoring technologies used. They are low data rate (LDR) and high data rate (HDR), and neural network misfire (NNM). The LDR system is capable of meeting the federal test procedure monitoring requirements on most engines and is capable of meeting the full-range of misfire monitoring requirements on 4-cylinder engines. The HDR system is capable of meeting the full-range of misfire monitoring requirements on 6 and 8 cylinder engines. The NNM detection system is being introduced to improved detection ranges and cylinder identification for a wider range of misfire patterns on some 8, 10, and 12 cylinder vehicles with neural network detection are full range capable. HDR is being phased in on these engines to meet the full-range of misfire phase-in requirements specified in the OBD regulations. All engines except the 6.8L V-10 are full-range capable. All 2006 MY software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the new OBD requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle RPM.