Engine Controls - Theory & Operation - Cng, Flex-Fuel & Gasoline: Overview Ford Econoline E150

OBD-I and OBD-II Overview

The California Air Resources Board (CARB) began regulating On Board Diagnostic (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 malfunction 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) labeled CHECK ENGINE or SERVICE ENGINE SOON was required to illuminate and alert the driver of the malfunction and the need to service the emission control system. A fault code or Diagnostic Trouble Code (DTC) was required to assist in identifying the system or component associated with the fault.

Starting with the 1994 model year, both CARB and 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 malfunctions, reducing the time between the occurrence of a malfunction 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 engines: All California (CA), Massachusetts (MA), and New York (NY) Federal passenger cars, California, MA, and NY Medium Duty Passenger Vehicles (MDPVs) and trucks up to 14,000 lbs. GVWR (Gross Vehicle Weight Rating). Federal trucks from 8,500 lbs. to 14,000 GVWR will begin phasing in OBD-II starting in the 2004 model year. Federal heavy-duty trucks up to 10,000 lbs. GVWR choosing to certify using Light Duty Truck provisions must comply with OBD-II requirements. Federal heavy-duty trucks over 8,500 lbs. GVWR that do not comply with OBD -II regulations must comply with OBD-I in order to meet minimum Ford serviceability requirements. Passenger cars and trucks sold in Canada and Mexico have Federal calibrations, unless unique calibrations are certified for Mexico at high altitude.
2. Diesel Engines: All passenger cars and California trucks up to 14,000 lb. GVWR. Federal trucks from 8,500 lbs. to 14,000 lbs.GVWR will begin phase in of OBD II starting in the 2004MY.
3. Alternative fuel vehicles (AFV): Ethanol/methanol AFVs must meet full OBD-II requirements during operation on all fuels. Bi-fuel NGVs/LPGs are required to meet full OBD-II requirements while operating on gasoline. Dedicated NGVs and bi-fuel NGVs/LPGs are required to partially meet OBD-II requirements while operating on gaseous fuels.

"Green States" are states that choose to adopt California emission regulations. National Low Emission Vehicle (NLEV) is a vehicle required to compliance with California OBD-II, including the 0.020" evaporative system monitoring requirements. Both the NLEV and "Green States" receive California vehicles for all passenger cars and trucks < 6,000 lbs. GVWR. "Green States" are: MA, NY, VT and ME. NLEV states are: VA, CT, RI, MD, NJ, PA, DE and Washington DC.

The OBD-II system monitors virtually all emission control systems and components that can affect tailpipe or evaporative emissions. In most cases, malfunctions must be detected before emissions exceed 1.5 times the applicable 100K, 120K or 150K passenger cars or 120K trucks - mile emission standards. Partial Zero Emission Vehicle (PZEV), Super Ultra Low Emission Vehicle (SULEV-II) and Federal Tier 2 (Bin 3 and 4) vehicles can use malfunction criteria of 2.5 in lieu of 1.5 standard whenever required. If a system or component exceeds emission thresholds or fails to operate within a manufacturer's specifications, a DTC will be stored and the MIL will be illuminated within two driving cycles.

The OBD-II system monitors for malfunctions 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 malfunction is initially detected. This pending DTC may be erased on the third vehicle restart after two consecutive drives cycles with no malfunction. However if the malfunction is still present after two consecutive drive cycles, the MIL is illuminated. Once the MIL is illuminated, three consecutive drive cycles without a malfunction 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-II requires the use of a standard Diagnostic Link Connector (DLC), standard communication links and messages, standardized DTC and terminology. Examples of standard diagnostic information are freeze frame data and Inspection Maintenance (IM) Readiness Indicators.

Freeze frame data describes data stored in KAM at the point the malfunction 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 malfunction is detected, however, previously stored conditions will be replaced if a fuel or misfire fault is detected. This data is accessible with the scan tool to assist in repairing the vehicle.

OBD Inspection Maintenance (IM) Readiness indicators show whether all of the OBD monitors have been completed since the last time 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 perform 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 will utilizes an OBD-I system. OBD-I systems are used on all Federal truck calibrations over 8,500 lbs. GVWR. OBD-I vehicles use the same data communication link, data link connector (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.

MONITORS AND FUNCTIONS

The following information provides a general description of each On Board Diagnostic 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 is also 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 performing the tests and the systems being tested. The Comprehensive Component Monitor (CCM) illustration has numerous components and signals involved and 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 DTC's.

These icons are used in the illustrations of the On Board Diagnostic monitors and throughout this article.

Scheme 169

General Catalyst Monitor Operation

Monitor execution is once per drive cycle. Typical monitor duration is 700 seconds. In order for the catalyst monitor to run, the HO2S monitor must be complete and 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 Keep Alive Memory and is used during the next driving cycle to allow the catalyst monitor a better opportunity to complete.

Rear HOS2 sensors 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 sensor is used along with the front, fuel control HO2S sensor for each bank. Two sensors are used on an in-line engine; four 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 one rear HO2S sensor along with the two front, fuel-control HO2S sensors. Y-pipe system uses three sensors in all. For Y-piped systems, the two front HO2S sensor 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 switch ratio.

Most vehicles that are part of the Low Emission Vehicle (LEV) catalyst monitor phase-in will 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.

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

Some Partial Zero Emission Vehicles (PZEV) will utilize three sets of HO2S sensors 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 utilized to monitor the light-off catalyst (HO2S12/HO2S22). The last sensors downstream or stream 3 in the exhaust (HO2S13/HO2S23) are utilized for very long term fuel trim in order to optimize catalyst efficiency (For Aft Oxygen Sensor Control). For addition heated oxygen sensor information, refer to the HEATED OXYGEN SENSOR (HO2S) MONITOR .

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

Scheme 170

Misfire Monitor Operation

There are two different misfire monitoring technologies used in the 2004 MY. They are Low Data Rate (LDR) and High Data Rate (HDR). The LDR system is capable of meeting the FTP monitoring requirements on most engines and is capable of meeting full-range misfire monitoring requirements on 4 -cylinder engines. The HDR system is capable of meeting full-range misfire monitoring requirements on 6 and 8 cylinder engines. HDR is being phased in on these engines to meet the full-range misfire phase-in requirements specified in the OBD-II regulations. All engines except the 6.8L V-10 are full-range capable. All 2004 MY software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the new OBD-II requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle rpm.

Overview

The 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 onboard diagnostics (OBD) monitoring system 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 powertrain control module (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 in this article.

This article contains 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 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).

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 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 proper vehicle operation and misfire detection.

The fuel system supplies the sequential multi-port 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. If the injectors have been replaced 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 three types of fuel systems used are

1. Returnable Fuel
2. Mechanical Returnless Fuel
3. Electronic Returnless Fuel

The Fuel System provides a means of transporting clean fuel from the fuel tank to the fuel injectors under a controlled pressure.

Fuel Rail Valve Circuit Operation

When the key is turned to the ON position, the power relay is turned on. The power relay provides power to the PCM and the control side of the fuel shut off valve relay. The relay provides voltage to the fuel rail valve. If the ignition switch is not turned to the START position, the PCM will shut off the fuel rail valve after one second. The PCM will open the valve (along with the four tank valves) to provide fuel while cranking. The valve will remain open when the engine is running unless the inertia fuel shut-off switch is "tripped."

Scheme 171

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 EEGR system uses exhaust gas recirculation to control the oxides of nitrogen (NOx) 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 PCM, and connecting wiring. Additionally a MAP sensor is also required. Operation of the system is as follows (Scheme 172)

1. 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 manifold absolute pressure (MAP) sensor 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 will deactivate EEGR during idle, extended wide open throttle or whenever a failure 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 will output signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor will directly actuate 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 TMAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into the intake manifold. Variations in EGR being used will correlate to the TMAP signal (increasing EGR will increase manifold pressure values).

Scheme 172

The ESM EGR system is an updated DPFE EGR 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 EGR System Module (ESM) (Scheme 173) 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 PCM with a differential DPFE signal, identical to a traditional DPFE system.

Scheme 173

The Delta Pressure Feedback EGR Monitor is comprised of a series of electrical tests and functional tests that monitor various aspects of EGR system operation.

First, the Delta Pressure Feedback EGR (DPFE) sensor input circuit is checked for out of range values (P1400/P0405 P1401/P0406). The Electronic Vacuum Regulator (EVR) output circuit is checked for opens and shorts (P1409/P0403).

Note. EGR 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 MIL illumination for temporary freezing, the following logic is used

If an EGR system malfunction is detected below 32°F, only the EGR system is disabled for the current driving cycle. A DTC is not stored and the I/M readiness status for the EGR monitor will not change. The EGR monitor will, however, continue to operate. If the EGR monitor determines that the malfunction is no longer present (i.e., the ice melts), the EGR system will be enabled and normal system operation will be restored.

If an EGR system malfunction is detected above 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 malfunction has been detected on two consecutive driving cycles.

After the vehicle is started, during initial vehicle acceleration, the differential pressure indicated by the DPFE sensor at zero EGR flow is checked to ensure that both hoses to the DPFE sensor are connected. Under this condition, the differential pressure should be zero. If the differential pressure indicated by the DPFE sensor exceeds a maximum threshold or falls below a minimum threshold, an upstream or downstream DPFE hose malfunction is indicated (P1405 P1406).

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check is performed. Since the EGR system is a closed loop system, the EGR system will deliver 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 calibratable threshold, a low flow malfunction in indicated (P0401/P0406).

Finally, the differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR flow to perform the high flow check. If the differential pressure exceeds a calibratable 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 32°F, or greater than 140°F, or the altitude is greater than 8,000 feet (BARO < 22.5 "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 decrementing, and, if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds, the EGR monitor is disabled for the remainder of the current driving cycle and the EGR Monitor I/M Readiness bit will be set to a "ready" condition after one such driving cycle. Vehicles will require two such driving cycles for the EGR Monitor to be set to a "ready" condition.

Scheme 174

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

All applications required to meet OBD-II regulations, utilize the Enhanced Evaporative Emission (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 Intake Air system (Scheme 175) 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. The main component of the intake air system is the air cleaner assembly. The air cleaner assembly houses the air cleaner element that removes potential engine contaminants, particularly abrasive types. The mass air flow (MAF) sensor is attached internally or externally to the air cleaner assembly and measures the quantity of air delivered to the engine combustion chamber. The MAF sensor can be serviced or replaced as an individual component. The intake air system also contains a sensor that measures the intake air temperature which may also be integrated with the MAF sensor. (Refer to Electronic EC Hardware - PCM INPUTS for additional information on the MAF and IAT sensors.) Air induction resonators can be separate components or part of the intake air housing (i.e., conical air cleaner). 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 175

Note. For additional illustrations, refer to the appropriate service information article.

There are three basic types of intake air sub-systems

1. Intake Manifold Runner Control (IMRC) electric actuated system
2. Intake Manifold Swirl Control (IMSC) vacuum actuated system
3. Intake Manifold Tuning Valve (IMTV)

These subsystems are used to provide increased intake airflow to improve torque, emissions and performance. The overall quantity of air metered to the engine is controlled by the throttle body.

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) .

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, 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 PCV valve. The IAC valve assembly provides additional air when commanded by the powertrain control module (PCM) to maintain the proper engine idle speed under varying conditions. The IAC valve assembly mounts directly to the throttle body assembly in most applications, but is remote-mounted to the intake manifold in some applications. Idle speed is controlled by the PCM and cannot be adjusted.

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

Throttle rotation is controlled by a cam/cable linkage to slow the initial opening rate of the throttle plate. The TP sensor monitors throttle position and provides an electrical signal to the PCM. Some throttle body applications provide an air supply channel upstream of the throttle plate to provide fresh air to the Positive Crankcase Ventilation (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.

The Secondary Air Injection (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.

Variable Cam Timing (VCT) enables rotation of the camshaft(s) relative to the crankshaft (phase-shafting) as a function of engine operating conditions. There are four 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 four operational modes; idle, part throttle, wide open throttle and default mode. At idle and low engine speeds with closed throttle, the phase angle are controlled by air flow, engine oil temperature and engine coolant temperature. At part and wide open throttle the PCM controls cam timing 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 improve torque. In addition, on some applications a VCT system can eliminated the need for an external Exhaust Gas Recirculation (EGR) system. The elimination of the EGR system is accomplished by controlling the overlap in valve opening between the intake valve opening and exhaust valve closing.

Currently for the 2004 model year, Ford Motor Company uses the IPS and DEPS systems. The IPS system is on Lincoln LS, Thunderbird and Focus SVT and the DEPS system is on the F150 5.4L 3V.

The Positive Crankcase Ventilation (PCV) System (Scheme 176) 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 and prevents backfire from traveling into the crankcase.

Currently, Ford uses heated and non-heated PCV valves. The purpose of the PCV heater is to prevent the PCV valve from freezing in cold ambient temperatures. Heated PCV valves are heated either by water or electric. Water heated systems use engine coolant to heat the valve to prevent freezing. Electrically heated systems use a heating element enclosed in the PCV valve to prevent the valve from freezing. Ford currently uses two types of electrically heated PCV valve systems

1. Thermal harness controlled - On vehicle application that are equipped with a thermal harness to the PCV valve. The thermal harness only provides electrical continuity to the heating element when temperature are less than 40°F (5°C +/-7°F (+/-4°C). Typically this harness is located close to the PCV valve.
2. PCM heater controlled - On these applications the PCV heater is turned on by the PCM. When the intake air temperature is less than 32°F (0°C) the PCM grounds the Positive Crankcase Ventilation Valve Heater Control (PCVHC) circuit and turns the heater ON. When the intake air temperature exceeds 48°F (9°C) 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 above 16 volts. This minimizes heater element overload.

Refer to the following figures for examples of these types of PCV valves.

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

Scheme 176

Scheme 177

Scheme 178

Scheme 179

Scheme 180

Note. On vehicle applications that are equipped with a thermal harness to the PCV valve. The thermal harness only provides electrical continuity when temperatures is less than 40° F (5° C) +/- 7° F (+/ - 4°C).

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). CO, NO x , and HCs are major air pollutants, 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 will be used between the front and rear exhaust pipes. Catalytic converter efficiency is monitored by the On Board Diagnostic (OBD) system strategy in the PCM. Refer to the CATALYST EFFICIENCY MONITOR -Federal Test Procedure for specific OBD catalyst monitor information.

The number of HO2S(s) used in the exhaust stream and the location of these sensors depend on the vehicle emission certification level (i.e. LEV, ULEV, PZEV). Refer to (Scheme 181) and (Scheme 182) for typical HO2S stream locations and naming convention. On most vehicles only two HO2S are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control while the ones after the catalyst (HO2S12/HO2S22) will be utilized to monitor catalyst efficiency. However, some Partial Zero Emission Vehicles (PZEV) will utilize three HO2S sensors for each engine bank. The stream 1 sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control, the next group of sensors or stream 2 (HO2S12/HO2S22) is utilized to monitor the light-off catalyst and the last group of sensors or stream 3 (HO2S13/HO2S23) is utilized for long term fuel trim control to optimize catalyst efficiency (Fore Aft Oxygen Sensor Control). Currently Ford's PZEV vehicles use only a 4-cylinder engine, so only the Bank 1 HO2S(s) will be utilized.

Scheme 181

Scheme 182

The PCM-Controlled charging system (Scheme 183) 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. Field data has shown this approach lacks accuracy. With a PCM-controlled generator, the regulator voltage set point is determined by the PCM and communicated to the regulator via the generator communication line. The PCM will use a calibratable algorithm to estimate battery temperature. Improving battery temperature estimates will reduce 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 will momentarily lower 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 PCM's generator communication signal, the regulator uses a generator monitor signal to provide feedback to the PCM. The generator monitor 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 at the rear power distribution box.

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 will broadcast a low voltage telltale (ON) command which tells the cluster to light the charge indicator. The charge indicator will be illuminated if the PCM fails to see a signal on the generator monitor line for a time period greater than 500 milliseconds. This telltale command will also be used to indicate over-voltage conditions detected by the PCM controlled generator.

Each time the ignition switch is cycled to the run position, the cluster will initiate a bulb check by illuminating the charge indicator. It is the PCM's responsibility to issue a low voltage telltale (OFF) command if the charging system is functioning properly. This message should be sent during 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) command is not received by the cluster, the cluster will continue to light the charge light indefinitely.

Scheme 183

The Generation II (Gen II) Torque Based Electronic Throttle Control (ETC) is a hardware and software strategy that delivers a transmission output shaft torque (via throttle angle) based on driver demand (pedal position). It utilizes an electronic throttle body, the PCM and a accelerator pedal assembly to control throttle opening and engine torque. The ETC system basically replaces the standard cable operated accelerator pedal, idle air control (IAC) motor, 3-wire throttle position sensor (TPS) and mechanical throttle body.