Engine Controls - Description & Operation (Except Diesel & Hybrid) (Section 1): Overview Ford Explorer V

PTO Circuits Description

The 3 PTO input circuits are PTO mode, PTO engage, and PTO RPM.

The PTO engage circuit is used when the operator is requesting the PCM to check the needed inputs required to initiate the PTO engagement.

The PTO RPM circuit is used when the operator is requesting additional engine RPM for PTO operation.

Overview

The EC system provides optimum control of the engine and transmission through the enhanced capability of the powertrain control module (PCM). The EC 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). Even though it is still part of the EC system, the stand alone TCM communicates with the PCM, the antilock brake system (ABS) module, the instrument cluster (IC) or instrument panel cluster (IPC), and the four-wheel drive (4WD) control modules using the high speed controller area network (CAN) communications network. The stand alone TCM incorporates a stand-alone OBD II system. The stand alone TCM independently processes and stores diagnostic trouble codes (DTCs), freeze frame data, support parameter identifications (PIDs) as well as J1979 Mode 09 CALID and calibration verification number. The stand alone TCM does not directly illuminate the malfunction indicator lamp (MIL), but requests the PCM to do so. The stand alone TCM is located inside the transmission assembly. It is not repairable, with the exception of reprogramming.

For additional information on TCM diagnostics, refer to the appropriate Automatic Transaxle/Transmission article.

The EC 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 EC hardware and software are discussed in this service information.

This information contains detailed descriptions of the operation of the EC 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 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).

International Standards Organization (ISO) 14229 Diagnostic Trouble Code (DTC) Descriptions

The ISO 14229 is a global, diagnostic communication standard. The 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. The ISO 14229 is similar to the Society of Automotive Engineers (SAE) J2190 diagnostic communication standard that was used by all Original Equipment Manufacturers (OEMs) for previous communication protocols, like J1850 standard corporate protocol (SCP).

The 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.

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 (H 2 O). However, it also contains carbon monoxide (CO), nitrogen oxides (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 powertrain control module (PCM). For additional information on the OBD catalyst monitor, refer to the description for the CATALYST EFFICIENCY MONITOR .

Only two HO2Ss are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst are used for primary fuel control while the sensors after the catalyst (HO2S12/HO2S22) are used to monitor catalyst efficiency.

Scheme 1

Scheme 2

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 on the description and operation of the evaporative emission system.

The EGR system controls the nitrogen oxides (NO x ) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air to fuel charge. The combustion chamber temperature is reduced, lowering NO x emissions.

The EEGR system uses exhaust gas recirculation to control the 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 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 3

1. The EEGR system receives signals from the ECT or CHT sensor, TP sensor, MAF sensor, 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 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 to control 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 a fully open position. The position of the EGR valve determines the EGR flow.
4. A MAP sensor measures 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 functions in the same manner as a conventional differential pressure feedback EGR 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. 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 MAP. This MAP signal is used for EGR correction and inferred barometric pressure (BARO) at ignition ON. The system provides the PCM with a differential pressure feedback EGR signal.

First, the differential pressure feedback EGR sensor input circuit is checked for out of range values (DTC P0405 or P0406). The EGR vacuum regulator output circuit is checked for opens and shorts (DTC 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 differential pressure feedback EGR sensor, hoses, as well as other components in the EGR system. 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 inspection/maintenance (I/M) readiness status for the EGR monitor does not change. The EGR monitor, however, continues to operate. If the EGR monitor determines 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 are disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the concern has been detected for 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 EGR vacuum regulator duty cycle is at maximum (90% duty cycle), the differential pressure indicated by the differential pressure feedback EGR 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 (DTC P0401 or P0406).

Finally, the differential pressure indicated by the differential pressure feedback EGR 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 (DTC 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. 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 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 high pressure fuel system receives low pressure fuel from the fuel pump assembly and delivers fuel at high pressure to the direct injection fuel injectors.

The high pressure fuel system consists of the fuel injection pump, the fuel volume regulator, the fuel rail pressure (FRP) sensor, the fuel supply line, the fuel rail, and the fuel injectors. For additional information on the fuel system components, refer to ENGINE CONTROL COMPONENTS . Operation of the system is as follows

Scheme 4

1. The fuel injection pump receives fuel from the fuel pump assembly, increases the fuel pressure from approximately 448 kPa (65 psi) to a powertrain control module (PCM) determined pressure up to as high as 15 MPa (2175 psi), and delivers it to the fuel rails.
2. The fuel volume regulator controls the volume of low pressure fuel that enters the inlet check valve and the pump piston inside the fuel injection pump. The PCM regulates fuel pressure by controlling the timing of the fuel volume regulator solenoid.
3. High pressure fuel exits the fuel injection pump and is delivered to the fuel rails through the fuel supply line.
4. The fuel rails distribute and channel high pressure fuel to the fuel injectors.
5. The FRP sensor provides a feedback signal to indicate the fuel rail pressure so the PCM can command the correct injector timing and pulse width for correct fuel delivery at all speed and load conditions.
6. The fuel injectors meter fuel flow to the engine. A given cylinder fuel injector can deliver single or multiple injections for each cylinder event. The amount of fuel is controlled by the length of time the fuel injectors are held open.

The ignition system is designed to ignite the compressed air to fuel mixture in an internal combustion engine by a high voltage spark delivered from an ignition coil controlled by the powertrain control module (PCM).

The intake air system provides clean air to the engine, optimizes airflow, 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 intake air system. The mass airflow (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 evaporative emission (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 integrated with the MAF sensor. For additional information on the intake air system components, refer to ENGINE CONTROL COMPONENTS . Intake air components can be separate components or part of the intake air housing. The function of a resonator is to reduce induction noise. The intake air components are connected to each other and to the throttle body assembly with hoses.

Scheme 5

Throttle Body System Overview

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 single or dual bores with butterfly valve throttle plates and a throttle position (TP) sensor. The airflow is measured by the MAF sensor.

The major components of the throttle body assembly include the TP sensor and the throttle body housing assembly. For additional information on the intake air system components, refer to ENGINE CONTROL COMPONENTS .

Overview Of The Intake Manifold Tuning Valve (IMTV) System

The IMTV is a manifold tuning device that affects the airflow 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 system does not have to be monitored for OBD II regulations.

This subsystem provides increased intake airflow to improve torque, emissions and performance. The overall volume of air metered to the engine is controlled by the throttle body.

The IMTV is a motorized actuated unit mounted directly to the intake manifold. For additional information on IMTV components, refer to ENGINE CONTROL COMPONENTS .

The motorized IMTV unit is not energized below a calibrated RPM. The shutter is in the closed position not allowing airflow blend to occur in the intake manifold. Above a calibrated RPM the motorized unit is energized. The motorized unit is initially commanded ON by the PCM at a 100 percent duty cycle to move the shutter to the open position, and then falling to approximately 50 percent to continue to hold the shutter open.

Scheme 6

1. The PCM uses the TP sensor and CKP sensor signals to determine activation of the IMTV system. There must be a positive change in voltage from the TP sensor along with the increase in RPM to open the shutter.
2. The PCM uses the information from the input signals to control the IMTV.
3. When commanded ON by the PCM, the motorized actuator shutter opens up the end of the vertical separating wall at high engine speeds to allow both sides of the manifold to blend together.

The PCV system cycles crankcase gases back through the intake air 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, PCV fitting or the PCV tube to prevent the valve or tube from freezing. The valve or the tube heater is controlled by the powertrain control module (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 on board diagnostics (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 .

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 (ETB), the powertrain control module (PCM), and an accelerator pedal assembly to control the throttle opening and engine torque.

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), which delivers 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 torque based 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

The ETC system illuminates a powertrain malfunction indicator (wrench) on the instrument cluster (IC) or instrument panel cluster (IPC) when a concern is present. Concerns are accompanied by diagnostic trouble codes (DTCs) and may also illuminate the malfunction indicator lamp (MIL).

The VCT system 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) - the exhaust cam is the active cam being retarded.
2. Intake phase shifting (IPS) - the intake cam is the active cam being advanced.
3. Dual equal phase shifting (DEPS) - both intake and exhaust cams are phase shifted and equally advanced or retarded.
4. Twin independent phase shifting - 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 airflow, 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.

The VCT system knocking and noise concerns are diagnosed in the appropriate Service Information . For additional information, refer to the appropriate Engine System - General Information article. Verification of incorrect VCT phasing on a warm engine operating below 1500 RPM can be isolated using a stethoscope and by monitoring the PIDs using a scan tool. If the VCT phaser does not maintain correct valve timing, low oil pressure or oil flow restrictions are primary possible causes. Verify correct oil pressure and flow, refer to the appropriate Engine System - General Information article.

OBD I, OBD II And Engine Manufacturer Diagnostics (EMD) 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.

The cold start emission reduction monitor is an on-board strategy designed for vehicles that meet the low emissions vehicle-II (LEV-II) emissions standards. The monitor works by detecting the lack of catalyst warm up resulting from a failure to apply sufficient cold start emission reduction during a cold start. There are 2 types of monitors

1. cold start emission reduction component monitor
2. cold start emission reduction system monitor

Cold Start Engine Speed Monitor Operation

Once the waiting period is complete, the monitor compares the average difference between desired and commanded spark to a calibrated threshold that is a function of the engine coolant temperature at start. If the difference exceeds the calibrated threshold, a DTC sets.

1. DTC: P050A Cold start idle air control system performance
2. Monitor execution: Once per driving cycle, during the first 15 seconds of a cold start
3. Monitor sequence: None
4. Monitoring duration: Data gathering occurs during the first 15 seconds of a cold start. The decision to set P050A is made 300 seconds after start. This delay gives time for other diagnostics (for example, misfire monitor) to determine if another DTC should set instead of P050A.

Cold Start Spark Timing Monitor Operation

Once the waiting period is complete, the monitor compares the average difference between desired and commanded spark to a calibrated threshold that is a function of the engine coolant temperature at start. If the difference exceeds the calibrated threshold, a DTC is set.

1. DTC: P050B Cold start ignition timing performance
2. Monitor execution: Once per driving cycle, during the first 15 seconds of a cold start
3. Monitor sequence: None
4. Monitoring duration: Data gathering occurs during the first 15 seconds of a cold start. The decision to set P050B is made 300 seconds after start. This delay gives time for other diagnostics (for example, misfire monitor) to determine if another DTC should set instead of P050B.

Cold Start Emission Reduction System Monitor Operation

1. DTC: P050E Cold start engine exhaust temperature too low
2. Monitor execution: Once per driving cycle, during the first 15 seconds of a cold start
3. Monitor sequence: None
4. Monitoring duration: Data gathering occurs during the first 15 seconds of a cold start. The decision to set P050E is made 300 seconds after start. This delay gives time for other diagnostics (for example, misfire monitor) to determine if another DTC should set instead of P050E.

Misfire Monitor Operation

A low data rate (LDR) and high data rate (HDR) are the 2 different types of misfire monitoring systems used. 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-cylinder and 8-cylinder engines. The HDR system on these engines meets the full range of misfire phase-in requirements specified in the on board diagnostic (OBD) regulations. The PCM software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the OBD requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle RPM.