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ENGINE CONTROL COMPONENTSNote: Transmission inputs which are not described are discussed in the applicable transmission system.
Accelerator Pedal Position (APP) Sensor
The APP sensor is an input to the powertrain control module (PCM) and determines the amount of torque requested by the operator. Depending on the application, either a 2 track or 3 track APP sensor is used.
2 Track APP Sensor - Fiesta
There are 2 separate pedal position sensors in the accelerator pedal. The APP1 sensor signal generates a pulse width modulated (PWM) signal to the PCM. The APP1 sensor uses a VPWR circuit, a ground circuit and a signal circuit. Only the APP1 signal circuit is connected to the PCM. The APP2 sensor signal has a positive slope (increasing angle, increasing voltage) and is a class 2 message from the instrument panel cluster (IPC) to the PCM. The APP2 sensor uses a reference voltage circuit, a signal return circuit, and a signal circuit between the IPC and the APP sensor assembly. The two pedal position signals make sure the PCM receives a correct input even if one of the signals has a concern. The PCM determines if a signal is incorrect by calculating an expected position, inferred from the other signals. If a concern is present with one of the circuits the other input is used. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. For additional information, refer to Torque Based Electronic Throttle Control (ETC).
2 Track APP Sensor - All Others
There are 2 pedal position signals in the sensor. Both signals, APP1 and APP2, have a positive slope (increasing angle, increasing voltage), but are offset and increase at different rates. The 2 pedal position signals make sure the PCM receives a correct input even if one of the signals has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other input is used. There are 2 reference voltage circuits, 2 signal return circuits, and 2 signal circuits (a total of 6 circuits and pins) between the PCM and the APP sensor assembly. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. For additional information, refer to Torque Based Electronic Throttle Control (ETC).
3 Track APP Sensor
There are 3 pedal position signals in the sensor. Signal 1, APP1, has a negative slope (increasing angle, decreasing voltage) and signals 2 and 3, APP2 and APP3, both have a positive slope (increasing angle, increasing voltage). During normal operation, APP is used as the indication of pedal position by the strategy. The 3 pedal position signals make sure the PCM receives a correct input even if one signal has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other inputs are used. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. There are 2 reference voltage circuits, 2 signal return circuits, and 3 signal circuits (a total of 7 circuits and pins) between the PCM and the APP sensor assembly.
Ambient Air Temperature (AAT) Sensor
The AAT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The AAT sensor provides ambient air temperature information to the PCM for the temperature sensor correlation tests. The PCM also communicates the AAT sensor information to all other modules on the controller area network (CAN).
Barometric Pressure (BARO) Sensor
The BARO sensor directly measures barometric pressure to estimate the exhaust back pressure. Exhaust back pressure influences speed density based air charge computation. The BARO sensor is mounted directly to the PCM circuit board.
Brake Pedal Position (BPP) Switch
The BPP switch is sometimes referred to as the stoplamp switch. The BPP switch provides a signal to the PCM indicating the brakes are applied. The BPP switch is normally open and mounted on the brake pedal support. Depending on the vehicle application the BPP switch can be hardwired as follows:
- to the PCM supplying battery positive (B+) voltage when the brake pedal is applied.
- to the anti-lock brake system (ABS) module, or lighting control module (LCM), the BPP signal is then broadcast over the network to be received by the PCM.
- to the ABS traction control/stability assist module. The ABS module interprets the BPP switch input along with other ABS inputs and generates an output called the driver brake application (DBA) signal. The DBA signal is then sent to the PCM and to other BPP signal users.
Brake Pressure Switch
The brake pressure switch is used for vehicle speed control deactivation. A normally closed switch supplies battery positive (B+) voltage to the PCM when the brake pedal is not applied. When the brake pedal is applied, the normally closed switch opens and power is removed from the PCM.
On some applications the normally closed brake pressure switch, along with the normally open BPP switch, are used for a brake rationality test within the PCM. The PCM misfire monitor profile learn function may be disabled if a brake switch concern occurs. If one or both brake pedal inputs to the PCM is not changing states as expected, a diagnostic trouble code (DTC) is set by the PCM strategy.
Camshaft Position (CMP) Sensor
The CMP sensor detects the position of the camshaft. The CMP sensor identifies when piston number 1 is on its compression stroke. A signal is then sent to the PCM and used for synchronizing the sequential firing of the fuel injectors. Coil on plug (COP) ignition applications use the CMP signal to select the correct ignition coil to fire.
Inline engines with 2 camshafts and with variable camshaft timing (VCT) are equipped with 2 CMP sensors. The second sensor identifies the position of the exhaust camshaft.
The 2 sensor system on inline engines use the following CMP signal circuit names:
- CMP11 - bank 1, intake camshaft
- CMP12 - bank 1, exhaust camshaft
Engines with 1 camshaft per bank and with VCT are equipped with 2 CMP sensors. The second sensor identifies the position of the camshaft on bank 2.
The 2 sensor system on engines with 1 camshaft per bank and with VCT use the following CMP signal circuit names:
- CMP1 - bank 1
- CMP2 - bank 2
Engines with 4 camshafts and with VCT are equipped with 4 CMP sensors. The 4 sensors identify the position of each camshaft.
The 4 sensor system uses the following CMP signal circuit names:
- CMP11 - bank 1, intake camshaft
- CMP12 - bank 1, exhaust camshaft
- CMP21 - bank 2, intake camshaft
- CMP22 - bank 2, exhaust camshaft
There are the 2 types of CMP sensors used. The 2 pin variable reluctance sensor and the 3 pin Hall effect sensor.
Charge Air Cooler Temperature (CACT) Sensor
The CACT sensor is located in the intake air tube between the charge air cooler (CAC) and the throttle body. The CACT sensor measures the throttle inlet temperature. The PCM uses the CACT sensor information to refine the estimate of the airflow rate through the throttle and to determine the desired boost pressure. The CACT sensor for a speed density system is integrated with the turbocharger boost pressure (TCBP) sensor.
Check Fuel Cap Indicator
The check fuel cap indicator is a communications network message sent by the PCM. The PCM sends the message to illuminate the lamp when the strategy determines there is a concern in the EVAP system due to the fuel filler cap or capless fuel tank filler pipe not being sealed correctly. This is detected by the inability to pull vacuum in the fuel tank after a fueling event.
Clutch Pedal Position (CPP) Switch
The CPP switch is an input to the PCM indicating the clutch pedal position. The PCM provides a low current voltage on the CPP circuit. When the CPP switch is closed, this voltage is pulled low through the signal return (SIGRTN) circuit. The CPP input to the PCM is used to detect a reduction in engine load. The PCM uses the load information for mass airflow and fuel calculations.
Coil On Plug (COP)
The COP ignition operates similar to a standard coil pack ignition except each plug has 1 coil per plug. The COP operates in engine crank, engine running and camshaft position failure mode effects management (FMEM) modes. The COP eliminates the need for secondary spark plug wires which improves reliability. Currently there are two types of COP in use today. The first type of COP is a 2 circuit system that consists of the coil and boot that is installed directly on top of the spark plug which is fired by a driver located in the PCM. The second type COP is a 3 circuit system with the driver integrated in the COP assembly that is triggered when the PCM supplies the signal to fire. This configuration eliminates the need for high current lines from the PCM to the COP. For additional information, refer to Ignition Systems.
Coil Pack
The PCM provides a grounding switch for the coil primary circuit. When the switch is closed, voltage is applied to the coil primary circuit. This creates a magnetic field around the primary coil. The PCM opens the switch, causing the magnetic field to collapse, inducing the high voltage in the secondary coil windings and firing the spark plug. The spark plugs are paired so that as 1 spark plug fires on the compression stroke, the other spark plug fires on the exhaust stroke. The next time the coil is fired the order is reversed. The next pair of spark plugs fire according to the engine firing order.
Coil packs come in 4-tower, 6-tower horizontal and 6-tower series 5 models. Two adjacent coil towers share a common coil and are called a matched pair. For 6-tower coil pack (6 cylinder) applications, the matched pairs are 1 and 5, 2 and 6, and 3 and 4. For 4-tower coil pack (4 cylinder) applications, the matched pairs are 1 and 4 and 2 and 3.
When the coil is fired by the PCM, spark is delivered through the matched pair towers to their respective spark plugs. The spark plugs are fired simultaneously and are paired so that as one fires on the compression stroke, the other spark plug fires on the exhaust stroke. The next time the coil is fired, the situation is reversed. The next pair of spark plugs fire according to the engine firing order.
Cooling Fan Clutch
The cooling fan clutch is an electrically actuated viscous clutch that consists of 3 main elements:
- a working chamber
- a reservoir chamber
- a cooling fan clutch actuator valve and a fan speed sensor (FSS)
The cooling fan clutch actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, shearing of the fluid results in fan rotation. The cooling fan clutch actuator valve is activated with a pulse width modulated (PWM) output signal from the PCM. By opening and closing the fluid port valve, the PCM can control the cooling fan speed. The cooling fan speed is measured by a Hall effect sensor and is monitored by the PCM during closed loop operation.
The PCM optimizes fan speed based on engine coolant temperature, engine oil temperature, transmission fluid temperature, intake air temperature, or air conditioning requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM monitors the fan speed through the Hall effect sensor. If a fan speed increase is required, the PCM outputs the PWM signal to the fluid port, providing the required fan speed increase.
Cooling Fan Control
The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C ON/OFF status, A/C pressure) to determine engine cooling fan needs.
For Edge, Flex, Focus, Fusion, MKS, MKT, MKX, MKZ, Taurus, variable speed electric fans:
The PCM controls the fan speed and operation using a duty cycle output on the fan control variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor).
The fan controller has the capability to detect certain failure modes within the fan motors. Under certain failure modes, such as a motor that is drawing excessive current, the fan controller shuts OFF the fans. Fan motor concerns may not set a specific DTC. With the fan motor disconnected from the fan controller, voltage may not be present at the fan controller.
EDGE, FLEX, FOCUS, FUSION, MKS, MKT, MKX, MKZ, TAURUS: FCV DUTY CYCLE OUTPUT FROM PCM (negative duty cycle)
For Mustang, F-150, Navigator, Expedition, Escape, Transit Connect, relay controlled fans:
The PCM controls the fan operation through the fan control (FC), (single speed fan applications), low fan control (LFC) and high fan control (HFC) outputs. Some applications have the xFC circuit wired to 2 separate relays.
For 2-speed fans, although the PCM output circuits are called low and high fan control, cooling fan speed is controlled by a combination of these outputs. Refer to the following tables.
TRANSIT CONNECT (with A/C): PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS
2.5L ESCAPE: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS
MUSTANG: PCM FC OUTPUT STATE FOR COOLING FAN SPEEDS
Crankshaft Position (CKP) Sensor
The CKP sensor is a magnetic transducer mounted on the engine block adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP sensor is the primary sensor for ignition information to the PCM. The pulse wheel for some V6 engines and V8 engines have a total of 35 teeth spaced 10 degrees apart with 1 empty space for a missing tooth. The pulse wheel for some 4 cylinder engines and some V6 engines have a total of 58 teeth spaced 6 degrees apart with 2 empty spaces. The 6.8L 10 cylinder pulse wheel has 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring the pulse wheel, the CKP sensor signal indicates crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP sensor is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to a fixed reference for the CKP sensor configuration. The PCM also uses the CKP sensor signal to determine if a misfire has occurred by measuring rapid decelerations between teeth.
There are the 2 types of CKP sensors used. The 2 pin variable reluctance sensor and the 3 pin Hall effect sensor.
Cylinder Head Temperature (CHT) Sensor
Note: If the CHT sensor is removed from the cylinder head for any reason it must be replaced with a new sensor.
The CHT sensor is a thermistor device in which resistance changes with the temperature. The electrical resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor (pull-up resistor) in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The CHT sensor is installed in the cylinder head and measures the metal temperature. The CHT sensor provides complete engine temperature information and is used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system concern, such as low coolant or coolant loss, could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information, refer to Powertrain Control Software for Fail-Safe Cooling Strategy.
