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Engine Control Components
Note: Transmission inputs which are not described in this section, are discussed in the Transmission and Drivetrain section.
Accelerator Pedal Position (APP) Sensor
The APP sensor is an input to the powertrain control module (PCM) and is used to determine 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
There are two 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 two 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 input is used. There are two reference voltage circuits, two signal return circuits, and two signal circuits (a total of six circuits and pins) between the PCM and the APP sensor assembly. The reference voltage circuits and the signal return circuits are shared with the reference voltage circuit and signal return circuit used by the electronic throttle body (ETB) throttle position (TP) sensor. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then 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) Description and Operation.
2-Track APP Sensor:
Typical 2-Track APP Sensor
3-Track APP Sensor
There are three 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 APP1 is used as the indication of pedal position by the strategy. The three 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 then converts these degrees to counts, which is the input to the torque based strategy. There are two reference voltage circuits, two signal return circuits, and three signal circuits (a total of seven circuits and pins) between the PCM and the APP sensor assembly. The reference voltage circuits and the signal return circuits are shared with the reference voltage circuit and signal return circuit used by the electronic throttle body (ETB) throttle position sensor. For additional information, refer to Torque Based Electronic Throttle Control (ETC) Description and Operation.
3-Track APP Sensor:
Typical 3-Track APP Sensor
Air Conditioning (A/C) Clutch Relay (A/CCR)
Note: The PCM parameter identifiers (PIDs) wide open throttle air conditioning cutoff (WAC) and wide open throttle air conditioning cutoff fault (WAC_F) are used to monitor the A/CCR output.
The A/CCR is wired normally open. There is no direct electrical connection between the A/C switch or electronic automatic temperature control (EATC) module and the A/C clutch. The PCM receives a signal indicating that A/C is requested. For some applications, this message is sent through the communications network. When A/C is requested, the PCM checks other A/C related inputs that are available, such as A/C pressure switch and A/C cycling switch. If these inputs indicate A/C operation and the engine conditions are OK (coolant temperature, engine RPM, throttle position), the PCM grounds the A/CCR output, closing the relay contacts and sending voltage to the A/CCR.
Air Conditioning (A/C) Cycling Switch
The A/C cycling switch may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM turns off the A/C clutch. For information on the specific function of the A/C cycling switch, refer to the Climate Control System Air Conditioning System Overview. Also, refer to the applicable Wiring Diagrams for vehicle specific wiring.
If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate. For additional information, refer to wide open throttle air conditioning cutoff (WAC).
Some applications do not have a dedicated (separate) input to the PCM indicating that A/C is requested. This information is received by the PCM through the communication link.
Air Conditioning Evaporator Temperature (ACET) Sensor
The ACET sensor measures the evaporator air discharge temperature. The ACET 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 PCM sources a low current 5 volts on the ACET circuit. With SIG RTN also connected to the ACET sensor, the varying resistance changes the voltage drop across the sensor terminals. As A/C evaporator air temperature changes, the varying resistance of the ACET sensor changes the voltage the PCM detects.
The ACET sensor is used to more accurately control A/C clutch cycling and improve defrost/demist performance.
Note: These values can vary 15% due to sensor and VREF variations. Voltage values were calculated for VREF equals 5.0 volts.
A/C Evaporator Temperature (ACET) Sensor Voltage And Resistance Chart:
Air Conditioning (A/C) High Pressure Switch
The A/C high pressure switch is used for additional A/C system pressure control. The A/C high pressure switch is either dual function for multiple speed, relay controlled for electric fan applications, or single function for all others.
For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C pressure. This results in the A/C turning off, preventing the A/C pressure from rising to a level that would open the A/C high pressure relief valve.
For fan control, the normally open medium pressure contacts close at a predetermined A/C pressure. This grounds the ACPSW circuit input to the PCM. The PCM then turns on the high speed fan to help reduce the pressure.
For additional information, refer to the Climate Control System, Air Conditioning System Overview or the Wiring Diagrams.
Air Conditioning Pressure (ACP) Transducer Sensor
The ACP transducer sensor is located in the high pressure (discharge) side of the A/C system. The ACP transducer sensor provides a voltage signal to the PCM that is proportional to the A/C pressure. The PCM uses this information for A/C clutch control, fan control and idle speed control.
A/C Pressure Transducer Sensor Output Voltage Vs Pressure Chart:
Typical ACP Transducer Sensor:
Typical ACP Transducer Sensor
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 is 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 voltage (B+) when the vehicle 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.
Typical BPP Switch:
Typical BPP Switch
Brake Pedal Switch (BPS)/Brake Deactivator Switch
The BPS, also called the brake deactivator switch, is for vehicle speed control deactivation. A normally closed switch supplies battery positive voltage (B+) 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 BPS, 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 when they were expected to, 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.
Vehicles with two CMP sensors are equipped with variable camshaft timing (VCT). The second sensor is used to identify the position of the camshaft on bank 2.
There are two types of CMP sensors: the 2-pin variable reluctance type sensor and the 3-pin Hall-effect type sensor.
Typical Variable Reluctance CMP Sensor:
Typical Variable Reluctance CMP Sensor
Typical Hall-effect CMP Sensor:
Typical Hall-effect CMP Sensor
Canister Vent (CV) Solenoid
During the evaporative emissions (EVAP) leak check monitor, the CV solenoid seals the EVAP canister from the atmospheric pressure. This allows the EVAP canister purge valve to obtain the target vacuum in the fuel tank during the EVAP leak check monitor.
Typical Canister Vent (CV) Solenoid:
Typical Canister Vent (CV) Solenoid
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 SIG RTN circuit. The CPP input to the PCM is used to detect a reduction in engine load. The PCM uses the load information for mass air flow and fuel calculations.
Typical Clutch Pedal Position (CPP) Switch:
Typical Clutch Pedal Position (CPP) Switch
Coil On Plug (COP)
The COP ignition operates similar to a standard coil pack ignition except each plug has one coil per plug. The COP has 3 different modes of operation: engine crank, engine running, and CMP failure mode effects management (FMEM). For additional information, refer to Ignition Systems Ignition Systems.
Typical Coil On Plug (COP):
Typical Coil On Plug (COP)
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 one 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.
Typical Four-Tower Coil Pack:
Typical Four-Tower Coil Pack
Typical Six-Tower Coil Pack:
Typical Six-Tower Coil Pack
Cooling Fan Clutch
The cooling fan clutch is an electrically actuated viscous clutch that consists of three 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 clutch speed. The cooling fan clutch 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 (ECT), engine oil temperature (EOT), transmission fluid temperature (TFT), intake air temperature (IAT), 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 Clutch with Fan Speed Sensor (FSS):
Cooling Fan Clutch with Fan Speed Sensor (FSS)
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 is the primary sensor for ignition information to the PCM. The pulse wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. 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 signal to determine if a misfire has occurred by measuring rapid decelerations between teeth.
Typical Crankshaft Position (CKP) Sensor:
Typical Crankshaft Position (CKP) Sensor
Cylinder Head Temperature (CHT) 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.
The CHT sensor is installed in the cylinder head and measures the metal temperature. The CHT sensor can provide complete engine temperature information and can be 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 Powertrain Control Software for Fail-Safe Cooling Strategy.
Typical CHT Sensor:
Typical CHT Sensor
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor
The differential pressure feedback EGR sensor is a ceramic, capacitive-type pressure transducer that monitors the differential pressure across a metering orifice located in the orifice tube assembly. The differential pressure feedback EGR sensor receives this signal through 2 hoses referred to as the downstream pressure hose (REF SIGNAL) and upstream pressure hose (HI SIGNAL). The HI and REF hose connections are marked on the differential pressure feedback EGR sensor housing for identification (note that the HI signal uses a larger diameter hose). The differential pressure feedback EGR sensor outputs a voltage proportional to the pressure drop across the metering orifice and supplies it to the PCM as EGR flow rate feedback.
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor:
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor - Tube Mounted
The tube mounted differential pressure feedback EGR sensor is identical in operation as the larger plastic differential pressure feedback EGR sensors and uses a 1.0 volt offset. The HI and REF hose connections are marked on the side of the sensor.
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor - Tube Mounted:
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor - Tube Mounted
Electric Exhaust Gas Recirculation (EEGR) Valve
Depending on the application, the EEGR valve is a water cooled or an air cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built-in spring works to close the valve (against the motor opening force).
EEGR Motor/Valve Assembly:
EEGR Motor/Valve Assembly
Electronic Throttle Actuator Control (TAC)
The electronic TAC is a DC motor controlled by the PCM (requires 2 wires). There are 2 designs for the TAC, parallel and in-line. The parallel design has the motor under the bore parallel to the plate shaft. The motor housing is integrated into the main housing. The in-line design has a separate motor housing. An internal spring is used in both designs to return the throttle plate to a default position. The default position is typically a throttle angle of 7 to 8 degrees from the hard stop angle. The closed throttle plate hard stop is used to prevent the throttle from binding in the bore. This hard stop setting is not adjustable and is set to result in less airflow than the minimum engine airflow required at idle. For additional information, refer to Torque Based Electronic Throttle Control (ETC) Description and Operation.
Typical In-line TAC Design:
Typical In-line TAC Design
Typical Parallel TAC Design:
Typical Parallel TAC Design
Electronic Throttle Body (ETB) Throttle Position Sensor
The ETB throttle position sensor has 2 signal circuits in the sensor for redundancy. The redundant ETB throttle position signals are required for increased monitoring. The first ETB throttle position sensor signal (TP1) has a negative slope (increasing angle, decreasing voltage) and the second signal (TP2) has a positive slope (increasing angle, increasing voltage). The 2 ETB throttle position sensor signals make sure the PCM receives a correct input even if 1 signal has a concern. There is 1 reference voltage circuit and 1 signal return circuit for the sensor. The reference voltage circuit and the signal return circuit is shared with the reference voltage circuits and signal return circuits used by the APP sensor. For additional information, refer to Torque Based Electronic Throttle Control (ETC) Description and Operation.