Part 1
ENGINE CONTROL COMPONENTSNOTE: Transmission inputs, which are not described are discussed in the applicable Vehicle System transmission section.
Accelerator Pedal Position (APP) Sensor
The APP sensor is an input to the powertrain control module (PCM) and is used to determine the torque demand. There are 3 pedal position signals in the sensor. Signal 1, APPS1, has a negative slope (increasing angle, decreasing voltage) and signals 2 and 3, APPS2 and APPS3, both have a positive slope (increasing angle, increasing voltage). During normal operation APPS1 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 1 signal has a concern. There are 2 reference voltage circuits and 2 signal return circuits for the sensor.
Air Conditioning (A/C) Clutch Relay (A/CCR)
NOTE: The PCM PIDs WAC and wide open throttle air conditioning cutoff fault (WACF) 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 is OK, 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 Heating and Air Conditioning, Climate Control System. Also, refer to the applicable Vehicle/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.
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
A/C Evaporator Temperature (ACET) Sensor Voltage And Resistance:
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, improve defrost/demist performance, and reduce A/C clutch cycling.
NOTE: These values can vary 15% due to sensor and VREF variations. Voltage values were calculated for VREF equals 5.0 volts.
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 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.
Air Conditioning Pressure (ACP) Transducer Sensor
A/C Pressure Transducer Sensor Output Voltage:
Typical 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.
Brake Pedal Position (BPP) Switch
Typical BPP Switch:
The BPP switch is sometimes referred to stoplamp switch. The BPP switch provides a signal to the PCM indicating that 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.
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
Typical Synchronizer Hall-Effect CMP Sensor:
Typical Variable Reluctance 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 2 CMP sensors are equipped with variable camshaft timing (VCT). They use the second sensor to identify the position of the camshaft on bank 2 as an input to the PCM.
There are 2 types of CMP sensors: the 3-pin connector Hall-effect type sensor and the 2-pin connector variable reluctance type sensor.
Canister Vent (CV) Solenoid
Typical 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.
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 that there is a failure in the vapor management system due to the fuel filler cap not being sealed correctly. This would be detected by the inability to pull vacuum in the fuel tank, after a fueling event.
Clutch Pedal Position (CPP) Switch
Typical 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.
Coil On Plug (COP)
Typical 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).
Coil Pack
Typical Four-Tower Coil Pack:
Typical Six-Tower 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 series 5 6-tower 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
Cooling Fan Clutch With Fan Speed Sensor (FSS):
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 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.
Crankshaft Position (CKP) Sensor
Typical 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 deceleration between teeth.
Cylinder Head Temperature (CHT) Sensor
Typical 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.
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) 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 - Tube Mounted
Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor - Tube Mounted:
The tube mounted differential pressure feedback EGR sensor is identical in operation as the large 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.
Electric Exhaust Gas Recirculation (EEGR) Valve
EEGR Motor/Valve Assembly:
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).
Electronic Throttle Actuator Control (TAC)
The electronic TAC is a DC motor controlled by the PCM (requires 2 wires). The gear ratio from the motor to the throttle plate shaft is 17:1. There are 2 designs for the TAC, parallel and in-series. 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-series design has a separate motor housing. Two springs are used; one is used to close the throttle (main spring) and the other is in a plunger assembly that results in a default angle when no power is applied. The force of the plunger spring is 2 times stronger than the main spring. The default angle is usually set to result in a top vehicle speed of 48 km/h (30 mph). Typically this throttle angle is 7 to 8 degree from the hard stop angle. The closed throttle plate hard stop is used to prevent the throttle from binding in the bore (~ 0.75 degree). This hard stop setting is not adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
Electronic Throttle Body (ETB) Position Sensor
The ETB position sensor has 2 signal circuits in the sensor for redundancy. The redundant ETB position signals are required for increased monitoring. The first ETB 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). During normal operation the negative slope ETB position sensor signal (TP1) is used by the control strategy as the indication of throttle position. The 2 ETB 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.
Engine Coolant Temperature (ECT) Sensor
Typical Thread Type ECT Sensor:
The ECT 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 changes 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 a 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 ECT measures the temperature of the engine coolant. The PCM uses the ECT input for fuel control and for cooling fan control. There are 3 types of ECT sensors, threaded, push-in, and twist-lock. The ECT sensor is located in an engine coolant passage.
Engine Oil Temperature (EOT) Sensor
Typical EOT Sensor:
The EOT 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 changes 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 a 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 EOT sensor measures the temperature of the engine oil. The sensor is typically threaded into the engine oil lubrication system. The PCM can use the EOT sensor input to determine the following:
- On variable camshaft timing (VCT) applications the EOT input is used to adjust the VCT control gains and logic for camshaft timing.
- The PCM can use EOT sensor input in conjunction with other PCM inputs to determine oil degradation.
- The PCM can use EOT sensor input to initiate a soft engine shutdown. To prevent engine damage from occurring as a result of high oil temperatures, the PCM has the ability to initiate a soft engine shutdown. Whenever engine RPM exceeds a calibrated level for a certain period of time, the PCM begins reducing power by disabling engine cylinders.
Evaporative Emission (EVAP) Canister Purge Valve
Typical EVAP Canister Purge Valve:
NOTE: The EVAP canister purge valve may also be referred to as a vapor management valve (VMV).
The EVAP canister purge valve is part of the enhanced EVAP system that is controlled by the PCM. This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP canister purge valve is a normally closed valve. The EVAP canister purge valve controls the flow of vapors by way of a solenoid, eliminating the need for an electronic vacuum regulator and vacuum diaphragm. The PCM outputs a signal between 0 mA and 1,000 mA to control the EVAP canister purge valve.
Exhaust Gas Recirculation (EGR) Orifice Tube Assembly
EGR Orifice Tube Assembly:
The orifice tube assembly is a section of tubing connecting the exhaust system to the intake manifold. The assembly provides the flow path for the EGR to the intake manifold and also contains the metering orifice and 2 pressure pick-up tubes. The internal metering orifice creates a measurable pressure drop across it as the EGR valve opens and closes. This pressure differential across the orifice is picked up by the differential pressure feedback EGR sensor which provides feedback to the PCM.
Exhaust Gas Recirculation (EGR) System Module (ESM)
ESM:
The ESM is an integrated differential pressure feedback EGR system that functions in the same manner as a conventional differential pressure feedback EGR system. The various system components have been integrated into a single component called the ESM. The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the metering 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). This MAP signal is used for EGR correction and inferred barometric pressure (BARO) at key on. The system provides the powertrain control module (PCM) with a differential pressure feedback EGR signal, identical to a traditional differential pressure feedback EGR system.
Exhaust Gas Recirculation (EGR) Vacuum Regulator Solenoid
EGR Vacuum Regulator Solenoid:
Vacuum Output (IN-HG):
EGR Vacuum Regulator Solenoid Data:
The EGR vacuum regulator solenoid is an electromagnetic device used to regulate the vacuum supply to the EGR valve. The solenoid contains a coil which magnetically controls the position of a disc to regulate the vacuum. As the duty cycle to the coil increases, the vacuum signal passed through the solenoid to the EGR valve also increases. Vacuum not directed to the EGR valve is vented through the solenoid vent to atmosphere. Note that at 0% duty cycle (no electrical signal applied), the EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open the EGR valve.
Exhaust Gas Recirculation (EGR) Valve
Typical EGR Valve:
EGR Flowrate:
The EGR valve in the differential pressure feedback EGR system is a conventional, vacuum-actuated. The valve increases or decreases the flow of EGR. As vacuum applied to the EGR valve diaphragm overcomes the spring force, the valve begins to open. As the vacuum signal weakens, at 5.4 kPa (1.6 in-Hg) or less, the spring force closes the valve. The EGR valve is fully open at about 15 kPa (4.5 in-Hg).
Since EGR flow requirement varies greatly, providing repair specifications on flow rate is impractical. The on board diagnostic (OBD) system monitors the EGR valve function and triggers a diagnostic trouble code (DTC) if the test criteria is not met. The EGR valve flow rate is not measured directly as part of the diagnostic procedures.