Ou-Ve

Engine Control Components

Note: Transmission inputs which are not described in this section, are discussed in the Transmission and Drivetrain section.

Output Shaft Speed (OSS) Sensor

The OSS sensor provides the PCM with information about the rotational speed of an output shaft. The PCM uses the information to control and diagnose powertrain behavior. In some applications, the sensor is also used as the source of vehicle speed. The sensor may be physically located in different places on the vehicle, depending upon the specific application. The design of each speed sensor is unique and depends on which powertrain control feature uses the information that is generated.

Power Steering Pressure (PSP) Sensor

The PSP sensor monitors the hydraulic pressure within the power steering system. The PSP sensor voltage input to the PCM changes as the hydraulic pressure changes. The PCM uses the input signal from the PSP sensor to compensate for additional loads on the engine by adjusting the idle RPM and preventing engine stall during parking maneuvers. Also, the PSP sensor signals the PCM to adjust the transmission EPC pressure during increased engine load, for example, during parking maneuvers.

Typical Power Steering Pressure (PSP) Sensor:

Typical Power Steering Pressure (PSP) Sensor

Power Steering Pressure (PSP) Switch

The PSP switch monitors the hydraulic pressure within the power steering system. The PSP switch is a normally closed switch that opens as the hydraulic pressure increases. The PCM provides a low current voltage on the PSP circuit. When the PSP switch is closed, this voltage is pulled low through the SIG RTN circuit. The PCM uses the input signal from the PSP switch to compensate for additional loads on the engine by adjusting the idle RPM and preventing engine stall during parking maneuvers. Also, the PSP switch signals the PCM to adjust the transmission EPC pressure during increased engine load, for example during parking maneuvers.

Typical Power Steering Pressure (PSP) Switch:

Typical Power Steering Pressure (PSP) Switch

Power Take-Off (PTO) Switch and Circuits

The PTO circuit is used by the PCM to disable some of the on board diagnostics (OBD) monitors during PTO operation. The PTO switch is normally open. When the PTO unit is activated, the PTO switch is closed and battery voltage is supplied to the PTO input circuit. This indicates to the PCM that an additional load is being applied to the engine. The PTO indicator lamp illuminates when the PTO system is functioning correctly and flashes when the PTO system is damaged.

When the PTO unit is activated, the PCM disables some OBD monitors which may not function reliably during PTO operation. Without the PTO circuit information to the PCM, false DTCs may be set during PTO operation. Prior to an Inspection/Maintenance (I/M) test, operate the vehicle with the PTO disengaged long enough to successfully complete the OBD Monitors.

PTO Circuits Description

The three 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.

Powertrain Control Module - Vehicle Speed Output (PCM-VSO)

The PCM-VSO speed signal subsystem generates vehicle speed information for distribution to those electrical/electronic modules and subsystems that require vehicle speed data. This subsystem senses the transmission OSS with a sensor. The data is processed by the PCM and distributed as a hardwired signal or as a message on the vehicle communication network.

The key features of the PCM-VSO system are to:

- infer vehicle movement from the OSS sensor signal.

- convert transmission output shaft rotational information to vehicle speed information.

- compensate for tire size and axle ratio with a programmed calibration variable.

- use a transfer case speed sensor (TCSS) for four wheel drive (4WD) applications.

- distribute vehicle speed information as a multiplexed message and/or an analog signal.

The signal from a non-contact shaft sensor OSS or TCSS mounted on the transmission (automatic, manual, or 4WD transfer case) is sensed directly by the PCM. The PCM converts the OSS or TCSS information to 8,000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into the PCM at the time the vehicle is assembled and can be reprogrammed in the field for servicing changes in the tire size and axle ratio. The PCM transmits the computed vehicle speed and distance traveled information to all the vehicle speed signal users on the vehicle. VSO information can be transmitted by a hardwired interface between the vehicle speed signal user and the PCM, or by a speed and odometer data message through the vehicle communication network data link.

The PCM-VSO hardwired signal wave form is a DC square wave with a voltage level of 0 to VBAT. Typical output operating range is 1.3808 Hz per 1 km/h (2.22 Hz per mph).

Secondary Air Injection (AIR) Bypass Solenoid

The secondary AIR bypass solenoid is used by the PCM to control vacuum to the secondary air injection diverter (AIR diverter) valve. The secondary AIR bypass solenoid is a normally closed solenoid. The secondary AIR bypass solenoid also has a filtered vent feature to permit vacuum release.

Secondary AIR Bypass Solenoid:

Secondary AIR Bypass Solenoid

Secondary AIR Diverter Valve

The secondary AIR diverter valve is used with the secondary AIR pump to provide on/off control of air to the exhaust manifold and catalytic converter. When the secondary AIR pump is on and vacuum is supplied to the AIR diverter valve, air passes the integral check valve disk. When the secondary AIR pump is off, and vacuum is removed from the AIR diverter valve, the integral check valve disk is held on the seat and stops air from being drawn into the exhaust system and prevents the back flow of the exhaust into the secondary AIR system.

Secondary AIR Diverter Valve:

Secondary AIR Diverter Valve

Secondary AIR Pump

The secondary AIR pump provides pressurized air to the secondary AIR system. The secondary AIR pump functions independently of RPM and is controlled by the PCM. The secondary AIR pump is only used for short periods of time. Delivery of air is dependent on the amount of system backpressure and system voltage. The secondary AIR pump draws dry filtered air from the intake air system downstream of the mass air flow/intake air temperature sensor. For additional information on the secondary AIR injection system, refer to Secondary Air Injection (AIR) System Description and Operation.

Secondary Air Pump:

Secondary Air Pump

Starter Motor Request (SMR) Circuit

The SMR circuit provides the PCM with a signal from the ignition switch to the PCM. The input is pulled high when the ignition is in the START position and the transmission range sensor ignition lockout circuit allows the starter to engage.

Throttle Position (TP) Sensor

The TP sensor is a rotary potentiometer sensor that provides a signal to the PCM that is linearly proportional to the throttle plate/shaft position. The sensor housing has a 3-blade electrical connector that may be gold plated. The gold plating increases the corrosion resistance on the terminals and increases the connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, four operating conditions are determined by the PCM from the TP. These are:

- closed throttle (includes idle or deceleration)

- part throttle (includes cruise or moderate acceleration)

- wide open throttle (includes maximum acceleration or de-choke on crank)

- throttle angle rate

Typical TP Sensor:

Typical TP Sensor

Transmission Control Indicator Lamp (TCIL)

The TCIL is an output signal from the PCM that controls the lamp on/off function depending on the engagement or disengagement of overdrive.

Transmission Control Switch (TCS)

The TCS signals the PCM with VPWR whenever the TCS is pressed. On vehicles with this feature, the transmission control indicator lamp (TCIL) illuminates when the TCS is cycled to disengage overdrive.

Typical Transmission Control Switch (TCS) (Column Shift):

Typical Transmission Control Switch (TCS)

Typical Transmission Control Switch (TCS) (Floor Shift):

Typical Transmission Control Switch (TCS)

Universal Heated Oxygen Sensor (HO2S)

The universal HO2S, sometimes referred to as a wideband oxygen sensor, uses the typical HO2S combined with a current controller in the PCM to infer an air/fuel ratio relative to the stoichiometric air/fuel ratio. This is accomplished by balancing the amount of oxygen ions pumped in or out of a measurement chamber within the sensor. The typical HO2S within the universal HO2S is used to detect the oxygen content of the exhaust gas in the measurement chamber. The oxygen content inside the measurement chamber is maintained at the stoichiometric air/fuel ratio by pumping oxygen ions in and out of the measurement chamber. As the exhaust gasses get richer or leaner, the amount of oxygen that must be pumped in or out to maintain a stoichiometric air/fuel ratio in the measurement chamber varies in proportion to the air/fuel ratio. The amount of current required to pump the oxygen ions in or out of the measurement chamber is used to measure the air/fuel ratio. The measured air/fuel ratio is actually the output from the current controller in the PCM and not a signal that comes directly from the sensor.

The universal HO2S also uses a self-contained reference chamber to make sure an oxygen differential is always present. The oxygen for the reference chamber is supplied by pumping small amounts of oxygen ions from the measurement chamber into the reference chamber. The universal HO2S does not need access to outside air.

Part to part variance is compensated for by placing a resistor in the connector. This resistor is used to trim the current measured by the current controller in the PCM.

Embedded with the sensing element is the universal HO2S heater. The heater allows the engine to enter closed loop operation sooner. The heating element heats the sensor to a temperature of 780°C (1,436°F). The VPWR circuit supplies voltage to the heater. The PCM controls the heater on and off by providing the ground to maintain the sensor at the correct temperature for maximum accuracy.

Vehicle Speed Sensor (VSS)

The VSS is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low speed, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling, and torque converter clutch scheduling.

Typical Vehicle Speed Sensor (VSS):

Typical Vehicle Speed Sensor (VSS)