Computers and Control Systems: Description and Operation
1. Idle Air Control Valve (IAC)
2. Knock Sensor (KS)
3. Throttle Position Sensor (TP)
4. Intake Air Temperature Sensor (IAT)
5. Powertrain Control Module (PCM)
6. Mass Air Flow Sensor (MAF)
7. Heated Oxygen Sensor (HO2S) - Front
8. Heated Oxygen Sensor (HO2S) - Rear
9. Power Steering Pressure (PSP) Switch
10. Crankshaft Position Sensor (CKP)
11. Cylinder Head Temperature (CHT) Sensor
12. Camshaft Position Sensor (CMP)
The electronic engine controls consist of the following:
- Powertrain Control Module (PCM)
- throttle position sensor
- idle air control valve
- camshaft position sensor
- crankshaft position sensor
- mass air flow sensor
- intake air temperature sensor
- heated oxygen sensor-front
- heated oxygen sensor-rear
- knock sensor
- Cylinder Head Temperature (CHT) sensor
- Power Steering Pressure (PSP) switch
The powertrain control module needs the following inputs to calibrate the engine properly:
- camshaft position
- engine rpm
- engine coolant temperature
- amount of engine detonation
The throttle position sensor:
- sends the powertrain control module a signal indicating the throttle plate angle.
- is the main input to the powertrain control module from the driver.
The idle air control valve:
- controls bypass air around the throttle plate at low speeds.
- is controlled by the powertrain control module.
The camshaft position sensor:
- sends the powertrain control module a signal indicating camshaft position used for fuel synchronization.
The power steering pressure switch:
- Is located on the power steering pump, generates a differential pressure, and is dependent on current input.
- This differential pressure controls the spool valve in the power steering pump.
- The Power Steering Pressure Switch (PSP) regulates the hydraulic flow and, when combined with a current controlling device, yields a variable assist power steering system.
- At low speeds of 16 km/h (10 mph) or less, the power steering pressure switch is controlled to provide full power steering pump flow for full power steering assist.
- At higher vehicle speeds, the power steering pressure switch is controlled to reduce power steering pump flow and to reduce the power steering assist.
- For evasive maneuvering at high speeds (steering wheel rotation rate greater than 22 rpm), the power steering pressure Switch is controlled to increase the power steering pump flow, thereby increasing power steering assist.
The crankshaft position sensor:
- sends the powertrain control module a signal indicating crankshaft position.
- is essential for calculating spark timing.
The mass air flow sensor:
- sends the powertrain control module a signal indicating mass air flow rate of air entering the engine.
The intake air temperature sensor:
- sends the powertrain control module a signal indicating the temperature of the air entering the engine.
- resistance decreases as temperature increases.
The heated oxygen sensor:
- has the ability to create a voltage signal dependent on exhaust oxygen content.
- provides feedback information to the powertrain control module used to calculate fuel delivery.
The rear heated oxygen sensors:
- monitors oxygen content after it flows through the catalytic converter.
- provides a voltage to the powertrain control module used to calculate catalytic converter integrity.
The knock sensor:
- is located in the intake valley.
- sends a signal to the powertrain control module indicating engine detonation.
- if detonation is occurring, the powertrain control module then changes engine timing.
The CHT sensor:
- is mounted into the wall of the cylinder head and is not connected to any coolant passages.
- sends a signal to the powertrain control module indicating the cylinder head temperature.
- If the temperature exceeds approximately 121°C (250°F), the powertrain control module disables four fuel injectors at a time. The powertrain control module will alternate which fuel injectors are disabled every 32 engine cycles. The four cylinders that are not being fuel injected act as air pumps to aid in cooling the engine.
- If the temperature exceeds approximately 166°C (330°F), the powertrain control module disables all of the fuel injectors until the engine temperature drops below approximately 154°C (310°F).
- DTCs are set.
- If the engine reaches critical temperature, the following happens:
- The coolant temperature gauge pointer will read fully hot at approximately 121°C (250°F).
- The check gauge warning indicator will illuminate.
The wheel speed sensor:
- sends a signal to the powertrain control module indicating wheel speed.