Electronic Engine Controls

ELECTRONIC ENGINE CONTROLS

The electronic engine controls consist of the:
- powertrain control module (PCM).
- throttle position (TP) sensor.
- idle air control (IAC) valve.
- cylinder head temperature (CHT) sensor.
- camshaft position (CMP) sensor.
- crankshaft position (CKP) sensor.
- power steering pressure (PSP) switch.
- mass air flow (MAF) sensor.
- heated oxygen sensor (HO2S).
- catalyst monitor sensor(s).
- knock sensor (KS).
- fuel rail pressure and temperature sensor.

The PCM:
- accepts input from various engine sensors to compute the fuel flow rate and spark timing necessary to maintain a prescribed air/fuel ratio throughout the entire engine operating range.
- outputs a command to the fuel injectors to meter the appropriate quantity of fuel.

The TP sensor:
- sends the PCM a signal indicating the throttle plate angle.
- is the main input to the PCM from the driver.

The IAC valve:
- controls bypass air around the throttle plate at low engine speeds.
- accommodates for small changes in engine load.
- is controlled by the PCM.

The CHT sensor:
- sends the PCM a signal indicating cylinder head temperature.
- resistance decreases as coolant temperature increases.

The CMP sensor:
- provides camshaft position information which is used by the PCM for fuel synchronization.

The CKP sensor:
- sends the PCM a signal indicating crankshaft position.
- is essential for calculating spark timing.

The PSP switch:
- is a normally closed switch that opens as pressure increases.
- is used to send a signal to the PCM to adjust idle speed. This compensates for additional load on the engine from the power steering pump.

The MAF sensor:
- uses a hot wire sensing element to measure the amount of air entering the engine.
- uses a second hot wire to measure intake air temperature.
- sends signals to the PCM. The PCM will then calculate the required fuel injector pulse width in order to provide the desired air/fuel ratio.

The HO2S:
- has the ability to create a voltage signal dependent on exhaust oxygen content.
- provides feedback information to the PCM used to calculate fuel delivery.

The catalyst monitor sensor(s):
- has the ability to create a voltage signal dependent on exhaust oxygen content.
- provides feedback information to the PCM used to calculate catalyst efficiency.

The KS:
- sends a signal to the PCM indicating engine detonation, which retards the ignition timing as necessary.

The fuel rail pressure and temperature sensor:
- measures the pressure and temperature of the fuel rail and sends these signals to the PCM.
- uses intake manifold vacuum as a pressure reference.