General Operation

Computerized Engine Control Component Tree:

The PCM determines current engine operating conditions by interpreting inputs from various sensors and switches.

The PCM then actuates various output devices to achieve the best compromise between power, fuel consumption, and emissions.

MODES OF OPERATION

Open Loop Modes

Note: In OPEN LOOP modes the PCM receives input signals and controls outputs according to preset programming. The PCM Ignores Oxygen (HO2S) sensor input during OPEN LOOP modes.

- Ignition Switch ON (Zero RPM)
- Engine Start-Up
- Engine Warm-Up
- Wide Open Throttle (WOT)
- Ignition Switch OFF
- Limp In Mode


Closed Loop Modes

Note: In CLOSED LOOP modes the PCM monitors the Oxygen Sensor (HO2S), input, and adjusts injector pulse width to compensate for operating conditions.

- Warm Idle
- Cruise
- Acceleration (Except Wide Open Throttle)
- Deceleration


SELF DIAGNOSIS OPERATION

The PCM also monitors many of its input and output circuits for faults, and if a fault is detected:

- A Diagnostic Trouble Code (DTC) is stored in memory.

- The MIL is illuminated [1].

- The vehicle enters "Limp-in Mode". SEE LIMP-IN OPERATION.

Note: DTC's can be read using the Malfunction Indicator Lamp (MIL), (previously called the Check Engine Lamp), or a scan tool. SEE Testing and Inspection.

[1] The MIL is not illuminated for every fault, always read DTC's before attempting to diagnose a driveablity or emission related problem.

INPUTS

Air Conditioning Switch/Air Conditioning Low Pressure Switch
Battery Voltage Sense
Brake Switch
Coolant Temperature Sensor (CTS)
Detonation Sensor
Diagnostic Connector
Engine Speed (Distributor Pick-up)
Heated Oxygen Sensor
Manifold Absolute Pressure (MAP) Sensor
Park/Neutral Switch (Automatic Transmission)
Speed Control Input Receive
Throttle Position Sensor (TPS)
Vehicle Distance (Speed) Sensor (VSS)

OUTPUTS

Air Conditioner Clutch Relay
Alternator Field
Idle Air Control (IAC) Motor
Automatic Shutdown (ASD) Relay
Barometric Read Solenoid
Canister Purge Solenoid
Check Engine Lamp (CEL)
Diagnostic Connector
Fuel Injector Pulse Width
Ignition Coil
Part Throttle Unlock (PTU) Solenoid (Automatic Transmission)
Radiator Fan Relay
Waste Gate Solenoid
Speed Control Solenoids
Tachometer Output