General Operation

INPUT OPERATION

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

Sensor Inputs

- Engine Coolant Temperature (ECT) Sensor
- Manifold Absolute Pressure (MAP) Sensor
- Throttle Position Sensor (TPS)
- Heated Oxygen Sensor (O2S)
- Vehicle Speed Sensor (VSS)
- Distributor (Hall Effect) Pick-up
- Throttle Body Temperature Sensor

Other Inputs

- A/C Request
- Brake Switch
- Park/Neutral Switch
- Speed Control System Controls
- Self Test Input (STI)
- Battery Voltage (B+)

OUTPUT OPERATION

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

Outputs

- Air Conditioning Clutch (ACC) Relay
- Automatic Shut Down (ASD) And Fuel Pump Relays
- EVAP Canister Purge Solenoid
- Data Link (Diagnostic) Connector
- Electronic EGR Transducer (EET)
- Fuel Injector
- Generator Field
- Idle Air Control (IAC) Motor
- Ignition Coil
- Malfunction Indicator Lamp (MIL), (previously called "Check Engine" lamp)
- Radiator Fan Relay
- Speed Control (S/C) Solenoids
- Tachometer Output
- Torque Converter Clutch (TCC) Solenoid

MODES OF OPERATION

Open Loop Modes

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

NOTE: In OPEN LOOP modes the PCM receives input signals and controls outputs according to preset programming. The PCM Ignores Oxygen (H02S) sensor input during OPEN LOOP modes.

Closed Loop Modes

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

NOTE: In CLOSED LOOP modes the PCM monitors the Oxygen Sensor (O2S), input, and adjusts injector pulse width to compensate for operating conditions.

Limp In Mode (See Below)

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 DIAGNOSIS, TESTING AND INSPECTION PROCEDURES.

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