General System Description

GENERAL SYSTEM OPERATION
The Engine Control System consists of various sensors, switches, and a Powertrain Control Module (PCM). These sensors and switches act as inputs to the PCM.

The sensors and switches (inputs) send the PCM data concerning engine operating conditions. The PCM interprets this data in order to control the various output devices that affect air intake amounts, the amount of fuel injection, fuel injection timing, evaporative emissions, idle-up, deceleration, ignition timing, (A/T) 3-4 shift and torque converter lockup operation. The PCM has varying amounts of control over these (outputs).

By controlling these outputs, the PCM can meet the different operational and driveability needs of the engine as the engine experiences different operating conditions and requirements.

System Input Devices
- A/C Signal
- Camshaft Position Sensor
- Camshaft Position Signal (from Ignition Control Module)
- Data Link Connector (Test Mode Signal, for Self Diagnosis Initiation)
- Exhaust Gas Recirculation (EGR) Differential Pressure Feedback (PFE) Sensor
- Engine Coolant Temperature Sensor
- Fuel Pump Monitor Signal
- Heated Oxygen Sensors (RH-LH)
- Ignition Diagnostic Monitor Signal (from Ignition Control Module)
- Intake Air Temperature Sensor
- Mass Air Flow Sensor
- Octane Adjust Shorting Bar
- Park/Neutral Position Switch (A/T)
- Park/Neutral and Clutch Pedal Position Switch (M/T)
- Stop Light Switch
- Throttle Position Sensor
- Vehicle Speed Sensor

System Output Devices
- Data Link Connector (Self Diagnosis Function, output to Super STAR II Tester)
- EGR Vacuum Regulator Solenoid
- Fuel Injector
- Fuel Pump Relay
- Idle Air Control Solenoid
- Ignition Control Module (Electronic Spark Advance)
- Purge Solenoid Valve (for Charcoal Canister purge)
- Spark Output (SPOUT) Signal (to Ignition Control Module)
- Torque Converter Clutch Solenoid (A/T only)
- Wide Open Throttle (WOT) A/C Cutout Relay
- 3-4 Shift Solenoid Valve (A/T only)

DIAGNOSTIC SELF TEST
The diagnostic self test is divided into six separate tests. They are the;
- KEY ON ENGINE OFF TEST
- KEY ON ENGINE RUNNING TEST
- DYNAMIC RESPONSE TEST
- CYLINDER BALANCE TEST
- OUTPUT STATE DIAGNOSTIC TEST
- CONTINUOUS self test (Wiggle Test)
The self test is not a conclusive test by itself, but is used as a part of the functional check. The processor stores the self test program in its permanent memory. When activated, it checks the EEC-IV system by testing its memory integrity and processing capability, and verifies that various sensors and actuators are connected and operating properly.
The KEY ON ENGINE OFF and KEY ON ENGINE RUNNING self tests are functional tests which only detect faults present at the time of the self test. Continuous self test is an ongoing test that stores fault information in Keep Alive Memory for retrieval at a later time if necessary.

FAIL SAFE MODE
Fail Safe Mode is a back-up strategy in the Powertrain Control Module designed to maintain vehicle operation if one or more inputs fail. When a sensor input is perceived to be out of limits by the PCM, an alternative strategy will be initiated.
The PCM will substitute a fixed in limit sensor value and will continue to monitor the faulty sensor input. If the faulty sensor begins to again operate within limits, the PCM will return to normal engine running strategy.
When the vehicle is operating in Fail Safe Mode, the MALFUNCTION INDICATOR LAMP will be On and a code 998 will be displayed during self test.