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
- Mass Air Flow Sensor
- Intake Air Temperature Sensor
- Throttle Position Sensor
- Heated Oxygen Sensor
- Camshaft Position Sensor (MT Only)
- Crankshaft Position Sensor (AT Only)
- A/C Signal
- Engine Coolant Temperature Sensor
- Stop Light Switch
- Vehicle Speed Sensor
- Park/Neutral Position Switch (A/T)
- Ignition Diagnostic Monitor Signal (Ignition Control Module)
- Differential Pressure Feedback Exhaust Gas Recirculation (EGR) Sensor

System Output Devices
- Fuel Injector
- Spark Output (SPOUT) Signal (Ignition Control Module)
- Idle Air Control Solenoid
- Fuel Pump Relay
- Purge Solenoid Valve (For Charcoal Canister Purge)
- Wide Open Throttle (WOT) A/C Cutout Relay
- EGR Vacuum Regulator Solenoid
- 3-4 Shift Solenoid Valve (A/T only)
- Torque Converter Clutch Solenoid (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.