Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSATURN1991SC AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCETHEORY AND OPERATIONENGINE CONTROLS - THEORY & OPERATION
1991 Saturn SC Automatic
Engine Controls - Theory & Operation
1991 Saturn SC AutomaticSECTION Engine Controls - Theory & Operation
- Introduction
- Air Induction System
- Computerized Engine Controls
- Notes
- Electronic Control Module (ECM)
- Input Devices
- Notes
- A/C "On" Switch
- A/C Pressure Sensor
- A/C Pressure Switches
- A/C Temperature Sensors (4.9L)
- Battery Voltage
- Brake Switch Feedback
- Coolant Temperature Sensor (CTS)
- Camshaft Position Sensor (C3I System)
- Crankshaft Position Sensor
- Fuel Pump Feedback
- Gear Switches
- Handwheel Sensor (Saturn)
- Ignition/Crank Signal
- Knock Sensor
- Manifold Absolute Pressure (MAP) Sensor (Except 3.3L & 3.8L)
- Manifold Air Temperature (MAT) Sensor
- Mass Airflow (MAF) Sensor (3.3L & 3.8L)
- Oil Temperature (Engine) Sensor
- Oxygen (O2) Sensor
- Park/Neutral (P/N) Switch
- Power Steering (P/S) Pressure Switch
- RPM Reference Signal
- Throttle Position Sensor (TPS)
- Throttle Switch (4.9L)
- Vehicle Speed Sensor (VSS)
- Output Signals
- Notes
- A/C Clutch
- Air Injection Control Solenoid
- Boost Control Solenoid (Supercharger)
- Canister Purge Solenoid
- Computer Controlled Coil Ignition (C3I)
- Cooling Fan Relay
- Digital EGR Valve
- Direct Ignition System (DIS)
- EGR Control Solenoid
- Electronic Variable Orifice (EVO) Actuator
- ESC Timing Retard
- EST Timing Control
- Fuel Injectors
- Fuel Pump & Fuel Pump Relay
- HEI-EST Ignition
- HOT Light Or Coolant Temperature (TEMP) Light
- Idle Air Control (IAC) Valve
- Idle Speed Control (ISC) Motor (4.9L)
- Integrated Direct Ignition (IDI) System
- Opti-Spark System (Corvette)
- Self-Diagnostics
- Serial Data
- SERVICE ENGINE SOON Light
- Shift Light
- Torque Converter Clutch
- Fuel System
- Ignition System
- Emission Systems
- Self-Diagnostic System
- Miscellaneous Controls
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.