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.
1999 Saturn SC2 L4-1.9L DOHC VIN 7FACTORY OEM SERVICE PROCEDURE
General Description
SIR SYSTEM
Refer to The SIR System in Diagrams/Diagnostic Aids/General Troubleshooting Procedures. Diagnostic Aids
CIRCUITS
Automotive Circuits are divided into three categories: power, signal (control or data), and ground circuits.
Power Circuits
Power circuits are classified as those cables that provide battery or mechanically switched battery voltages to electrical loads. Some examples of these circuits are:
^ Ignition circuits - 300, 3C
^ Battery circuits - 1A, 1B
^ Headlamp circuits - 40A, 40B, 40C
^ Defog circuits - 193, 1240, 293, 293A
Signal (Control Or Data) Circuits
Signal circuits are classified as those cables that provide signal voltages from one electrical device to another device. Examples of these signals and devices are:
^ Evaporative Emission Canister Purge Solenoid to PCM - 428
^ Fuel Level Sensor to PCM - 30, 30A, 30B
Signal wires are usually current limited by one of the devices that is attached to the wire. In the above examples the PCM and fuel gage limit the current in these circuits through the use of electronics (pull up or pull down resistors, transistors, etc.). Signal wire current levels for short circuit conditions normally do not exceed operating levels by an appreciable amount.
Ground Circuits
Ground circuits are classified as those circuits that provide a ground (zero voltage level with reference to the battery) to the electrical system. Examples of these circuits are:
^ I/P Chassis ground - 350, 250
^ PCM ground - 551
Since ground circuits are already shorted to ground, the current level is based on the electrical load resistance. Like signal circuits, ground circuit cable selection is a function of operating current.
Refer to The SIR System in Diagrams/Diagnostic Aids/General Troubleshooting Procedures. Diagnostic Aids
CIRCUITS
Automotive Circuits are divided into three categories: power, signal (control or data), and ground circuits.
Power Circuits
Power circuits are classified as those cables that provide battery or mechanically switched battery voltages to electrical loads. Some examples of these circuits are:
^ Ignition circuits - 300, 3C
^ Battery circuits - 1A, 1B
^ Headlamp circuits - 40A, 40B, 40C
^ Defog circuits - 193, 1240, 293, 293A
Signal (Control Or Data) Circuits
Signal circuits are classified as those cables that provide signal voltages from one electrical device to another device. Examples of these signals and devices are:
^ Evaporative Emission Canister Purge Solenoid to PCM - 428
^ Fuel Level Sensor to PCM - 30, 30A, 30B
Signal wires are usually current limited by one of the devices that is attached to the wire. In the above examples the PCM and fuel gage limit the current in these circuits through the use of electronics (pull up or pull down resistors, transistors, etc.). Signal wire current levels for short circuit conditions normally do not exceed operating levels by an appreciable amount.
Ground Circuits
Ground circuits are classified as those circuits that provide a ground (zero voltage level with reference to the battery) to the electrical system. Examples of these circuits are:
^ I/P Chassis ground - 350, 250
^ PCM ground - 551
Since ground circuits are already shorted to ground, the current level is based on the electrical load resistance. Like signal circuits, ground circuit cable selection is a function of operating current.
Factory Service Tools
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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.
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