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 MANUALSCHEVROLET1991CAPRICE WAGON RWD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULEDESCRIPTION AND OPERATIONTHROTTLE BODY FUEL INJECTIONC3 SELF DIAGNOSTICS
1991 Chevrolet Caprice Wagon RWD V8-350 5.7L
C3 Self Diagnostics
1991 Chevrolet Caprice Wagon RWD V8-350 5.7LSECTION C3 Self Diagnostics
ALDL Connector:
Use a "Scan" tool or ground the diagnostic test terminal with the engine not running and the ignition switch in the "ON" position in order to retrieve codes. The "SERVICE ENGINE SOON" light will flash a Code 12 three times and then flash each code stored in memory three times, if the "Scan" tool is not used. Once all Codes are retrieved, a Code 12 will follow. New codes cannot be stored in the ECM once the diagnostics mode is activated. See DIAGNOSTIC CIRCUIT CHECK for a complete system check.
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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.