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.
1991 Geo Metro Base, 2D Hatchback, AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Diagnostic Code Charts
- Diagnostic Circuit Check
- Chart A-1, No Check Engine Light
- Diagnostic Aids
- Chart A-2, Won't Flash Code 12 Check Engine Light On Steady
- Code 13, O2 Sensor Circuit Signal Voltage Doesn't Change
- Code 14, Coolant Temp. Circuit Low Temp. Indicated
- Code 15, Coolant Temp. Sensor Circuit High Temp. Indicated
- Code 21, Throttle Switch Circuit (M/T Only) Idle Switch & Wot Switch Indicated On
- Code 21, Throttle Position Sensor Circuit (A/T) Signal Voltage High
- Code 22, Throttle Position Sensor Circuit (A/T) Signal Voltage Low
- Code 23, Intake Air Temp Sensor Circuit Low Temp Indicated
- Code 24, Vehicle Speed Sensor Circuit
- Code 25, Intake Air Temp Sensor Circuit High Temp Indicated
- Code 31, Map Sensor CKT Signal Voltage Low W/High Vacuum
- Code 32, Map Sensor CKT Signal Voltage High W/Low Vacuum
- CODE 41, IGNITION SIGNAL CKT, LSi STD IGN W/VAC ADVANCE
- CODE 41, IGN SIGNAL CKT NO SIGNAL, XFi W/ESC IGN SYSTEM
- CODE 42, CRANK ANGLE SENSOR CKT NO SIGNAL FOR 2 SEC. XFi W/ESA IGNITION
- CODE 51, EGR CIRCUIT (CALIFORNIA & XFi ONLY)
- Summary
Factory Service Tools
Use the Manual With the Right Hardware
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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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