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.
1992 Geo Prizm Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Summary
- Diagnostic Code Charts (Except GSI)
- Notes
- Diagnostic Circuit Check
- Chart A-1, No Check Engine Light
- Chart A-2, Check Engine Light Won't Flash, On All The Time
- Codes 12 &/Or 13, No Rpm Signal, No Signal For 2 Seconds
- Code 14, Ignition Signal Circuit, No Signal
- Code 21, Oxygen Sensor Circuit, Open Or Shorted Circuit
- Code 22, Coolant Temperature Sensor, Open Or Shorted Circuit
- Code 24, Intake Air Temp Sensor CKT, Open Or Shorted CKT
- Code 25, Oxygen Sensor Circuit Lean Exhaust Indicated
- Code 26, Oxygen Sensor Circuit Rich Exhaust Indicated
- Code 31, Map Sensor, Open Or Shorted Circuit
- Code 41, Throttle Switch Circuit
- Code 42, Vehicle Speed Sensor Circuit
- Code 43, No Crank Signal From Starter
- Code 51, Switch Condition Signal
- Code 71, EGR Temperature Sensor Circuit (CALIF. Only)
- Diagnostic Code Charts (GSI)
- Notes
- Diagnostic Circuit Check
- Chart A-1, No Check Engine Light
- Chart A-2, Check Engine Light, Won't Flash, On All The Time
- Codes 12 &/Or 13, No Rpm Signal, No Signal For 2 Seconds
- Code 14, Ignition Signal Circuit, No Signal
- Code 21, Oxygen Sensor Circuit Open Or Short Circuit (CALIF.)
- Code 21, Oxygen Sensor CKT Open Or Short CKT (Federal)
- Code 22, Coolant Temp Sensor (Cts) CKT, Open Or Shorted CKT
- Code 24, Intake Air Temp (IAT) Sensor CKT, Open Or Shorted
- Code 25, Oxygen Sensor Circuit, Lean Exhaust Indicated
- Code 26, Oxygen Sensor Circuit, Rich Exhaust Indicated
- Code 27, Sub-Oxygen Sensor CKT, Open Or Shorted CKT (CALIF.)
- Code 31, Mass Airflow Sensor, Short Circuit
- Code 41, Throttle Position Sensor (TPS), Open Or Short CKT
- Code 42, Vehicle Speed Sensor Circuit
- Code 43, No Crank Signal, No Signal From Starter
- Code 51, Switch Condition Signal
- Code 52, Knock Sensor Signal, Open Or Short Circuit
- Code 53, Knock Control Signal, Faulty ECM
- Code 71, EGR Temperature Sensor Circuit (CALIF. Only)
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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