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.
1995 Geo Prizm Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes - 1.6L
- Introduction
- Self-Diagnostic System
- Diagnostic DTC Charts
- Notes
- On-Board Diagnostic (OBD) System Check
- Chart A1-1, No Malfunction Indicator Light
- Chart A1-2, Mil Will Not Flash Any DTCS, Or On Steady
- DTC 12, No Rpm Signal
- DTC 13, No Rpm Signal
- DTC 14, Ignition Signal Circuit No Ignition Signal
- DTC 21 (CALIFORNIA Emissions), O2S, Open Or Shorted Circuit
- DTC 21 (Federal Emissions), O2S, Open Or Shorted Circuit
- DTC 22, ECT Sensor, Open Or Shorted Circuit
- DTC 24, IAT Sensor, Open Or Shorted Circuit
- DTC 25 (CALIFORNIA Emissions), O2S, Air/Fuel Ratio Lean
- DTC 25 (Federal Emissions), O2S, Air/Fuel Ratio Lean
- DTC 26 (CALIF Emissions), O2S Circuit, Air/Fuel Ratio Rich
- DTC 26 (Federal Emissions), O2S Circuit, Air/Fuel Ratio Rich
- DTC 27 (CALIF Emissions), Sub-O2 Sensor (Sub-O2S), Open Or Shorted CKT
- DTC 31, Map Sensor, Open Or Shorted Circuit
- DTC 41, TP Sensor, Open Or Shorted Circuit
- DTC 42, VSS Circuit, Open Or Shorted Circuit
- DTC 43, Crank Signal, No Signal
- DTC 51, Switch Condition Signal
- DTC 71, EGR System (CALIF Emissions)
- 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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