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.
1993 Geo Prizm Base, StandardFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- DIAGNOSTIC CODE CHARTS (EXCEPT LSi)
- Notes
- Diagnostic Circuit Check
- Chart A1-1, No Malfunction Indicator Light
- Chart A1-2, Mil Won't Flash Any Codes, On Steady
- Code 12, No Rpm Signal
- Code 13, No Rpm Signal
- Code 14, Ignition Signal Circuit, No Signal
- Code 21, Oxygen Sensor Circuit, Open Or Shorted Circuit
- Code 22, Engine Coolant Temp Sensor, Open Or Shorted CKT
- Code 24, IAT Sensor Circuit, Open Or Shorted Circuit
- Code 25, O2 Sensor Circuit, Lean Exhaust Indicated
- Code 26, Oxygen Sensor Circuit, Rich Exhaust Indicated
- Code 27, Sub-O2 Sens CKT, Open Or Shorted CKT (Ca EMIS Only)
- Code 31, Map Sensor, Open Or Shorted Circuit
- Code 41, TP Sensor Circuit, Open Or Shorted Circuit
- Code 42, Vehicle Speed Sensor CKT, Open Or Shorted CKT
- Code 43, Crank Signal, No Signal
- Code 51, Switch Condition Signal
- Code 71, Exhaust Gas RECIRCULATION (EGR) SYS (Ca Emissions)
- (VIN 8) CODE CHARTS (PRIZM LSi)
- Diagnostic Circuit Check
- Chart A2-1, No Malfunction Indicator Light (Mil)
- Chart A2-2, Mil Won't Flash Any Codes, On Steady
- Code 12, No Rpm Signal
- Code 13, No Rpm Signal
- Code 14, Ignition Signal Circuit, No Signal
- Code 16, Pcm Control Signal, Pcm Failure
- Code 21, Oxygen Sensor Circuit, Open Or Shorted Circuit
- Code 22, Engine Coolant Temp Sensor, Open Or Shorted CKT
- Code 24, IAT Sensor Circuit, Open Or Shorted Circuit
- Code 25, O2 Sensor CKT, Lean Exhaust Indicated
- Code 26, O2 Sensor CKT, Rich Exhaust Indicated
- Code 27, Sub-O2 Sens CKT, Open Or Shorted CKT (Ca Emissions)
- Code 31, Map Sensor, Open Or Shorted Circuit
- Code 41, TP Sensor Circuit, Open Or Shorted Circuit
- Code 42, Vehicle Speed Sensor CKT, Open Or Shorted CKT
- Code 43, Crank Signal, No Signal
- Code 51, Switch Condition Signal
- Code 52, Knock Sensor Circuit, Open Or Shorted Circuit
- Code 71, EGR System (CALIF Emissions Only)
- Summary
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
Comes to youSame-day available12-month warranty
Get a Free QuoteNo obligation. See pricing before you book.