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.
1990 Geo Storm Base, StandardFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Diagnostic Circuit Check
- Chart A-1, Won't Flash Code 12 No Check Engine Light
- Chart A-2, No ALDL Data Or Won't Flash Code 12 Check Engine Light On At All Times
- Code 13, Oxygen Sensor Circuit (Non-Heated O2 Sensor Only) Open Or Grounded Circuit
- Code 14A, Coolant Temperature Sensor (Cts) Circuit High Temperature Indicated
- Code 14B, Coolant Temperature Sensor (Cts) Circuit Low Temperature Indicated
- Code 21A, Throttle Position Sensor Circuit
- Code 21B, Throttle Position Sensor Circuit
- Code 23A, Manifold Air Temperature (Mat) Sensor Circuit Low Temperature Indicated
- Code 23B, Manifold Air Temperature (Mat) Sensor Circuit High Temperature Indicated
- Code 24, Vehicle Speed Sensor Circuit
- Code 33A, Manifold Absolute Pressure (Map) Sensor Circuit Signal Voltage High-Low Vacuum
- Code 33B, Manifold Absolute Pressure (Map) Sensor Circuit Signal Voltage Low-High Vacuum
- Code 42, Electronic Spark Timing (Est)
- Code 44, Oxygen Sensor Circuit Lean Exhaust Indicated (VIN 5)
- Code 44, Oxygen Sensor Circuit Lean Exhaust Indicated VIN 6)
- Code 45, Oxygen Sensor Circuit Rich Exhaust Indicated
- Code 51, ECM Failure ECM Failed Or Prom Failure
- 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.
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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.