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.
1989 Geo Prizm Base, StandardFACTORY OEM SERVICE PROCEDURE
Trouble Code Identification Charts
PRIZM TROUBLE CODE IDENTIFICATION CHART
| Code | System Affected | Probable Cause |
|---|---|---|
| 12 & 13 | No RPM Signal | No Signal For 2 Seconds |
| 14 | Ignition Signal Circuit | No Signal |
| 21 | Oxygen Sensor Circuit | Open Or Short Circuit |
| 22 | Coolant Temperature Sensor Circuit | Open Or Short Circuit |
| 24 | Manifold Air Temperature Sensor Circuit | Low Temp. Indicated |
| 25 | Oxygen Sensor Circuit | Lean Exhaust Indicated |
| 26 | Oxygen Sensor Circuit | Rich Exhaust Indicated |
| 31 | MAP Sensor | Open Or Shorted Circuit |
| 41 | Throttle Switch Circuit | Incorrect Signal Voltage |
| 42 | Vehicle Speed Sensor Circuit | Incorrect Signal Voltage |
| 43 | No Crank Signal | No Signal From Starter |
| 51 | No A/C Signal | No Signal Present |
| 71 | EGR Gas Temperature Sensor Circuit | Out Of Calibrated Range |
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.