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
Oxygen Sensor Heater (Prizm GSi)
- Turn ignition on. Using voltmeter, check for battery voltage on Black/Red wire at oxygen sensor. If battery voltage exists, go to step 3).
- If battery voltage does not exist, check for open circuit in Black/Red wire between oxygen sensor and EFI main relay. EFI main relay is located in fuse/relay block on left front side of engine compartment.
- Start engine. Using voltmeter, check for varying voltage at Black/Red wire at oxygen sensor. Voltage should vary from one volt to battery voltage. If voltage does not vary, check resistance of oxygen sensor heater using ohmmeter.
- Resistance should be about 3.5-14.0 ohms. Resistance will vary with temperature. If resistance is okay, check wiring to ECM. See appropriate wiring diagram in WIRING DIAGRAMS article in this section. The ECM is located in center of instrument panel, behind console. If wiring is okay, replace ECM.
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.