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.
1994 Geo Prizm Base, StandardFACTORY OEM SERVICE PROCEDURE
Manifold Absolute Pressure (MAP) Sensor
- A malfunction in the manifold absolute pressure sensor circuit will set diagnostic trouble Codes 31 and/or 32. For testing procedures, see TESTS W/CODES article in this section. Use the following procedure to diagnose MAP sensor. If driveability problems exist, MAP sensor failure is suspected and no Codes 31 and/or 32 is set, disconnect MAP sensor connector. If driveability improves, replace MAP sensor.
- MAP sensor is located on firewall. With ignition on, check supply voltage from ECM to MAP sensor on designated wire terminal. See MAP SENSOR WIRE TERMINAL IDENTIFICATION . Reading should be approximately 5 volts.
- Disconnect vacuum hose at MAP sensor. Install hand-held vacuum pump. Turn ignition on. Check signal voltage at designated wire terminal of MAP sensor. See MAP SENSOR WIRE TERMINAL IDENTIFICATION .
- Apply vacuum, and note change in signal voltage. As vacuum reading changes, signal voltage should change. Reading should be about 1-1.5 volts at high vacuum (idle position) to 4-4.5 volts at low vacuum (full throttle position).
MAP SENSOR WIRE TERMINAL IDENTIFICATION
| Application | Supply Voltage Wire Color | Signal Voltage Wire Color |
|---|---|---|
| Prizm & Prizm LSi | Yellow | Light Green/Red |
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.