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.
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HOMESERVICE MANUALSGEO1993PRIZM L4-1600CC 1.6L DOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSMANIFOLD PRESSURE/VACUUM SENSORDESCRIPTION AND OPERATION
1993 Geo Prizm L4-1600cc 1.6L DOHC
Manifold Pressure/Vacuum Sensor: Description and Operation
1993 Geo Prizm L4-1600cc 1.6L DOHCSECTION Description and Operation
MAP Sensor:
MAP Sensor Output Characteristic:
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load and speed changes. The ECM converts this to a voltage output.
The ECM sends a 5.0 volts reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the manifold pressure. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires less fuel.
A closed throttle on engine coast down would produce a relatively low MAP output, while a wide-open throttle would produce a high output. MAP sensor pressure is the opposite of what would be measured on a vacuum gauge. When manifold pressure is high, vacuum is low.
The MAP sensor is also used to measure barometric pressure under certain conitions, which allows the ECM to automatically adjust for different altitudes.
A failure in the MAP sensor circuit should set a Code 31.
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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.