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.
Code 33B: Map Sensor (Signal Volt Lo): Notes
The MAP sensor responds to changes in manifold pressure (vacuum). The ECM receives a signal voltage from MAP sensor varying from .5-2.0 volts at idle (closed throttle) to 4-5 volts at wide open throttle. If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.
- This determines if Code 33B is result of a hard failure or an intermittent condition. Code 33B will set if:
- Engine RPM is greater than 1200 RPM.
- No Code 21A or 21B is set.
- TPS is greater than 15 percent.
- MAP signal voltage is low.
- Connecting harness terminals "B" to "C", will determine if MAP sensor is defective or if problem exist in ECM or wiring.
- Scan tester may not display 12 volts. Important thing is that ECM recognizes voltage as more than 4 volts, indicating that ECM and circuit No. 432 are okay.
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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.