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.

1. 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.
2. Connecting harness terminals "B" to "C", will determine if MAP sensor is defective or if problem exist in ECM or wiring.
3. 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.