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Code Chart 33:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1.0-1.5 volts at idle, to 4.5 volts at wide open throttle. If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. A Code 33 will set if:

^ The engine is running.
^ MAP signal indicates greater than 3.7 volts (80 kPa).
^ TPS less than 5%.
^ These conditions are present for a time longer than 5 seconds.
OR
^ MAP signal indicates less than .3 volt (15 kPa).
^ Engine speed is less than 1200 rpm and TPS position is greater than 15%.

2. If the ECM recognizes the change, the ECM, and circuits 416 and 432 are OK. If CKT 455 is open, there may also be other codes stored.

DIAGNOSTIC AIDS:
With the ignition "ON" and the engine not running, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. A comparison of this BARO reading, with a known good vehicle with the same sensor, is a good way to check the accuracy of the problem sensor. BARO readings should be similar within +/- 0.4 volt.
If a Code 33 is intermittent, Testing and Inspection