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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 4-4.5 volts at wide open throttle. If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the Throttle Position (TP) sensor to control fuel delivery.

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

1. A DTC 33 will set under the following conditions:

^ MAP signal less than .25 volt.
^ RPM less than 1200 or greater than 1200 with TP sensor greater than 15%.
OR
^ MAP signal greater than 3.7 volts.
^ TP sensor less than 5%.
^ These conditions exist for 5 seconds or more.

2. If the ECM recognizes the change, the ECM and CKTs 474 and 432 are OK. If CKT 452 is open, there may also be other DTC's set.

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 volts.
If CKT 474 is shorted to ground or to CKT 455, other DTC's may also be set. If DTC 33 is intermittent, Testing and Inspection