Part 1 of 2

Code Chart 33:

MAP 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 to 1.5 volts at closed throttle (idle), to 4.5 volts at Wide Open Throttle (WOT) (low vacuum).

If the MAP sensor fails, the Engine Control Module (ECM) will substitute a fixed MAP value based on engine RPM.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

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

^ MAP signal indicates greater than 3.7 volts (80 kPa).
^ Throttle position is less than 5%.
^ These conditions exist for a time longer than 5 seconds.
OR
^ MAP signal indicates less than .3 volt (15 kPa).

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) stored.

DIAGNOSTIC AIDS:
With the ignition "ON" and the engine stopped, 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. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be within + .4 volt. If DTC 33 is intermittent, Testing and Inspection