Part 2 of 2

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. Jumpering harness terminals "B" to "C" (5 volts to signal circuit), will determine if the sensor is at fault, or if there is a problem with the ECM or wiring.

The "SCAN" tool may not display 5 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM CKT's 432 and 416 are OK.

2. This step determines if CKT 416 or CKT 432 is faulty. The Scan tool will not display battery voltage, but should indicate over 4 volts.

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 Code 33 is intermittent, Testing and Inspection