Powertrain Controls - ECM/PCM

Code 33 Chart:

Code 33 Wiring Diagram:

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 idle, when manifold pressure is low (high vacuum), to 4.5 - 4.8 volts at wide open throttle (low vacuum or high pressure).

A "Scan" tool displays information in volts. Low presure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.

If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.

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

1. Code 33 will set when:

- Signal is to high. (kPa greater than 68 kPa or less than 9" Hg for a time greater than 5 seconds.
- TPS less than 4%.
- Engine misfire or a low unstable may set a Code 33. Disconnect the MAP sensor and system will go into fuel backup mode. If the misfire or idle condition remains Refer to DIAGNOSIS BY SYMPTOM.

2. If the ECM recognizes the low MAP signal, the ECM and wiring are OK.


DIAGNOSTIC AIDS:

- If the idle is rough Refer to DIAGNOSIS BY SYMPTOM.
- An open in circuit 470 will result in a Code 33.
- With the ignition "ON and the engine stopped, the manifold pressure will be 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 referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check the accuracy of a "suspect" sensor. Readings should be the same +/- 0.4 volt. Also CHART C-1D can be used to check the MAP sensor