Powertrain Controls - ECM/PCM

Code 33 Chart:

Wiring Diagram For MAP Sensor:

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 4.0-4.5 volts at wide open throttle. The "Scan" tool displays manifold pressure in volts. Low pressure (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 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 when:
a. MAP sensor signal is too high, (pressure greater than 68 kPa (10.0 psi) or less than 9.0 inches of Hg.), for a time greater than 5 seconds.
b. TPS less than 4%.
c. Engine misfire or a low unstable idle may set a Code 33. Disconnect MAP sensor and the system will go into backup mode. If a misfire condition remains, see DIAGNOSIS BY SYMPTOM.

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


DIAGNOSTIC AIDS:

1. 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.
2. A Code 33 will result if circuit 455 is open.
3. CHART C-1D can also be used to test the MAP sensor.
4. If a Code 33 is intermittent, or if idle is rough or unstable, see DIAGNOSIS BY SYMPTOM.