Powertrain Controls - ECM/PCM

Code 33 Chart:

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).

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 ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. This step will determine if Code 33 is the result of a hard failure or an intermittent condition.

Code 33 will set when:

^ MAP signal 85 % of BARO for 1 second.
^ TPS less than 2%.
^ Engine misfire or a low unstable idle may set a code 33. Disconnect MAP sensor and system will go into backup mode. If the misfire or idle condition remains, see TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

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


DIAGNOSTIC AIDS:

^ 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 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 the accuracy of a suspect sensor. Readings should be the same +/- 0.4 volt.

^ A code 33 will result if circuit 476 is open.

^ If code 33 is intermittent, refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

^ Make sure electrical connection remains securely fastened. Check all connections. Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than 0.1 volt indicate a bad connector or connection. If OK, replace sensor. Refer to CHART C-1D, MAP sensor voltage output check for further diagnosis.