Powertrain Controls - ECM/PCM

Code 34 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 4.0 - 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. Code 33 will set when:

^ Engine is running less than 1200 rpm.
^ MAP signal 15 % of BARO for 1 second.
OR
^ TPS is greater than 10 %.
^ Signal is 15 % of BARO for 1 second.

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

3. The "Scan" tool may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and circuit 432 are OK.


DIAGNOSTIC AIDS:



DIAGNOSTIC AIDS:


^ An intermittent on circuit 416 or circuit 432 can cause a Code 34.

^ 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.

^ 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.