Powertrain Controls - ECM/PCM

Code 34 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 (WOT). Signals will vary depending on altitude. A "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 MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.


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

1. Code 34 will set when:
a. MAP sensor signal is too low (less than 12 kPa or greater than 26 inches of Hg.) for less than one second or the engine is running greater than 1000 rpm.
b. The engine is running less than 1000 rpm.
c. TPS is greater than 21%.

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

3. The "Scan" tool may not display 5.0 volts, but the ECM recognizes the voltage as more than 4.0 volts, indicating that the ECM and circuit 432 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. CHART C-1D can also be used to test the MAP sensor. Check all connections. Disconnect sensor from the bracket and twist the sensor by hand to check for an intermittent connection. Output changes greater than 0.1 volt indicates a bad connector or connection. If OK, replace sensor.
3. If an intermittent open in circuit 432 or 416 exist, a Code 34 will be stored.
4. If a Code 34 is intermittent, see DIAGNOSIS BY SYMPTOM.