DTC 34

MAP Sensor Circuit:

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 1-1.5 volts at idle to 4-4.5 volts at Wide Open Throttle (WOT). Signals will vary depending on altitude.

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

Code 34 Diagnostic Chart:

Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 34 will set when:
^ No Code 21.
^ Engine speed less than 1200 rpm.
^ Signal is too low (kPa less than 14) or No Code 21.
^ Engine speed greater than 1200 rpm.
^ MAP sensor reading is less than 14 kPa.
^ TPS is greater than 15%.

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

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 CKT 432 are OK.


Diagnostic Aids
An intermittent open in CKT 432 or CKT 416 Will result in a Code 34.

With the ignition "ON," and the engine stopped 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. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same, .4 volt.

Chart C-1D Manifold Absolute Pressure (MAP) Output Checkto test the MAP sensor. If MAP sensor is suspected to be faulty. - Intermittent Malfunctions