DTC 34

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. 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: The numbers below refer to circled numbers on the diagnostic chart.

1. A Code 34 will set when:
a. A Code 21 is not being detected.
b. MAP signal voltage is too low.
c. MAP reading less than 14 kPa.
d. Engine speed is over 1200 rpm.
e. TPS is less than 20%.

2. Jumpering harness terminals "B" to "C" (5.0 volts to signal circuit) will determine if the sensor is at fault, or if there is a problem with the ECM or wiring. Be sure to cycle the ignition switch before checking the "Scan" tool reading because the value will not ne updated unless this step is followed.

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. An internally shorted TPS sensor will cause a Code 34.
3. A Code 34 will result if circuits 416 or 432 are open or shorted to ground.
4. If a Code 34 is intermittent, see DIAGNOSIS BY SYMPTOM.