DTC 34

Manifold Absolute Pressure Sensor Circuit Code 34:

Manifold Absolute Pressure Sensor Circuit:

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

1. This step determines if Code 34 is the result of a hard failure or an intermittent condition. A Code 34 will set when:

^ When engine is less than 1200 rpm.
^ Manifold pressure reading less than 12 kPa, for 1 second
OR
^ Engine speed is greater than 1200 rpm for 1 second.

2. Jumpering harness terminals "B" to "C" (5 volts to signal circuit) will determine if the sensor is at fault, or if there is a problem with the ECM or wiring.

3. The Tech 1 "Scan" tool may not display 5 volts. The important thing is that the ECM recognized the voltage as more than 4 volts, indicating that the ECM and CKT 432 are OK.

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 4-4.6 volts at Wide Open Throttle (WOT).

A Tech 1 "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.


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

With the ignition "ON" and the engine "OFF," 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. Comparison of this 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. Also, see Manifold Absolute Pressure (MAP) Output Check MAP Sensor Output Diagnosis to test the MAP sensor. See Intermittents - Intermittent Malfunctions

Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than .1 volt indicates a bad connector or connection. If OK, replace sensor.

NOTE: Make sure electrical connector remains securely fastened.