Powertrain Controls - ECM/PCM

Manifold Absolute Pressure Sensor Circuit Code 34:

Circuit Description:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The control module receives this information as a signal voltage that will vary from about 1-1.5 volts at closed throttle (idle) to 4-4.6 volts at Wide Open Throttle (WOT) (low vacuum).

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 control module will substitute a fixed MAP value and use the Throttle Position (TP) Sensor to control fuel delivery.

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 12.6 kPa, conditions met for 1 second.
OR
- Engine speed is greater than 1200 rpm.
- Throttle angle over 21%.
- Manifold pressure less than 12.6 kPa, conditions met 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 PCM or wiring.

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

Diagnostic Aids:
An intermittent open in CKT 432 or CKT 474 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 PCM 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 + 0.4 volt.
Also, to test the MAP sensor, see Manifold Absolute Pressure Output Check or Intermittents. MAP Sensor Output Diagnosis - Intermittent Malfunctions

Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than 0.1 volt indicates a bad connector or connection. If OK, replace sensor.

NOTE: Make sure electrical connector remains securely fastened.

MAP Sensor Circuit (PCM):

Automatic Transmission (PCM) Circuit

MAP Circuit (VCM):

Manual Transmission (VCM)) Circuit