Powertrain Controls - ECM/PCM

DTC 34:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The Powertrain Control Module (PCM) receives this information as a signal voltage that will vary from about 1.0 - 1.5 volts at idle to 4.0 - 4.8 volts at Wide Open Throttle (WOT).

The scan tool displays manifold pressure in kiloPascals (kPa) of pressure and voltage. Low pressure (high vacuum) indicates a low voltage while a high pressure (low vacuum) indicates a high voltage.

DIAGNOSTIC TROUBLE CODE (DTC) 34 WILL SET WHEN
MAP is less than 16 kPa, and RPM is less than 700 RPM, DTC 21 not set or MAP less than 20 kPa, RPM greater than 700 RPM, Throttle Position (TP) sensor angle greater than 26% and DTC 21 not set and all conditions met for 1 second.

ACTION TAKEN (PCM DEFAULT)
If the MAP sensor fails, the PCM will calculate a MAP value based on throttle position and engine speed (RPM). The Malfunction Indicator Lamp (MIL) will illuminate.

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

1. If the PCM recognizes the high MAP signal, the PCM and wiring are OK.

2. The Tech 1 scanner will not display 12 volts. The important thing is that the PCM recognizes the voltage as more than 4 volts, indicating that the PCM and CKT 432 are OK.

3. An intermittent open in CKT 432 or CKT 474 will result in a DTC 34.

DIAGNOSTIC AIDS
With the ignition "ON" and 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 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 +/- 0.4 volt.

Also, Chart C-1D MAP Output Check can be used to test the MAP sensor. Chart C-1D Manifold Absolute Pressure (MAP) Output Check

Refer to Diagnosis By Symptom/Intermittents. - Intermittent Malfunctions