Standard Emissions

CODE 31 MANIFOLD ABSOLUTE PRESSURE SENSOR (SIGNAL VOLTS LOW)

MAP Sensor Diagnostic Chart:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure (vacuum). The Engine Control Module (ECM) applies 5.0 volts to the MAP sensor. The change in the pressure, that results from engine load and rpm changes, is converted into a voltage input that is monitored by the ECM. A low voltage reading at the ECM indicates low manifold pressure, and a high voltage reading at the ECM indicates high manifold pressure.

Diagnostic Trouble Code (DTC) 31 will set if the following condition is met for 0.2 seconds: Low voltage input at the ECM indicating intake manifold pressure below 5.3 kPa (40 mm Hg or 1.57 in Hg).

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

1. This step checks that the ECM is providing a 5.0 volt reference.
2. This step checks for the bias voltage to the MAP sensor which has a value between 4.5 and 4.9 volts. This step checks that value.

DIAGNOSTIC AIDS
Check for a clogged or pinched vacuum hose to MAP sensor.

An intermittent may be caused by a poor connection rubbed through wire insulation or a wire broken inside the insulation. Inspect ECM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.