Powertrain Controls - ECM/PCM

DTC 31 Diagnostic Chart:

MAP Sensor Circuit:

Circuit Description:
The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure (vacuum). The MAP sensor consists of a semi-conductor type pressure converting element, which converts a pressure change into an electrical change, and an electronic circuit which amplifies and corrects the electrical change. The powertrain control module (PCM) applies 5 volts to the MAP sensor. The change in the pressure, that results from the engine load and rpm changes, is converted into a voltage input that is monitored by the PCM. A low voltage input at the PCM indicates low manifold pressure, and a high voltage input at the PCM indicates high manifold pressure.

DTC 31 will set if either of the following conditions are met for at least 0.5 seconds:

(1) Voltage input at the PCM indicates very low manifold pressure.

(2) Voltage input at the PCM indicates very high manifold pressure.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

1. This checks for an open or short to ground in the YEL wire between the PCM and MAP sensor.

2. This checks for an open in the LT GRN/RED wire between the PCM and MAP sensor.

3. This checks for an open in the BRN wire between the PCM and MAP sensor, and for a faulty PCM or MAP sensor.

Diagnostic Aids:
If DTCs 22, 24 and 41 are also set, problem is in sensor ground circuit.
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect hamess connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.