E031

TEST CONDITIONS
Tested continuously.

FAILURE CONDITIONS
MAP value equal to or greater than 108 kPa for more than 0.2 seconds.

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Now" message on Driver Information Center (DIC);
3. AIR is diverted to the air cleaner;
4. ECM sets BARO equal to 92 kPa;
5. ECM uses a substitute MAP value based on engine RPM and throttle switch status (open or closed).

DESCRIPTION
The manifold absolute pressure sensor (MAP) is a "3-wire" sensor, a potentiometer that change resistance based upon manifold vacuum, The ECM provides a 5 volt reference on CKT 474 and ground on CKT 476. The MAP signal (CKT 432) varies between ground and 5 volts as manifold vacuum varies. As MAP decreases, voltage decreases (low engine load, high vacuum). As MAP increases, voltage increases (high engine load, low vacuum).

The ECM uses MAP sensor values as an indicator of engine load. A high MAP reading indicates heavy load and a low MAP reading indicates a light load.
Code EO31 sets when the ECM detects a MAP sensor signal too high (MAP value greater than 108 kPa).

Possible causes of Code EO31 are
1. Short to voltage on CKT 432;
2. Open from sensor to ECM on CKT 476;
3. Defective MAP sensor.

Notes on Fault Tree
1. If ECM data ED02 goes to 14-16 kPa with the sensor unplugged, the fault is at the sensor or sensor connector.
2. Checking for an open circuit from Pin A of the connector to ECM Pin F12 (ground). If the ground is open, the signal voltage will always be high.

Notes on Intermittents
Manipulate MAP sensor connector, MAP wiring, and ECM connector while observing ECM data ED02. Apply and release vacuum to the MAP sensor vacuum port using a vacuum source. If the ECM data ED02 immediately jumps to greater than 108 kPa, repair intermittent MAP sensor fault. If wiring and connectors check out OK, substitute a known good MAP sensor and retest.