Action Taken

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on SERVICE SOON light.
Turn off air management solenoids.
ECM uses a substitute MAP sensor value from a table of substitute MAP versus RPM when throttle switch is closed.
ECM uses a substitute MAP sensor value of 81.8 kPa with open throttle switch.
ECM assumes BARO value is 92 kPa.

The MAP sensor output signal voltage is a DC voltage that varies with manifold absolute pressure. 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 low MAP reading indicates low load. Code E31 is designed to set when ECM detects a MAP sensor signal out of high side limit, or also with MAP signal at 4.85 volts or more, and having a value greater than 108 kPa.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) If ECM parameter P.0.2 goes to 14-16 kPa with sensor unplugged, fault is at MAP sensor or sensor connector.

Test Number 2) Check for an open circuit from terminal "A" of sensor connector to ECM terminal A5 (ground). If ground is open, sensor cannot divide reference voltage to make signal voltage vary. The signal voltage is always high.