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.

The ECM turns on SERVICE SOON light.
ECM sets BARO at 92 kPa and looks up a substitute MAP sensor value from a table of substitute MAP versus RPM, when throttle switch is closed.

The MAP sensor output voltage is a DC voltage that varies with MAP. As MAP decreases, voltage on circuit No. 432 decreases (low engine load and high engine vacuum). As MAP increases, voltage on circuit No. 432 increases (high engine load and low engine vacuum).

The ECM uses MAP sensor reading as an indicator of engine load. Low MAP readings mean low engine load, and high MAP readings mean high engine load. Code E34 is designed to set when ECM detects a MAP sensor signal that is much too high for closed throttle test conditions. Code E34 usually indicates there is fault in vacuum supply to MAP sensor.

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

Test Number 1) MAP at idle should be 30-50 kPa, depending on engine load. BARO should be 85-105 kPa depending upon altitude.

Test Number 2) Check for vacuum at MAP sensor hose with vacuum gauge. At idle, typical vacuum readings are 14-20 in. Hg depending on engine load.

Test Number 3) Check faulty MAP sensor or MAP circuitry.

Test Number 4) Check for sensor ground open from sensor to ECM.

Test Number 5) Check for short to voltage on sensor signal circuit No. 432.

Test Number 6) Fault is most likely at ECM connector or ECM. Before ECM is replaced, perform CHART C-1: ECM REPLACEMENT CHECK .