Component Diagnostic Charts - Throttle Body Fuel Injection

Chart C-1D:

Wiring Diagram For MAP Sensor:

CIRCUIT DESCRIPTION:

The Manifold Absolute Pressure (MAP) sensor measures manifold pressure (vacuum) and sends that signal to the ECM. The ECM uses this information for fuel and spark control.


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

1. This checks MAP sensor output voltage to the ECM. This voltage, without the engine running, represents a barometer reading to the ECM.
2. Applying 34 kPa (10" Hg.) of vacuum to the MAP sensor should cause the voltage to be 1.2 - 2.3 volts less than the voltage at Step 1. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for a leak or a restriction. Be sure that no other vacuum devices are connected to the MAP sensor hose.

DIAGNOSTIC AIDS:

With the ignition "ON" and the engine not running, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. A comparison of this BARO reading, with a known good vehicle with the same sensor, is a good way to check the accuracy of the problem sensor. BARO readings should be similar within +/- 0.4 volts.