Using a scan tool, watch the map sensor value
with the key on, engine off. Compare the Barometric reading with the MAP reading.
They should be roughly equal. The voltage for the MAP sensor should read approx.
4.5 volts. Now start the engine and look for a significant drop in the MAP sensor
voltage indicating the MAP sensor is working.
If the MAP reading doesn't change perform the following:
- With the Key on, engine off, disconnect the vacuum hose from the MAP sensor.
Using a vacuum pump, pull 20 in. of vacuum on the MAP sensor. Does the voltage
drop? It should. If it doesn't inspect the MAP sensor vacuum port and vacuum
hose to manifold for a restriction of some kind. Repair or replace as necessary.
- If there are no restrictions, and the value doesn't change with vacuum,
then perform the following: with the Key on and engine off and the MAP sensor
unplugged, check for 5 Volts at the reference wire to the MAP sensor connector
with a Digital Voltmeter. If there is none, check for reference voltage at
the PCM connector. If the reference voltage is present at the PCM connector
but not the MAP connector, check for open or short in the reference wire between
MAP and PCM and retest.
- If reference voltage is present, then check for existing ground at the MAP
sensor connector. If it isn't present then repair open/short in the ground
circuit.
- If ground is present, then replace MAP sensor.
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