Chart C2, Map Sensor Check
A Manifold Absolute Pressure (MAP) sensor is used to monitor vacuum in the EGR vacuum circuit. It also sends the ECM a barometric pressure (altitude) signal when the ignition switch is on without the engine running or with the engine running when EGR is not in operation. This signal allows the ECM to control altitude related injection pump timing and metering valve travel at wide open throttle. The barometric signal is also used by the ECM along with absolute EGR control pressure, coolant temperature, metering valve position, TCC state, vehicle MPH, and engine RPM to determine and control EGR Pulse Width Modulated (PWM) duty cycle.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Checks for reference voltage at MAP sensor harness. Normal voltage at terminal "C" of MAP harness should be about 5 volts.
- Checks for an open ground in the MAP circuit to ECM. Normal voltage is about 5 volts with a good ground.
- Checks for proper circuit from the MAP signal wire to ECM terminal "P". Incorrect voltage is an open or grounded wire, or faulty MAP sensor. Normal voltage is shown on table at bottom of chart.