Test Notes

NOTE: You should enter this pinpoint test only when you have been directed here from diagnostic routines, or Pinpoint Test S.

To prevent the replacement of good components, be aware that the following non-EEC areas may be at fault:
- Unusually high/low barometric pressure
- Kinked or obstructed vacuum lines
- Base engine concerns (valves, vacuum leaks, timing, Exhaust Gas Recirculation (EGR) valve, etc.)

This pinpoint test is intended to diagnose only the following:
- MAP/BARO sensor
- Harness circuits: VREF, MAP/BARO SIG, and SIG RTN
- MAP vacuum line
- Powertrain Control Module (PCM)

OPERATION
The Manifold Absolute Pressure (MAP) sensor operates as a piezoelectric (pressure-sensing) disc. However, rather than generating a voltage, it outputs a frequency change. The sensor changes frequency relative to intake manifold vacuum. The sensor frequency increases as vacuum decreases. The MAP sensor allows the PCM to determine the engine load. The signal affects air/fuel ratio, ignition timing, EGR flow and altitude compensation.

The BARO sensor is used to sense the changes in barometric pressure, allowing the PCM to compensate for the altitude at which the vehicle is operating. Its signal affects air/fuel ratio, spark and EGR.