Circuit Description

The barometric pressure (BARO) sensor measures the pressure of the atmosphere. This pressure is affected by altitude and weather conditions. A diaphragm within the BARO sensor is displaced by the pressure changes that occur from varying altitudes and weather conditions. The sensor translates this diaphragm action into the voltage signal input that is used by the powertrain control module (PCM) for diagnostics and emissions control.

The supercharger inlet pressure (SCIP) sensor measures both the atmospheric pressure and the vacuum that exists under different operating conditions in the supercharger intake plenum. The plenum volume between the throttle body (TB) and the supercharger is where this sensor is located, and for the purpose of this diagnostic, this area is considered to be the intake manifold. The diaphragm within the SCIP sensor functions in the same manner as the BARO sensor. The sensors are not interchangeable. The actual measurement from the SCIP sensor is used by the PCM to calculate the difference continuously between BARO and SCIP. The calculated difference is displayed as the SC Inlet Pressure parameter.

The purpose of this diagnostic is to analyze the correlation between the BARO sensor, and the SCIP sensor. This is accomplished by comparing the difference between BARO and SCIP at key ON, engine OFF (KOEO), at closed throttle idle conditions, and at wide open throttle update events. At KOEO the difference between BARO and SCIP is represented on the scan tool by the SC Inlet Pressure parameter as a value that should be very close to zero. A negative SC Inlet Pressure parameter means that the BARO sensor value is less than the SCIP value. A positive SC Inlet Pressure parameter represents a BARO sensor value that is more than the SCIP value.

At idle the SC Inlet Pressure parameter represents the calculated difference between BARO and the reduced pressure that is present in the supercharger intake plenum as a positive value. At wide open throttle the SC Inlet Pressure parameter represents the calculated difference between BARO and the increased pressure that is present in the supercharger intake plenum, and should be very close to zero.

Both sensors have the following types of circuits:

• A PCM supplied and regulated 5-volt reference circuit
• A PCM supplied ground for the low reference circuit
• A sensor signal circuit that supplies a voltage input to the PCM

Changes in BARO due to weather are relatively small, while changes due to altitude are significant. Pressure can range from 56 kPa at an altitude of 4267 meters (14,000 feet), to 104 kPa at or below sea level.

If the PCM detects that the BARO sensor signal and the SCIP sensor signal are not within a calibrated range of each other, whether that value is negative or positive, DTC P0069 sets.