Theory Of Operation

The Exhaust Manifold Pressure (EMP) Sensor is sometimes referred to as the 'Exhaust Pressure 1/1 Sensor'. The EMP Sensor is used to measure exhaust gas pressure in the exhaust manifold. The Powertrain Control Module (PCM) provides a 5-Volt supply to the EMP Sensor on the sensor supply circuit. The PCM also provides a ground on the sensor return circuit. The EMP Sensor provides a signal to the PCM on the Exhaust Pressure Signal circuit. At key on, the readings for the Exhaust Manifold pressure, Intake Manifold pressure, and Ambient Air pressure are compared. This fault code occurs if the Exhaust Manifold pressure reading is different from the other two.

During normal engine operation, EGR position and Boost Pressure Sensor readings are used to calculate an estimated exhaust pressure. If the difference between the estimated and the actual value reading from the EMP Sensor is above a calibrated threshold for a calibrated period of time then an error is recorded. The key-on portion of the rationality will light the Malfunction Indicator Lamp (MIL) immediately after the diagnostic runs and fails. The rationality portion has to fail in two consecutive drive cycles for the MIL to become illuminated. If this fault becomes active the PCM will light the MIL immediately. During this time the PCM uses an estimated exhaust manifold pressure. The PCM turns off the MIL when the diagnostic runs and passes in four consecutive drive cycles.