Powertrain Controls - ECM/PCM

DTC 31 EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum):

CIRCUIT DESCRIPTION
A Manifold Absolute Pressure (MAP) sensor is used to monitor the amount of vacuum in the Exhaust Gas Recirculation (EGR) circuit. It senses the actual vacuum in the EGR vacuum line and sends a signal back to the Powertrain Control Module (PCM). This signal is used to control EGR duty cycle calculated by the PCM.

DIAGNOSTIC TROUBLE CODE (DTC) 31 WILL SET WHEN
EGR pressure is less than 15 kPa for 2 seconds.

ACTION TAKEN (PCM will default to)
The PCM will shut down the EGR system.

DTC 31 WILL CLEAR WHEN
The fault condition(s) no longer exist, and the ignition switch is cycled "OFF" the "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step determines if DTC 31 is a hard failure or an intermittent condition.
2. Jumpering hamess terminals "B" to "C" (5 volts to signal circuit) will determine if the sensor is at fault, or if there is a problem with the PCM or wiring.
3. The Tech 1 scan tool may not display 5 volts. The important thing is that the PCM recognized the voltage as more than 4 volts, indicating that the PCM and CKT 433 are OK.

DIAGNOSTIC AIDS
With the ignition "ON" and the engine stopped, the EGR pressure is equal to atmospheric pressure with the signal voltage being high. The information is used by the PCM as an indication of vehicle altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be the same ± 0.4 volt.
An intermittent open in CKT 433 or CKT 416 will result in a DTC 31.