Exhaust Gas RECIRCULATION (EGR) System

The Powertrain Control Module (PCM) monitors the Exhaust Gas Recirculation (EGR) valve and system for several failure modes.

EGR Valve (DC Motor) 

The PCM performs electrical diagnostics on the EGR valve and circuits. If the PCM detects that the current draw or Pulse Width Modulation (PWM) to the EGR valve is too high or low for a calibrated period, the PCM determines that the EGR valve motor or circuitry is faulted and not operating properly.

• The PCM can detect a circuit high or circuit low fault during operation of the component, whereas open circuit detection can only occur when the component is not being commanded ON. If an open occurs in the component or circuits during the operation, the PCM will normally detect the failure during the performance diagnostic for the system that the component is being used to control.
• The EGR valve control circuits can be driven high or low depending on whether the EGR valve is being opened or closed.
• The PCM monitors the EGR control circuits for excessive current draw in both directions. The following are the possible failure modes of the EGR control circuits:
  • A short to ground fault in the EGR valve (+) control circuit will set the P1E27 or P01E28 DTC, depending on which direction the EGR valve is being driven when the fault occurs.
  • A short to ground fault in the EGR valve (-) control circuit will set the P0489 or P0490 DTC, depending on which direction the EGR valve is being driven when the fault occurs.
  • An open circuit or short to voltage fault in either EGR valve control circuit will set the P0403 DTC.

EGR Position Sensor 

The PCM performs the circuit low and high fault diagnostics on the EGR position sensor signal. The sensor is determined to be irrational if the difference between the actual valve position and commanded valve position is more than a calibrated threshold when the EGR valve is commanded open.

• The PCM learns the EGR valve open and closed positions once per drive cycle. In the case of an EGR valve replacement, the "EGR VALVE REPLACED" routine  should be performed using the diagnostic scan tool.
• The PCM monitors the EGR position sensor during the operation to determine if the EGR valve is in the correct commanded position. The EGR valve is monitored for over-shoot conditions and offset from the learned open and closed positions.

EGR Temperature Sensor 

The PCM performs the circuit low and high fault diagnostics on the EGR temperature sensor signal. The sensor is checked for rationality after a cold soak. At the next key ON after a cold soak, the EGR temperature sensor signal is compared to the Engine Coolant Temperature (ECT) sensor signal and Ambient Air Temperature (AAT) sensor signal. If the difference between the EGR temperature sensor signal and the other signals is more than a calibrated threshold, the EGR temperature sensor rationality diagnostic fails. If there are no EGR temperature sensor faults present, the PCM uses the feedback from the sensor to monitor the efficiency of the EGR cooler during operation.