Circuit Description

PCM will test EGR system during deceleration by momentarily commanding EGR valve to open. The pressure in intake manifold increases when EGR valve is open. PCM monitors MAP sensor signal during EGR system diagnostic in order to determine amount of EGR flow. PCM calculates an error based on the difference between actual MAP increase and a predetermined value, and records the error and adjusts an internal fail counter towards the fail threshold if error is too great.

PCM sets DTC when the fail counter exceeds the fail threshold. The number of test samples required to exceed the fail threshold varies according to magnitude of detected flow errors.

PCM allows only one EGR flow test sample to be taken during an ignition cycle. PCM will allow 12 test samples during the first ignition cycle in order to aid in verifying a repair after battery is disconnected or after performing CLEAR INFO on scan tool.

Conditions required to set DTC are:

• DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0404, P0500, P0502, P0503, P0560, P0562 or P0563 are not set.
• Ignition voltage is 11.7-16.0 volts.
• BARO greater than 70 kPa.
• ECT is 140-243°F (60-117°C).
• IAT less than 140°F (65°C).
• Engine speed at 800-2000 RPM.
• Engine vacuum (BARO minus MAP) 9-12 psi (60-83 kPa).
• IAC position steady.
• Vehicle speed at 27-70 MPH.
• Change in VSS is less than 4 MPH.
• Change in MAP is less than 0.5 kPa.
• A/C clutch status is steady.
• Change in MAP is less than a predetermined value the EGR flow test.
• Conditions present for 2 seconds.