2002 Honda Accord 3.0L V6 - Persistent P0401 and P0705/P0706 Codes After EGR Replacement and Intake Cleaning
I have a 2002 Honda Accord with a 3.0L V6 engine. I recently replaced the EGR valve, removed the intake manifold, and thoroughly cleaned all components twice. Despite these efforts, the vehicle continues to show P0401 (EGR System Efficiency Below Threshold) and additional codes P0705 and P0706 (Transmission Control Module Issues). What could be causing this? Are there any other potential causes or diagnostic steps I should consider?
Are there any other diagnostic trouble codes present? Try observing the MAP sensor readings while commanding EGR flow using an OBD2 scanner. To test EGR functionality, temporarily connect terminal 4 to 12V and terminal 6 to ground—this should open the EGR valve, causing the engine to stall. If the engine stalls or shows inconsistent behavior, it may indicate a faulty EGR system or sensor. Consider checking for other underlying issues or a malfunctioning MAP sensor.