2002 diamante ls pcm issues
 

been trying to repair brother-in-laws diamante ls with a p0401 code, have checked egr valve, changed egr solenoid, had plenum off and checked
/ cleaned passages( were clear when checked) am using a think diag with my phone to check clear codes..this thing is making me crazy. looked here, online and cant find steps and diagrams to show me how to gain access to the plug-in end of the pcm so as to back probe it to check wiring integrity and sensor input to the pcm. when i first started on this journey it had an O2 sensor code which cleared after changing upstream sensors...now its plagued by the dreaded P0401 insufficient egr flow which is why id like to test the pcm.....any help and advice will be welcomed