Land Rover Repair: 2003 Freelander Land Rover, actron scantool, actron code scanner

Question
My "Service Engine Soon" light is illuminated.  I used an Actron Scantool and got codes 1470 and 1472. I replaced both varible intake butterfly valves and cleared the fault.  Then the "Service Engine Soon" light illuminated again.  I replaced the sparkplugs with NGK Iriduim spark plugs and change the oil and filter (Mobile 1 0W30). The Actron code scanner says P0172 and P0175.  What do you think is the problem?  Does Land Rovers Test Book give the same codes as an OBD II scanner?  My thought is to replace both Ho2 sensors.  What do you think is the problem?

Answer
I can't tell what the problem is, given your descritpion.  It sounds like you replace some parts to address a code, and a new code appears.  Are you causing the new codes with errors in workmanship?  Are you making wrong choices in the first place?  I can't tell.

Fault codes are not a one-stop source of part-changing data.  The T4 system would show live data, and illustrate the out-of-range parameters so that a technician can make a reasoned judgement as to what's really going on.  That's not possible with codes alone.

In addition, testers like the T4 allow us to activate or deactivate various systems to perform diagnostic tests.  Without tools like that, you are really just guessing and hoping to get lucky.