ive owned this MS 4x4 XLS 3.0 since new. In Kalifornia we test every 2 years as I recall. I had my recent test yesterday and passed all emissions,but since the tech found a light on my instrument panel he had to fail the test. The fail is automatic if a "check engine or service check" amber light is displayed.So, he ran the codes and came up with a P1400 which refers to the Manifold pressure Differential sensor. BTW for those of you that are interested for whatever reason,the cost to this point is $45 for the smog test and $40 for pulling the code. replacement of the sensor will be $345.
Im suprised that after 218K & 14 years no other smog related part or emissions have failed.
Im curious,has anyone ,that may have a little OCD for this thing , kept track of any patterns or sequences in the eventual and progressive breakdown of the smog equipment?

2. what is the purpose of this sensor that failed?

 

Manifold Differential Pressure sensor should be about $100. Order the part and replace it yourself = save $200 for other things. It is usually located on the top of the manifold and has an electrical connector and 2 screws to bolt it down. Very easy replacement.