Start with the t-stat, its cheapest and easiest.

 

Hey guys, hijack here, but I can't shake my 0125 code and subsequently can't pass emissions. Replaced thermostat and temp sensor, scantool reads between 150 and 175 when warmed up. Heat is hot and engine seems hot but reading is low. Any suggestions? 96 disco, 5sp.

 

I dont know what the 0125 code means, but your truck is running WAY to cold, which will make it run to rich, which will increase emissions.

 

Any suggestions?

 

Change the t-stat.