[JFP in PA]

Originally Posted by yelcab1

That is the problem. The lower temperature thermostat is telling the CPU to enrich the mixture in order to warm the engine up some more. Since it can never do that with the new lower thermostat, it will not pass … smog.

Options are to …

1. Reprogram the CPU, Hard
2. Replace with stock thermostat to bring the engine operating temperature up, easier
3. Give the car a tune up while you are at it. Change the air filter, spark plugs, oil, and drive it aggressively for a few days then take it to test again.

Sorry, but that is utter nonsense. We have a couple hundred customers running 160F thermostats, and NONE of them have ANY issues. The factory DME tune has more than enough flexibility to adjust for the coolant temp change.