Should I Set My Truck's Tune Back to Stock Before an Emissions Test?

[Jackpine]

The short answer is NO! Do not change the tune setting in your truck prior to an emissions test! Ignore any conflicting advice you might find in some other source such as the "Edge Manual" - It's WRONG! (Thanks, shinobi.)

If you live in an area where they do emissions testing, on newer vehicles they simply plug a computer into your OBDII port and check for codes. If you show ANY engine or emissions equipment code, you will fail.

Setting your truck back to stock will set the P1000 drive cycle code. This code stays in place for a long time unless you operate the truck through the driving sequence that resets it - which is a VERY complicated process. It will eventually go away through normal driving, but I saw it last for at least 50 miles on my truck after I set it back to stock once. This code would cause an emissions test failure.

Setting the PCM to an advanced tune such as Towing or Performance always clears this code. If nothing else is wrong with the vehicle it should pass an emissions test without trouble. Simply disconnect the OBD cable at the OBDII port and tuck it up behind the dash so the testers have free access to the port. I did not even remove my Gryphon from the dash.

You can also use the Gryphon to check for any codes BEFORE you take your truck in for testing, which I did. Use the [Diagnostics]->[Retrieve DTCs] menu item. You can also "clear" codes (except for the P1000 code) using the [Clear DTCs] choice, but if there's a mechanical problem, the code will return. When you see a code, it's telling you to fix something.

Note: My inspection report has a box labeled "Malfunction Indicator Light Status" and the entry "Commanded OFF", which has a "Pass/Fail" value and mine was "Pass".

I'm guessing here, but I suspect they could be checking for someone possibly "disabling" the "Wrench Light" or other P-Code status indicator. I don't know that using the "Clear DTCs" option would cause a truck to fail this test, but it might. I think it's not a good idea to "Clear DTCs" just before an emissions test.

- Jack