Permanent DTC

[Bonnewagon]

I never heard of this before. My daughter's 2012 Jeep 3.7 Liberty had a #2 cylinder misfire code. I bought a new spark plug and swapped it in just to get rid of the code. I will do a total tune up when winter quits. But when I went to clear the code the MIL went out but a "Permanent DTC" was left behind. You can't erase it by normal means. I snooped and found it is a way to keep people and shops from clearing the codes just long enough to pass inspection and not fix the problem. It was introduced in 2009 and in 2010 it was universal. So how do you get rid of it? By doing a dedicated procedure that varies by manufacturer. This one is the most common and it is called the Universal Trip Drive Pattern. Here is the proceedure:
[Typically, this Universal Trip Drive Pattern starts off by clearing all the DTCs so that only the Permanent DTC remains (always refer to service information for applicable information and procedures).
Then turn the ignition ON, start the vehicle and let it idle for at least 30 seconds. Then, without cycling the key, drive the vehicle for at least five minutes at more than 40 km/h. Then (again without cycling the key) let the vehicle idle for at least 30 seconds before shutting it OFF. The whole drive cycle must take at least 10 minutes. After performing a Universal Trip Drive Pattern, the computer clears the code, since it’s “seen” that the problem is fixed and not reoccurring.]

 

[Doug Chahoy]

Seems like they’re intension is Don’t Touch Crap. That whole procedure is a joke. And I bitched about what you have to do to change a battery now days. All that BS just because 1 spark plug was bad. That’s why when we buy a new vehicle, I make sure the b to b warranty is as long as the payments. I don’t touch this new stuff.

 

[fleming442]

The head is cracked.

 

[Bonnewagon]

I look at it this way- if I ignored the worn out spark plug then it would continue to let un-burned fuel pass out of the engine. That gets to the Cat and over-heats it. It melts and sets an even worse code. The Cat costs $2000 at the stealership. So if it takes a bit of effort to clear the code and to be sure it is really fixed I am willing to go along with that. The drive cycle is there so a shop can determine if the fix worked without waiting for the owner to drive for weeks and see if the code comes back. But why is the information so hard to find? That pisses me off. Just as why did whoever-owns-Jeep-these-days put the cheapest possible spark plugs in the engine? They are only good for 30k and this Liberty has 80k on it. So mileage was probably bad for a long time. They didn't even use platinum plugs which are as cheap as the cheapolas these days. I use Iridium plugs in all my "new" vehicles just because Iridium will most likely outlast me.