Changing the Tire size and gear ratio on a Jeep Wrangler JL should be an easy task. Well as you will soon find out in this article that may not be the case. As you may know we developed a turbo system for the Jeep Wrangler JL and provide assistance to all our customers whether it is a shop or individual. Most recently we came across a concerned shop because they turbocharged a 2020 manual transmission Jeep JL and a day later the Jeep pulled up on a flat bed. The shop who has performed this install is very familiar with our product. As they gathered info from the customer they become puzzled with the info.
Because of our customer service their first call was to our tuning department. With a provided tune file, data log, and screen shot of current codes we were intrigued by what we saw.
When you are in the ultra high performance market you will find most customers and even dealers will automatically assume your product is the cause of their issue. Being in business as long as we have we know the symptoms of a improper install of the map sensor, or more common a vacuum leak. We have had customers drop their Jeeps off to our location because they swear it is a tune issue. 10 out of 10 times so far that is not the case. We have had failed throttle bodies, cut harness (those are fun to find) even improper wastegate installation. I will not even get into some of the funny things we have seen people do. Use a wastegate spring as a hose guard or a turbo blanket over the compressor housing!
Back to the story, as we received this info we asked our dealer to check and verify a few items. Clear current codes and see what comes back. Check Tire size, initialize ABS modules, reset adaptive, etc. After a day or so all codes had not come back except for one which did not illuminate the CEL. This code was P185F Gear Lever Position Not Learned. We have never scene this code come up after installing a turbo system on a JL or Gladiator. So we started doing some researched, contacted some of our engineers at Jeep and HPtuners. Not one of our sources could advise why this code came up but we knew it was the culprit.
After about 2 days of research I came across an article that FCA put out Click Here to see publication. The Gear Lever all position code will be active if you change the tire size and or gear ratio. This code will trip your ESS and Cruise Control, causing these items not to function.
The fix can be easy and inexpensive, one you can do yourself by following the relearn procedure. the second is more costly unless you have a friend at the dealer! Jeep can program the relearn using their in house software.
In conclusion, if you find yourself unable to set your cruise control or ESS after you change your tire size and or gear ratio in your manual Jeep Wrangler JL! It could just be a simple relearn to get your Jeep back to normal!
for more info and other knowledge check out our blog page HERE.