2012 Jeep Wrangler: DIY TPMS Threshold Reset With AEV ProCal
August 28, 2012
Our Jeep's skinny 225/75R16 OE rubber was designed to run at 36 psi, but this pressure is brutally high when applied to the stiffer carcass of our 285/70R17 BFG Mud-Terrain T/A KM2 off-road rubber. The firmer ride of the 3-inch Mopar Fox/Terraflex lift kit isn't helping much, either.
So we dropped the static inflation pressure to 28 psi, a pressure our big BFGoodrich tires can live with because of their much higher load rating: 121/118 versus 103. But 28 psi is far too low for the OE 16-inch tires, so the factory-calibrated TMPS system gets all pissy when we do this. After all, it has no idea we've changed to different tires with more load capacity.
I wish there was some way to tell it, a way to reset the TPMS trigger threshold in the computer.
There is -- for 2007+ JK Wranglers at least -- and it's called an AEV ProCal.
AEV stands for American Expedition Vehicles, and they're the folks that made our Mopar 5-hole wheels. They also make bumpers, a Hemi V8 conversion kit and lots of other outstanding Wrangler products.
But their ProCal gizmo does a lot more than reset the TPMS trigger point. With this device you can tell your Jeep's ECU about your new tires and differential gear ratios so the speedo is accurate and the automatic transmission shift points are correct. You can use it enable or disable DRLs and that 3 blink turn signal feature.
If you get your alignment too far out of whack it can be set to tell you when the steering angle sensor is centered. And it can be set to temporarily raise your engine's idle speed for a few minutes to help out while winching. There are a couple of other features, but you get the idea: if you're going to mod your Jeep you need one.
Best part is it costs $149, which is less than two visits to the dealer to have the speedometer rescaled by a dealer technician. We've already paid the dealer once to adjust the speedometer to our new 33-inch tires to the tune of $85, the one-hour minimun labor charge.
Strangely, that recalibration was lost when I disconnected the battery to install our Superwinch Talon. Jeep operatives tell me that loss of power is not supposed to do that, but in my experience "not supposed to" is small comfort if it happens anyway. Time to take matters into my own hands.
Opening the hardcover novel-sized box is somewhat anticlimactic because all that's inside is an OBD device that's smaller than a pack of cigarettes. And manuals, of course. Gotta have those.
The manual shows how to set the DIP switches found on the ProCal's backside. Setting these switches in the desired position is step one of a ridiculously easy 2-step process.
Here the ProCal is ready to go with the DIP switches all set. I'll give you a moment to look at the chart and figure out what our new trigger point is. Hint: It's about 20% below our desired running pressure. The TPMS standard calls for a trigger point that's no more than 25% below the set pressure, so we're good to go.
If you guessed 23 psi, you're right. Step two involves turning the key past "acc" to "on" (stopping short of actually starting the engine) and then plugging the ProCal into the OBD port. After a second or two the Jeep's horn will honk two times, indicating the message was received and understood by the ECU.
And that's pretty much all there is to it. The TPMS threshold is now reset. At this point it'll take about three minutes of driving for the light on the dash to go out, the time it takes for all five sensors to report in with their latest pressure readings.
Next on the menu for the AEV ProCal: speedometer recalibration. I've grown tired of using an iPhone app as a stand-in.
Dan Edmunds, Director of Vehicle Testing @ 19,503 miles