if they're going off and on, maybe the battery is going out or they're faulty? what year is your truck again?
anyway, if you want to reset them quickly and easily, buy the expensive tool.
if you have 20min to kill and/or are cheap and want to do it the free way, then follow this guide (it includes pictures):
http://www.thenewx.org/forum/showthread.php?t=40601
it usually takes me a couple of times to get it to go into relearn mode, so if doesn't work the first (or second) time, keep trying.
also don't fret if you drive around for more than 5 miles and they still all show ** for pressure. just keep driving until they all come back, they all will eventually (if they're all working properly).
i'm also pasting the info part of that link (not the pics) just in case that other site goes down or something...
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Instructions:
PLEASE FOLLOW STEP 1. You don't have to be precise with the tire pressure measurement but please try your best.
Step 1: Set the tires to the following pressures, they have to be exact (or try your best to reach those psi, I was off a little but I was able to successfully reset the TPMS):
Tire position Tire pressure kPa (kg/cm2, psi)
Front LH 240 (2.4, 36)
Front RH 220 (2.2, 33)
Rear RH 200 (2.0, 30)
Rear LH 180 (1.8, 27)
I also bought this to help with the tire pressure measurement:
Walmart has something that looks similar but I can't vouch for the accuracy. The great thing is that it's cheaper and it costs around $7.
Step 2: Locate the TPMS interface plug. This is a white female plug that is attached to the OBD II wire loom under the dash right about where your left knee would be when sitting in the driver's seat. You may have to cut the tape that is holding the TPMS interface plug to the OBD II wire loom.I found mine 4 inches up and to the left inside the fuse box near your left knee.It is very short versus other vehicles I looked at.
Step 3: Attach a paper clip or wire into the interface plug. ( I attached it through the back since it was easier for me)
I used a skinny paperclip.
I attached it through the back Since it's a lot easier for the paper clip to make contact with the bare wire.
Step 4: Put your key in the ignition and turn it to the last click before the engine starts.Or push the push start button twice. This is the KOEO position (Key On, Engine Off).
Step 5: Tap the end of the paper clip on any exposed ground (metal) 6 times within 10 seconds of turning ignition on.Make sure it is a real ground and not just any metal you find.
I just tapped it to the metal that's holding the OBDII port. Even though it's not grounded as mentioned in the instruction it worked for me. So it should work for you too ;D.
Step 6: If you completed step 5 then the TPMS warning light will start to slowly flash and you have activated the TPMS relearn process. If it flashes and then stays solid after a minute then check your connections, turn the ignition off and start over at step 4.
Step 7: Once you confirm the lights do not stop flashing, step on the brake and start the car. Do not turn the car to OFF position. Start driving >25mph until the light goes out. It could take as long as ten minutes but for me I drove for 1 to 2 miles and it turned off.
Step 8: The light will quickly come back on due to the low tire pressures. Refill your tires to the correct pressure.
My lights turned off for a couple of minutes but when I continued driving it turned back on and stayed solid. This means your halfway done! Just put your tires back to the proper psi and then your good to go. I was surprised at how fast my solid lights turned off after refilling my tires with air and then driving down a couple houses. I've also experienced times where I needed to drive for 15 miles till the lights turned off.
Note:
If your TPMS lights are flashing, it doesn't mean your TPMS sensors are broken. It's just not syncing with the TPMS system. I was driving on the highway and all the sudden it started blinking. It stayed that way for a couple minutes and then turned solid. When I researched lots of people said this is a sign that a TPMS sensor has malfunctioned. But, I managed to connect the TPMS sensors using the TPMS reset procedure.
If your TPMS lights are blinking even after the TPMS reset procedure, most likely your not doing the procedure properly or one or more of your tpms sensors are broken.
The first time I did this reset procedure my lights stayed solid even after filling my tires to the proper psi. I did the TPMS reset procedure again and it worked.
Your spare tire does not have a TPMS sensor unless you installed one.
The TPMS runs on battery and has a rated 7 year life.