A persistent, slow air leak that causes a tire to slowly go flat and resulting illumination of the TPMS warning light may be caused by corrosion on the (non-chrome plated) aluminum wheel bead seat on 2000-2011 GM passenger cars and light-duty trucks, 2003-2009 Hummer H2, 2006-2010 Hummer H3 and 2005-2009 Saab 9-7X.
Abrasive elements may intrude between the tire and wheel at the bead seat area. Due to relative motion between the tire and wheel, this motion may cause abrasive particles to wear the wheel surface. As the wear continues, corrosive media from the environment may cause corrosion of the wheel bead seat, resulting in tire pressure loss.
According to GM, this type of air loss can generally be corrected by the following procedure. GM warns not to replace a wheel unless you have evaluated and/or tried to repair the wheel with the following procedure.
NOTE: This repair is no longer advised or applicable for chromed aluminum wheels.
1. Remove the wheel and tire assembly for diagnosis.
2. After a water dunk tank leak test, if you determine the source of the air leak to be around the bead seat of the wheel, dismount the tire to examine the bead seat.
3. Bead seat corrosion is identified by what appears like blistering of the wheel finish, causing a rough or uneven surface. Below is close-up of bead seat corrosion on an aluminum wheel that was sufficient to cause a slow air loss.
4. If corrosion is found on the wheel bead seat, measure the affected area. For vehicles with 20,000 miles or less, the total allowable combined linear area of repairable corrosion is 4.00 inches (100mm) or less. If the damage area is larger, the wheel should be replaced. For vehicles that have exceeded 20,000 miles, the total allowable area is 8.00 inches (200mm) or less. If greater, the wheel should be replaced.
5. In order to correct the wheel leak, use a clean-up (fine cut) sanding disc or biscuit to remove the corrosion and any flaking paint. You should remove the corrosion back far enough until you reach material that is stable and firmly bonded to the wheel. Try to taper the edge of any flaking paint as best as you can in order to avoid sharp edges that may increase the chance of a leak reoccurring. Remove only the material required to eliminate the corrosion from the bead surface. Do not remove excess amounts of material. Always keep the sealing surface as smooth and level as possible.
NOTE: Corrosion that extends up the lip of the wheel, where after the clean-up process it would be visible with the tire mounted, is only acceptable on the inboard flange.
6. Once the corrosion has been eliminated, coat the repair area with a commercially available tire sealant such as Patch Brand Bead Sealant or equivalent. Commercially available bead sealants are black rubber-like coatings that will permanently fill and seal the resurfaced bead seat. At 70-degreeF, this sealant will set up sufficiently for tire mountiing about 10 minutes.
