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July 2015 31 with proper stoichiometric mea- sures of 14.7 parts air to 1 part fuel. You will read that the normal operating temperature of a catalyst can run between 1,200-1,600°, but it can start degrading around 2,000°. This higher 2,000° tempera- ture is caused by excessive emis- sions and, if not dealt with soon, can cause either a clustering of the precious-metal load or substrate breakdown. The clustering is when the load shifts to the back of the brick and therefore the duration of catalyst activity has lessened. There is less time in the brick to do the reduction and oxidation is an easier way to look at it. Remember that vermiculite blanket we spoke of in the begin- ning of our article? How important is it in the reduction of emissions? Well, the vermiculite blanket does not do any of the emission reduc- tion, but it plays a big part in the life of the catalyst. This blanket protects and centers the brick in its stainless-steel case or shell. There should be a break in process with a new catalyst. That vermiculite blanket needs moisture to expand and tighten the brick in place (Figure 2). Hydrocarbons when burned do create some moisture, or water, in the process and, with heat, that water turns to steam. That steam causes the blanket to expand and lock the brick in place. The expansion only needs to hap- pen one time and the blanket will remain expanded during the life of the catalyst. Have you ever heard a fairly new catalyst rattle? Well, what has happened is that catalyst has not had a proper break in. If a vehicle has left your shop and the cus- tomer only drives short trips, you will find them back at your doorstep for a warranty catalyst. Train your customers to get out and drive that vehicle on a long trip for the first day, for two good reasons. The first reason is to clear out any of the residue that remains on the new cata- lyst so it can be fully acti- vated for smog, and to allow time for the blanket to lock in the brick (Figure 3). Short trips will allow the exhaust pressure to push the blanket out of the shell and through the tailpipe. The only good that blanket would do then is provide a home- less cockroach a warm night's sleep! As I mentioned early on in this article, knowledge is power. A lit- tle knowledge is dangerous, and a lot of knowledge is sometimes overwhelming, so I hope I met it somewhere in the middle. ■ Ed Hanson is a veteran exhaust-system technician and former shop owner. You can contact him at ed.hanson.email@gmail.com GM Wheel-Speed Sensor Diagnosis and Service An intermittent click, grind noise or ABS pump motor noises may be heard inside a number of 2007-14 GM vehi- cles at parking lot speeds; and the ABS, Service Traction Control System, and/or Service StabiliTrak warning lamps may be on. DTCs C0035 (left-front corner), C0040 (right-front corner), C0045 (left- rear corner) or C0050 (right-rear cor- ner) with symptom bytes 18, 5A, 0F may be set. The conditions may be caused by ferrous metallic debris stuck to the wheel speed sensor magnetic encoder ring, which is part of the inboard bear- ing hub assembly. (This does not apply to capped wheel bearings.) Vehicles equipped with electric power steering may have a heavier steering feel at low speed and DTC U0415 may be set in the power-steering control module. This is a normal default action with the loss of a wheel-speed sensor signal. Cleaning the magnetic encoder ring will repair the condition in most instances, but DO NOT use a magnetic tool to remove the debris, because it can damage the encoder. Use a dry nylon soft-bristle brush. If debris remains, wash the encoder ring using a mild detergent soap. Removal of the bearing/hub assembly may be required. Circle No. 31 on Reader Card A dirty wheel-speed sensor can trigger codes in a number of 2007-14 GM vehicles. Simple cleaning can solve the problem.