Getting My Wires Crossed
Q: I have a 2006 GMC Sierra SLE. While plugging in the trailer lights, I crossed the plug and blew the fuse (the white and brown wires). I have searched my owner's manual to find the location of this fuse without results. It's labeled in such a way that I can't understand which one of the fuse boxes or fuses control the trailer taillights. Where can I find this fuse?
A: I take it you crossed the wires coming from the trailer to the seven-way connector at the truck's hitch assembly, and you've since wired the trailer harness correctly. The white wire is a ground, simple enough. The brown wire supplies 12 volts to the trailer parking lights. As you know, connecting power to a ground without a load (light bulb, motor, etc) in between results in a blown fuse, or a fire, one of the two. Open the hood. The underhood fuse block should be mounted on the left side, on top of the wheelwell. Remove the fuse-block cover. There should be a label inside the cover designating the names and locations of all the components in the block. Look for the fuse marked "TRL PARK" on the left side of the block. My service information shows a discrepancy between the wiring diagram and the fuse-block label. One shows TRL PARK being a 10-amp fuse, and the other a 15 amp, so it could be either one. Pull it out; if it looks burned, replace it with the same amperage fuse. In the future you may want to invest in a 12-volt test light. It's a good way to find a burned-out fuse quickly, even if you're not sure where to look. Just turn on all the applicable circuits--in this case the "Park" lights. Attach the alligator-clip end of the test light to a good ground (anything metallic that's bolted to the chassis). Then touch the pointy end of the test light to each side of every fuse you can find. If the fuse is good, both sides will light up the test light. If the fuse is bad, only one side will light it, because the burned-through element within the fuse is cutting off the power source.
A Door that's not a Jar
Q: With all the doors securely closed and even locked manually on my 2002 Expedition, the "door ajar" indicator still appears. I was wondering if I could disable this: I currently have to pull the fuse out every time I leave the truck, or the runningboard lights and the overhead light will stay on and drain my battery. Also, normally after reaching 15 mph the lights shut off, yet once I turn the truck off they come back on and they stay on.
A: Not as simple a circuit as in the old days, when almost every manufacturer used pushbutton door-ajar switches mounted in the A- and B-pillars. The switches in those circuits simply provided ground paths for the interior lights and the door-ajar indicator lamp in the dash, if equipped. Your Expedition has ajar switches mounted in all four doors, plus the rear hatch and the rear hatch glass. These switches still provide a ground path, but not to the lights. Instead, they're wired to what we call a generic control module. The GCM observes the input data from the door-ajar switches and then decides whether to turn on the door-ajar indicator, the courtesy lights, and/or illuminate the runningboards. But these switches are subject to the wear and tear from opening and closing the doors. Therefore they do commonly fail, and replacing some of these switches will require a teardown of the door in question. With the ignition on and everything closed, run around and push, pull, and jiggle every door, hatch, and glass while keeping a close eye on the door-ajar indicator lamp. If you see it go off or flicker, while disturbing one door in particular, the ajar switch at that location is most likely the problem. Otherwise it's going to require a technician to track down the cause, beginning with the evaluation of inputs and outputs at the GCM. And I wouldn't suggest bypassing anything; it may produce problems elsewhere.
Where's First Gear?
Q: I recently purchased a 2007 2WD extended-cab Z71 Silverado with the 4.8-liter V-8. Why didn't anyone ever mention that the truck limits first-gear activity? From a dead stop, I bet I'd lose a 60-foot race to a lawnmower--when you floor the truck from a stop, it either bogs or the computer limits the power so much that you barely move. I don't have traction control so I find this odd. I took it to the dealer and he said it drove like any other 4.8-liter Silverado. Is this a program just for these new trucks? My dad has a 2007 Silverado Classic with the 4.3-liter V-6 automatic and it gets up and goes, even leaving an occasional black mark.
A: Your truck's low-end performance may be as good as it gets. To make sure, the next time you put the pedal to the floor, first put the transmission in manual first gear. See if you notice any advantage as compared with starting in Drive. Then wind it out (pre-redline) and upshift manually to second gear. If it bangs into second as it should, the transmission is functioning correctly. If it doesn't, the transmission may be starting in second gear as opposed to first, resulting in sluglike acceleration. A bad torque converter can produce similar symptoms, but that happens more often on high-mileage or abused transmissions. If there were a significant performance issue with the engine itself, chances are the "service engine soon" indicator would be lit, and the boys at the service department would have noticed it. Here are a few factors that may explain performance variations between your new Silverado and Dad's Classic. It depends on the exact model and options on each truck, but in general, the new Silverado is a little heavier. The 4.8-liter puts out 100 horsepower more than the 4.3, but only offers 45 more pound-feet crucial low-end torque. Also, Dad may have gotten the optional 3.73:1 axle ratio, while your truck has the standard 3.23:1 highway gears. Plus mounting taller tires on any vehicle will lessen your jump from a start. Worst case, there are aftermarket intake, exhaust, and electronic calibration products that can improve your standings.