A My ALLDATA automotive database pulled up GM bulletin #05-02-32-008D dated July of this year that identifies the 4-bolt 680 steering gearbox as an upgrade replacement for the original 3-bolt 670 gearbox.
But before replacing the steering gearbox, make sure the serpentine belt is not slipping, the power steering system is full of the proper fluid, and no air is trapped in the system. The easiest way to bleed air from the system is to raise the front end safely with jack stands under the lower control arms, start the engine and gently cycle the steering from lock to lock several times, holding it at full lock only momentarily in each direction. Adding 2 ounces of Sea Foam Trans Tune to the power steering reservoir can help clean and de-moisturize the fluid and the steering gearbox.
If you do experience a loss or reduction of power steering, try increasing engine speed. If slightly higher rpm restores power steering performance, you could try a relatively inexpensive complete flush and refill of the power steering system to remove any debris and contaminants. If you still have a problem, GM suggests installing a special hydraulic test device in the pressure hose to determine if there is adequate hydraulic pressure and/or any restrictions in the system or steering gearbox.
Q I have a 2007 Grand Caravan SXT and the right rear taillight has quit working. The brake, turn and backup lights still work. I have replaced bulbs, checked fuses, swapped left side taillight assemblies with right side to confirm it is not an assembly problem. My conclusion is it must be a broken wire between the front and rear of the car.
A Or a bad connection somewhere. First, check 15-amp fuse No. 2 in the Integrated Power Module fuse block. It protects the right side circuit in the parking lamp relay. If it's good, check for a solid ground connection from the terminal in the lamp socket to ground -- there should be no resistance. Then check for voltage from the positive terminal in the socket to ground. Assuming no voltage or ground, check the 6-pin connector located behind the right rear taillight assembly in the quarter panel.
Q When I am driving my friend's 2004 Buick Century at night and switch from low to high beams, the lights go completely off. A quick switch of the lever gets them back on. Needless to say, on dark country roads with oncoming traffic, this is scary for us. Your thoughts on this problem would be appreciated.
A The likely culprit is the turn signal/multifunction switch or harnesses in the steering column. Whenever the steering wheel is tilted up or down, the harnesses from this switch are flexed. Over time an internal wire fracture may occur that creates intermittent operation of this switch. Since the switch is over $500, check the connectors for this harness under the dash and at the fuse box first.
Speaking of multifunction switches, this from Ron Christianson in regard to last week's "no start" Cadillac. "I had a similar experience with the security system with a new 1989 Cadillac Eldorado. The problem turned out to be a break in the wiring harness in the steering column. When the steering wheel tilt is moved up and down it flexed the printed wiring cable until that circuit broke."
Nice timing, Ron. Thanks!