Oxygen sensor mix-ups? Oh my!
Q. I have a 2002 Oldsmobile Silhouette. I had the oxygen sensor replaced by the dealer after the "service engine soon" light came on. The very next day the car would not start for my wife. She called me at work and explained that the engine would not turn over and the "security" light was on. I could hear the door alarm dinging in the background.
I asked if the radio was playing and she said "yes," which led me to think it was not a battery problem. I then recalled that the GM key has a chip in it for security purposes.
I told her to go into the house and get my key to her car. She did, and the vehicle started. I then told her to retry her key, and this time it started and has been working since.
The dealer says the work done to replace the oxygen sensor would not have affected the security module or the key.
Any explanation?
A. I don't think it's at all related to the oxygen sensor or anything the dealer did. I suspect her key was simply having a bad day.
More seriously, there's a transponder in the key that the anti theft system in the car needs to interrogate before the car will start. If those keys weren't so expensive, I'd tell you to replace it.
Q. I've had a 1998
Two months later, while going down a road, the van shifted into first gear and then got stuck there. We parked the vehicle while waiting for a repair. It fixed itself. The mechanic could not find anything wrong.
Six months later the tranny has started doing it again -- after a 15-minute drive, it shifts into first gear and stays there. (At 70 miles per hour that engine really roars!) After the van cools down, it starts normally again.
Of course the transmission shop says this problem is not its fault. A co-worker suggested that they check the throttle sensor.
Any ideas?
A. It's probably not going into first gear, but second gear, which is the tranny's limp-home mode. This happens when the controller has decided it is no longer capable of making correct decisions because a sensor is returning data that's too far out of bounds.
To diagnose the problem, your mechanic should hook up a scan tool to the truck so that it can record the malfunction as it happens.
Q. My 2005 Chrysler 300C has a 5.7-liter V-8 Hemi engine and 16 spark plugs. Since it's a Hemi, with the spark plugs sticking out of the top of the valve cover, I figured I could easily get to all the plugs to change them. But when I removed the plastic cover over the top of the engine, I found that only one plug had a direct wire. Some kind of weird gizmo is over the other plugs.
What is that thing? Should I let the dealer charge me an arm and leg to change the plugs? Or is this something a weekend mechanic can do?
A. That gadget on the other plugs is an ignition coil. No problem.
Use a sparing amount of grease on the boots. Be sure to dress the ignition wires exactly as they were installed at the factory.
Q. I have a 1999 Buick Regal with a console that separates the driver and the front-seat passenger. I also have two children, who have managed to spill a lot of stuff in the car over the years.
The latest spill was hot chocolate. It sloshed right over the console, particularly on the area where the shift is located. I would like to remove this console, clean the area and replace it. How do I do this? I cannot find any screws to remove.
A. There are two bolts under the rubber mat in the storage compartment, two under the trim surrounding the shifter, and two at the front of the console on the side, one each side. You will need to put the shifter into "low" to get the trim off, so block the wheels or set the handbrake.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com. 
