Q I have a 2007 GMC Envoy. In the winter the "service StabiliTrak" light comes up on the dash. In summer it does not come up often, maybe once or twice all summer, but in winter it comes on once or twice a week. To reset the light you have to turn off the ignition and restart the Envoy. I had a scan done to check for codes, but there weren't any.

The problem occurs when the vehicle rocks coming out of a driveway or when making a sharp turn to the left while backing up. Can you shed some light on this problem?

A You may be in luck. My Alldata automotive database pulled up service bulletin 08-05-25-005, dated October 2008, that describes a dynamic condition similar to what you're experiencing that can trigger the light.

This may be caused by "a software anomaly within the electronic brake control module (EBCM) that allowed the yaw offset to be falsely learned." It means the system has learned to recognize a sudden change in the "yaw" axis as a condition that requires engaging the stability control system.

(Yaw is the change in the car's front-to-back axis relative to the direction of travel.)

In this case, the system thinks the vehicle is beginning to spin or slide and tries to stabilize the vehicle.

The bulletin calls for the dealer to reprogram the module with updated software. If the vehicle is still covered by warranty, so would this update.

Q BMW says it doesn't recommend rotating tires on my 2007 530xi, even though they are all the same size. I followed its recommendations, and when I had to get new tires, I wound up with worn-out tires in the rear and two front tires that had about 5,000 miles left on them.

I also have a 2001 Audi Allroad that has four tires the same size, which I rotate. As a result, I wind up getting a uniform wear rate and possibly six more months of wear.

What do you think about the difference in tire rotation practice between Audi and BMW?

A When you rotate the Audi's tires, do you have to reset or reprogram a tire pressure monitoring system? It was an option on your Audi but is now standard equipment. If you don't, that may explain most of the "don't rotate tires" advice on the BMW. If you were to rotate the tires on the BMW, you would have to reset the tire pressure monitoring system to recognize the change in location for each tire pressure sensor. Check your owner's manual for instructions.

Q I'm trying to locate the fuel pressure regulator to fix a hard-starting 1998 Chevy C2500 pickup truck with a 5.7-liter Vortec engine. The engine starts quickly when cold but cranks a while to restart when hot. It occasionally backfires through the intake manifold. The fuel pump was replaced and an induction cleaning done at 75,700 miles. Current mileage is 93,500.

Am I chasing after the wrong solution?

A A simple fuel-pressure leakdown test would identify a leaking fuel pressure regulator or CSFI (central sequential fuel injection) injector. Fuel pressure should be 60 to 66 pounds per square inch, and it should hold that without dropping rapidly once the key is turned off and the fuel pump stops running.

The regulator and "spider" CSFI assembly are under the upper intake manifold, which must be removed to gain access. If there's no problem with fuel pressure, a compression or cylinder balance test might identify a leaking intake valve.