Q. My 2002 Chevy Trail Blazer, which I’ve now driven for 55,000 miles, is experiencing a problem. When the “service engine” light comes on, the “engine low power” light illuminates as well. This has happened a few times. The throttle body has been replaced, and then the accelerator pedal with electronics was replaced, as well as the spark plugs. There were no concerns reported on the emissions test. When this problem occurs, I turn the engine off and restart it again. The “service engine” and “low engine power” lights then go out for an undetermined amount of time, and then the problem reoccurs. What do you think?

A. Some General Motors vehicles can have a problem with the engine cooling fan. When the fan is a problem, the technician may find either diagnostic trouble codes P0480, P0526, P1481 or P1484 set, which are consistent with the warning lights you described. If this is the case, have them reference technical service bulletin number 05-06-02-012B.

Skipping Camry

Q. My wife has a 2002 Toyota six-cylinder Camry with 58,000 miles. The car is in excellent shape. Every so often when traveling at 60 to 65 miles per hour, the car starts to skip. Thinking that the spark plugs may have needed to be replaced, I took the car to my local mechanic. I explained the problem to him and he informed me that I should have received a warning from the computer via caution lamp. He did a diagnostic test, which showed no warning from the car’s computer. We changed the spark plugs and the car ran well for a while but just recently began skipping again at speeds of 60 to 65 mph.

A. Since the spark plugs seemed to have helped the problem, it is possible that it’s an engine miss-fire. This could be caused by an ignition coil or intermittent wiring problem. The other possibility is that you may be feeling the torque converter clutch engaging. In early 2002, Toyota issued a technical service bulletin that addressed a surging/bucking condition at about 40 miles per hour. I would check with a Toyota dealer for additional updates.

Drive types explained

Q. As an avid fan, I was hoping you could explain the differences, if any, between four-wheel drive, full-time four-wheel drive, on-demand four-wheel drive and last, but not least, all-wheel drive. I am so confused!

A. Four-wheel drive is a system in which the front and rear wheels are connected to the transmission through a series of axles and drive shafts. In this system the driver typically engages the system with a switch or lever, from two-wheel to four-wheel drive. On-demand systems are similar to conventional four-wheel drive, except when a wheel slips the system automatically shifts into four-wheel-drive. A full-time all-wheel-drive system is one in which the front and rear wheels are engaged at all times. In this type of system, the amount of torque that is available to the front or rear wheels varies based on the amount of wheel slip.

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