Power doors mysteriously lock, unlock during drives
Q: I own a 1997 Chevy Lumina with power door locks. Several years ago the doors began unlocking themselves after I had parked the car and locked them. Later, they began unlocking themselves while I was driving. Now, they lock and unlock while I'm driving. Neither my Chevy dealer nor GM can solve the problem. The dealer replaced the driver's side door lock switch, but the problem still exists.
Charles A: There is a trouble flow chart to test the system. The most common failure is the alarm module (body control module). A voltage test at all the connections is also required. Have the technician check all the fuses, as well as the driver's outside door handle.
Q: I own a 1995 Mercury Grand Marquis with 135,000 miles. Lately, I noticed a whining sound from under the hood. The sound changes with engine speed. What's causing the noise?
Andrew A: Have a technician look at both the power steering pump and alternator, and use a stethoscope to listen to belt-driven accessories.
Q: I own a 2000 Toyota Corolla with 103,000 miles. For the last four years the "check engine" light comes on when the temperature goes above 40 degrees. The code is p0446, indicating an EVAP problem. I replaced the gas cap and checked all the hoses.
Joe A: The most common fault has been the EVAP canister assembly located under the rear of the car on top of the subframe. There are also two additional solenoids for the system located near the air inlet. The valves and solenoids are nothing more than off and on parts that do have a high failure rate.
Q: Our 1997 Plymouth Grand Voyager has developed a hesitation problem. When started for the first time each day the engine starts fine, but after slowing for a turn and then accelerating through the turn, there is a loss of power. To prevent the engine from stalling, it is necessary to brake again slightly and then accelerate. It usually happens when first driven; the rest of the day it is fine. The car had a tune-up about six months that also included a transmission fluid flush and transmission valve body service. Any suggestions?
Cathi A: A scan tool needs to be hooked up and monitored during the hesitation cycle. It could be something as simple as a lazy idle speed control motor or EGR valve opening too soon. Is the transmission downshifting as designed? This, too, will need to be checked.
Q: I have a 2002 Corvette ZO6 with 17,000 miles. Every once in a while when I turn the key it won't turn over. After repeatedly trying it starts and all is good for a week or a month. I have used the other key because it was suggested to me the chip could be bad or dirty. I'm afraid sooner or later it will let me down. Any advice would be a big help,
Joe A: There has been trouble with the ignition cylinder. Have a technician hook up a scan tool and check for codes stored in memory.
Q: We own a 2001 Chrysler Sebring. The defroster has to be on all of the time in order to keep the windows from steaming up. We have taken the car to a Chrysler dealer and to an independent mechanic, but neither could find anything wrong. No leaks and no flapper problems were discovered. Do you have a solution to this problem?
Dave and Linda A: For the window to be steaming up -- or fogging -- indicates there is moisture in either the heater box and/or the interior or trunk. Check to see if there are any areas of wetness in the car. The reason the defroster clears the windows is because when the defroster mode is turned on the a/c compressor is activated, which clears the moisture.
Q: I'm getting a musty odor coming out of my air conditioning vents. I sprayed disinfectant and the problem resolved temporarily, but has now come back. Will I have to replace the evaporator behind the dashboard? Also, I have radio static on the AM band only. Is the problem the radio or the antenna?
Richard A: The musty smell is caused by moisture or mold buildup in the heater box. Did anyone check the drain in the box? We sometimes drill an access hole under the hood to get to the heater drain box. You need to use a disinfectant to kill off the mold, not just coat the mold. As for the static concern, does the AM band have static with the engine off? If the radio has no static with the engine off and good reception, then look into the ignition system plugs and wires for the correct parts. Any good radio shop is able to diagnose the problem.
Q: My wife's Mercedes-Benz 200D that I bought in 1971 drove beautifully, but used 1 quart of Castrol 20-50 heavy oil every 100 miles. I checked the compression and found it low, so I rebuilt the engine. I was pleased with the results until I found that it once again started burning a quart of 20-50 oil every 100 miles. After six months I got tired of putting in a quart in every week and sold it. Why did it burn heavy oil at that rate?
Sid A: When an engine is using lots of oil, it means something is using up the oil, such as a poor seal, poor sealing piston ring, sloppy valve guide or seal, or turbocharger, if equipped. The other area is the positive crank case ventilation system or, in some old cars, the PCV system.
Q: I have a 2000 Jaguar S-Type with a six-cylinder engine. During the first 20 miles the car runs great, but as the engine temperature increases it starts to "miss." From this point on it only gets worse. Changing the spark plugs seemed to help at first, but not any more. No codes come up on the code reader. Can you help me?
MaryAnn A: Some vehicles will not set a "check engine" light with an intermittent skip. A common problem in some of these vehicles is the ignition coils. Leaking valve covers onto the coils and into the spark plug wells is another common problem. Q: I own a 2002 Ford Ranger pickup with a 4.0-liter V-6 engine. The truck has over 100,000 miles on it. There is a #6 misfire and the engine idles rough. I replaced all the tune-up stuff and checked for a vacuum leak and took a compression test. What am I missing?
Ray A: There is no question that something is missing, but at this point you did everything you could. Now its time to get the truck to a qualified technician who will recheck for any vacuum leaks and do a cylinder balance test. For the engine to have a rough idle indicates a definite misfire.
Q: The airbag warning lights are illuminated on both my BMW 3 Series and my Jeep. What does the airbag warning mean? Can I just ignore the light?
Alice A: The airbag warning light illuminates because there is a problem in the airbag system. When the airbag light is on the system is shut down, meaning you have no airbag protection in the event of an impact. It could be anything from a seat position indicator to a faulty sensor. In some rare cases a simple reset of the system clears the codes and the system is fine.
Junior Damato is an ASE-certified Master Technician. E-mail questions to info@motormatters.biz. Mail questions to: Auto Doctor, 3 Court Circle, Lakeville, Ma., 02347. Copyright 2008, Motor Matters. The Auto Doctor