QUESTION: I have a 2003 Mercury Mountaineer. After returning from vacation, I found a voicemail message from a neighbor who said that the car horn was blowing intermittently, which was especially irritating at night. I was skeptical until the horn sounded while I was out in the yard. I pushed the security button on the key fob, which shut it off at first but then was ineffective. But if I pushed the button to open the driver's door, the horn would stop. In order to ensure that the horn doesn't sound, I pulled the horn fuses for a temporary fix. I had also been getting a "door ajar" message on the dashboard message center, so I assume that it has something to do with one of the door sensors.

ANSWER: Your clues seem to point to the security system being triggered by an "intrusion" indicated by the door-ajar warning light. Start with a scan tool to identify any fault codes related to the horn, security system, door switches, steering column clock spring and, believe it or not, the tire pressure monitoring system. For example, a B1300-series DTC would indicate a problem with the vehicle's security system, module or door switches. The door switches are normally "closed" with the doors and liftgate closed. If corrosion, poor connections or a pinched wire in one of these switches intermittently "open" the circuit to the module, the horns sound.

Q: In reference to your column on the 2001 Cadillac DeVille transmission issue, I have a similar problem with a 1999 DeVille. Is it safe to continue to drive with the torque converter clutchsolenoid off? Could I be stranded on a highway with this problem? Also, can the TCC solenoid be replaced/fixed without transmission removal?

A: Driving your car with the TCC not engaging will not harm the transmission. The vehicle will consume a bit more fuel and may generate a bit more heat in the transmission fluid due to the small percentage of slippage in the torque converter. But, of course, until the advent of the TCC in the early 1980s, all torque converters in automatic transmissions slipped a bit while driving.

If a scan tool pulls up a TCC fault code (P0471, high TCC slippage) and confirms the lack of TCC lockup, the cause may be a sticking TCC solenoid. Assuming no other factors such as low fluid level, contaminated fluid or an electrical issue with the TCC circuit, it is possible to replace the TCC solenoid. The General Motors manual calls for removal of the transmission, but I found several articles online that outline a method for accessing and removing the transmission side cover without removing the unit from the vehicle. It's still an involved repair, so eliminate all other possible causes first.

Q: My 2006 Mustang GT has an annoying squealing noise whenever I accelerate from cold. It starts after about 0.1 kilometer and will continue for another 0.3 km. The car will only do it on the first drive of the day or when cold. The Ford dealer has observed the noise but couldn't do a thing about it. They have inspected the belts and pulleys and sprayed either the belt or pulleys with some lubricants, to no avail. The belt and one pulley have also been replaced but it didn't stop the problem.

A: It's difficult not to focus on the serpentine belt, belt tensioner and pulleys. Make sure the pulleys are all properly aligned and don't show any "run-out" or wobble. A technician could utilize a mechanic's stethoscope on a cold start to check each belt-driven component while the noise is occurring, to pinpoint the source.

I'd also check battery condition and alternator performance. High alternator output to recharge a weak or semi-discharged battery puts a significant additional load on the belt, which could be causing the squeal.

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ABOUT THE WRITER

Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn., 55488 or via email at paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, we cannot provide personal replies.

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