Q: My 2000 Ford Explorer 4-liter Control-Trac 4WD has 120,000 miles on it. At 84,000 miles the O/D (overdrive) light began flashing randomly. The shop identified fault code P0741, indicating a potential issue with the transmission. I chose to keep driving the vehicle and the transmission has not failed yet, but I've noticed something peculiar. The light will begin flashing at specific locations on the routes I commonly take, and always where there is a power line overhead. It is also directional. The light will flash, for example, if I'm headed north but not if I'm headed south on the same road. Is there a sensor that could be sensitive to temperature and magnetic flux? Is the transmission failing?

A: Magnetic flux? Interesting thought, but highly unlikely. (I did have an early computerized fuel-injected vehicle — a beautiful '77 Cadillac Seville — that could be turned off by keying the microphone on a nearby handheld walkie-talkie. Took a while to figure what was shutting down the car as I drove out to a corner of the racetrack to observe my Skip Barber students! Apparently, the RF signal from the radio was interfering with the PCM and shutting down the engine.)

But as much as I'd like to believe that "magnetic flux" could be the culprit, the fact that the event only seems to trigger the O/D warning light rather than affecting any or all of the other computerized systems in your vehicle points to some more earthbound cause.

The P0174 code is triggered when the PCM detects excessive torque converter clutch (TCC) slippage under normal driving. Have you noticed whether the light comes on as you are driving slightly uphill? The extra load on the drivetrain may generate excess slippage in this location, but of course driving in the opposite direction on the same piece of road would be downhill, far less likely to generate TCC slippage.

TCC slippage does not mean impending transmission failure, but it does mean the TCC is worn, the transmission fluid is significantly contaminated and/or hydraulic pressure is somewhat low. At the current mileage my suggestion is to add half a can of SeaFoam Trans-Tune to the transmission fluid and hope this reduces the symptoms, and continue to drive the vehicle until something catastrophic happens — then decide whether to repair or replace the vehicle.

Q: I recently purchased and am restoring a 1971 Volvo 1800E. This car is fuel-injected. Do you believe it is necessary to use a lead alternative additive until the day I need a valve job and can add hardened valve seats? Should I try to purchase non-oxygenated gasoline?

A: This is an older question I "rediscovered" recently, but since it's the heart of the summertime collector-car driving season, I thought it worth answering — sorry for the delay.

To my knowledge, most carmakers were installing hardened valve seats by about 1970, so I don't think you need to be particularly concerned about excess wear unless you are really "leaning" on the engine — full throttle, high RPM — regularly. Most so-called lead substitutes are not actually tetra-ethyl lead, which is no longer permitted in highway-use motor fuels, they are similar "metallics" that hopefully perform the same cooling and lubricating functions to prevent valve seat overheating, sinking and erosion.

I do, on the other hand, believe you should seek out, purchase and use non-oxy fuel for your older vehicle to protect fuel system components from contamination and corrosion. These parts, including the fuel tank and fuel lines, were not designed for oxygenated fuels.