Answer: You're kidding, right? With both the red "BRAKE" and amber "ABS" warning lights illuminated, you should not drive the truck until the brake problem is fixed — period! The "BRAKE" warning light indicates a potentially dangerous issue with the hydraulic brake system. The controller for the antilock brakes monitors the brake warning switch in the hydraulic combination valve, and it disables the ABS and illuminates the "ABS" warning light when the "BRAKE" warning light is illuminated.

What triggers the "BRAKE" warning light is a loss of hydraulic pressure in either half of the hydraulic brake system. You might not feel any serious brake problems when braking gradually in normal driving situations. But — this is the safety issue — it's possible that only half the hydraulic brake system is functioning properly.

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Q: I have a '98 Eldorado that blows hot air out the driver's-side vents and cold out the passenger-side vents with the air conditioning on while trying to maintain the desired 73 degrees. What do you think the problem is?

A: The sophisticated dual-zone heating, ventilating and air conditioning system on your Cadillac lets you set different temperatures for the passenger side and driver side. Check the settings on the "Pass-Temp" switch to make sure both sides are set to the same temperature. If they are, then check the air-mix valve and the aspirator hose that draws cabin air into the temperature sensor housing. A scan tool can also be plugged into the car's diagnostic link to check for HVAC fault codes.

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Q: I've got this vexing problem with a check-engine light on my 2001 4Runner. The code shows oxygen sensor issues, but my local repair guys have been unable to find out why. If I turn off the check light, the car usually runs fine for weeks, even months, and then ... the light comes on, usually when the air is on and the engine lugs a bit if I'm accelerating. This is the third time I've left the car for the day with these guys, whom I've known and trusted for decades. They haven't been able to locate the issue.

A: If they've checked for DTC fault codes, there should be a specific P-series code stored in the computer's memory. This should pinpoint the cause for the "check engine" light coming on. I would suspect an oxygen sensor issue — either a slow-to-respond front oxygen sensor or the rear oxygen sensor signal indicating an inefficient catalytic converter.

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Q: I have a 2001 Chevy truck with a 5.3-liter V8 engine and 106,000 miles. It runs fine except, when started cold, it "ticks" for about 45 seconds then quiets down. Is there an additive that will help, or is there nothing to worry about?

A: Depends on whether the "tick" is in the valve train or is the result of combustion chamber deposit interference (CCDI). CCDI is caused by light interference between carbon deposits on pistons and combustion chambers. As the engine begins to warm up, normal expansion of parts eliminates the contact — and the noise stops.