What's causing RAV4's tire pressure warning to light?

Q: I have a 2005 Toyota RAV4 with 115K miles. Intermittently the dashboard's tire pressure warning light comes on, even when all tires are within 4-5 pounds. This is the indirect-type TPM system associated with the ABS brakes. I use the "blinks 3 times" method to get the light to stay off after verifying pressures. The dealer has no clue what is causing this and suggested just ignoring the light. The tire store verified that the tires are OK.

Three of my tires pass the "Lincoln's head" test, but should probably be replaced this summer. One is a warranty replacement so is a slightly different diameter than the others. I think the warranty tire was installed after this problem started but I'm not sure. Where would you start to run this to ground?

A: Toyota issued a brake system service bulletin in February 2006 that indicated that the Low Tire Pressure warning light can illuminate without cause due to a lack of or improper "re-initialization" after tire replacement or tire rotation. The "blinks 3 times" procedure you described is the proper re-initialization procedure, so it's time to check the tires.

Measure the rolling diameter of each tire by one of two methods. With all four tires at equal pressure, put the vehicle on jack stands and measure the circumference of each tire with a tape measure. Or park the vehicle on dead-level ground with the steering straight, mark with chalk the pavement and each tire at the tire's center-bottom point, roll the vehicle straight forward one tire revolution and recheck each tire's chalk mark. All four marks should be at bottom center of each tire. If not, mark the pavement at each tire chalk position and measure the distance between each mark with a tape measure. This will measure the circumference of each.

Since the indirect TPM system on your vehicle uses the ABS wheel speed sensors to "look" for a wheel/tire rotational speed difference caused by low tire pressure reducing the rolling circumference of a tire, I can't help but be suspicious of the warranty replacement tire. If it is more than about 3 percent larger in circumference, it may be triggering the TPM system due to its larger circumference and different rotational speed.

Q: I would like to know what is going on with my 1998 Toyota 4-Runner. The engine makes this growling, groaning noise. It sounds like a power steering pump but the noise only appears when the weather is cold. During warm weather it hardly makes any noise. It has 160,000 miles on it, has plenty of pep and runs like a champ. I do not have any problems steering the car. Do you have any suggestions?

A: Have you ever had the power steering system flushed and refilled with fresh fluid? After 16 years and 160,000 miles, aerated and contaminated power steering fluid may well be causing the whine in cold weather. First, try adding a couple of ounces of SeaFoam Trans-Tune or similar power steering fluid additive. Better yet, have the system flushed and refilled with new fluid. I'll bet this stops the whine.