Q: My 2006 Cadillac DTS has had a battery problem ever since I purchased it used in 2010. The morning after I bought the car, it would not start due to a dead battery. The dealer replaced the battery but the car continued to have this problem intermittently. They eventually installed a trickle charger because they said I didn't drive the car enough to recharge the battery. They never did check for a short or drain on the battery. Since installing the charger I no longer have the dead battery problems, but I can't take the car anywhere for a few days where there isn't access to an electrical outlet. Is there some defect in the car's electrical system or does this car have such a high current drain that it's an inherent issue?
A: The simple diagnostic procedure for excess current draw is to connect an ammeter in series with the negative battery cable so that the ammeter "sees" any current flow from the battery with the ignition switched off. Typically, the parasitic draw is less than one-tenth of one ampere. If the meter shows excess current flow, pull each fuse and relay until the current stops — you've identified the fault circuit.
But in your case, the problem may be related to a specific issue. My ALLDATA automotive database pulled up GM service bulletin 09-08-50-017B dated February 2010 that points to the rear heated seat module (RHSM) as a potential culprit. Apparently, it can keep the serial data buss alive after shutdown, which can cause a 4-amp draw until the battery drops below three volts.
The "fix" is to have the dealer reprogram the RHSM. You could try removing the 20-amp fuse for the RHSM located in the F32 position in the rear fuse block under the rear seat. If that prevents the dead battery syndrome, you've found the culprit.
Q: Please cover in more detail how to handle low tire pressure in subzero conditions. Every year on the coldest day I'm out there trying to put air in my tires because the sensor says they're low. Your recent column indicates I shouldn't be adding air in these conditions. What should I do?
A: Add air to the tire before it gets cold. Since tire pressures fall roughly 1 psi per 10-degree F. drop in air temperature, add 5 psi to each tire in late fall before temperatures drop below freezing.
Q: Recently I asked my Toyota dealer if the brake or power steering fluid in my 2006 Avalon needed changing. He said Toyota has no recommendation for these fluid changes but that Lexus does. Why the difference?
A: I confirmed that the Lexus does recommend brake fluid changes every 30,000 miles on the ES330 — virtually an upgraded Avalon. This is also my recommendation for every vehicle to keep the brake system clean and free of moisture and corrosion.
Why the difference? Certainly there's no technical reason — perhaps it's the difference in buyers. Perhaps Lexus owners are a bit more "invested" and interested in their vehicles?
Motoring note: More on slow tire air leaks. From Keith Myhre: "My 2008 Lexus has standard factory wheels with metal valve stems and caps for the tire pressure sensors. One wheel had a slow leak for several years. I tried the normal cures — reseating the tire, cleaning the metal rim and tire bead, checking the valve cores. Even a set of new tires didn't solve the slow leak.
I eventually discovered the cause. The valve core didn't leak with the cap off but did leak with the cap fully tightened, as confirmed by soapy bubbles. It looks like a tiny protrusion of metal in the center of the metal cap impinged on the valve core stem when screwed on tightly. Backing off the tightened cap by one-sixteenth of a turn solved the problem. None of the other metal caps had this problem.