Q AND A: Diagnosing a break-light problem
Question: I have driven my Camry for 16 years and never even thought about the brake fluid other than keeping the cylinder full. About a month ago my brake warning light popped on and I don't know what caused that to happen. Today my husband siph...
Question: I have driven my Camry for 16 years and never even thought about the brake fluid other than keeping the cylinder full. About a month ago my brake warning light popped on and I don't know what caused that to happen. Today my husband siphoned half of the old brake fluid out (and it was brown) and replaced it with new fluid. The light remained on. He removed the sensor that is in the master cylinder and that made the light go out. Could it be that the sensor is bad or could I still have a brake problem? Your opinion would be greatly appreciated.
Answer: It sounds like the brake fluid level switch in your Camry initially closed, illuminating the red brake warning lamp, due to low fluid level, and is persisting, due to a sticking/binding float (part of the switch -- it's how the switch detects fluid level). The only other reasons for this lamp to glow would be a deployed parking brake, a flaky parking brake switch, or a shorted-to-ground wire leading to either switch. Since the lamp stopped glowing after your husband disconnected it, the fluid level switch is clearly the culprit.
Monitoring brake fluid level serves an additional purpose beyond indicating it's time to top off the fluid reservoir with fluid. In the unlikely even the Camry should incur a brake system hydraulic failure, perhaps due to a failed brake caliper or ruptured hose, the resulting loss of fluid would be seen by the fluid level switch, illuminating the warning lamp. Some other vehicles employ a pressure switch instead of the fluid level switch, which detects an imbalance between the vehicle's dual braking systems, indicating a serious hydraulic fault (all cars and trucks built during the past 4 decades have dual systems). With either system, in the event of a hydraulic failure, one would be alarmed to find a very low brake pedal and increased stopping effort, along with the red lamp -- but the vehicle could still be stopped.
It's perfectly normal for the fluid level in the brake master cylinder reservoir to drop -- perhaps to 1/2 of capacity, as the vehicle's disc brake pads wear. As the pads become thinner, the brake caliper pistons remain somewhat extended, borrowing fluid from the reservoir. Should the reservoir be topped off just prior to a brake job, some of the fluid will need to be siphoned off, or a messy overflow will occur when the caliper pistons are pushed back to the new-thick pad position. For safety's sake, I can't recommend leaving the fluid level switch disconnected. If fiddling with the switch, perhaps rinsing it with fresh brake fluid -- while inverted, doesn't restore it to correct operation, a replacement is needed.
Q: I recently bought a 2010 Ford Ranger Sport and returned it two days later because of a glowing battery indicator. They tested it and found a draw initially and replaced the battery saying it failed. It has run OK for a week but on the indicator panel when starting, the battery light does not seem as bright as the others. However, after starting, all lights go off. Am I worrying for nothing or does it indicate something more?
A: I wouldn't be concerned about the specific brightness of the battery lamp while cranking the engine. If the truck did have a parasitic drain (battery discharge while at rest), let's hope that was successfully corrected, or the replacement battery may suffer a similar fate. Modern vehicles, with their complex but very efficient network systems can often require up to 1/2 hour after shut-off for all modules to go to sleep, making diagnosis tricky. Hat's off to the skilled technicians that fix them right! It isn't rocket science, but it's close.