Troubleshooting a wonky brake warning

Q&A

Question: The red brake warning light on my 2005 Ford F-150 comes on at various times. Can you suggest what I might do to check for the cause? T.M.

Answer: According to my ALLDATA wiring diagrams, your F-150 has three possible or intended causes for the red brake indicator to illuminate.

First is the bulb-check process when you roll the key to the crank position as you start the engine. This proves the light bulb works.

Once the truck is running, the other two possible causes are the parking brake switch and the master cylinder reservoir low-fluid level switch. A grounded wire leading to either switch is a distant fourth possibility.

Let’s start by checking the master cylinder fluid level. If it is low, filling it should do the trick to extinguish the light. Use only fresh DOT 3 brake fluid from a sealed container. A low reservoir is cause for further investigation. It would be prudent to check brake lines, hoses, calipers and master cylinder for leakage. It’s also possible the fluid level is low due to extended caliper piston positions as a result of worn or thin brake pads. This is the more likely situation.

If the fluid level looks OK, we’ll next look for a faulty low-fluid warning switch. It sounds like the light is intermittent, so you’ll need to wait until the next time it comes on to do the following: With key on and engine off, unplug the master cylinder fluid reservoir’s threeterminal connector. If the light goes out, there is something wrong with the fluid-level float switch.

The parking brake switch is next. It’s a bit more difficult to get to, as it is located on the foot pedal mechanism. Try this first: Pull back and hold the brake release handle, and slowly press the pedal up and down a couple times near the top of travel, observing the warning light like a hawk. If it remains on at the exact same intensity, the parking brake switch warrants further inspection. If the light changes in intensity even slightly as the pedal is operated, the parking brake switch is probably not the cause (light is already on due to another cause, becomes brighter due to two ground paths).

Next, try pulling the pedal back slightly beyond its top-stop with the top of your toes while pulling on the release. If this cancels the warning light, the switch requires adjustment or repair.

Now it might be time to get a little dirty and torque your back. Unplugging the single wire leading to the parking brake switch will cancel the light if it is the offending part. Sometimes these primitive switches come loose or fall apart, or if the wire leading to it becomes snarled in the ratchet mechanism, the resulting grounded circuit will turn on the light, likely intermittently.

Q: I was just told when having my tires rotated on my Yukon 4x4 that my right front-wheel bearing was loose. Being an oldtimer, I’ve done wheel bearings before. I was surprised to see there isn’t a dust cap as I’ve had in the past. What gives?

C.G. A: Your Yukon, like other GM light trucks, utilizes an integrated hub/wheel bearing/brake sensor assembly. Previously quite expensive, these hubs have come down to about $150 for a name-brand part (don’t go cheaper). Installation requires a little over an hour’s labour, some large wrenches/sockets and a few choice words.

Q: We take several extended vacations in the winter. I found that it is imperative that I get the undercarriage thoroughly washed before leaving the car parked during an extended vacation. Before I started doing that, the rotors became severely rusted and sometimes damaged.

The problem is likely the salt that the car had been exposed to before it was parked. Even if it has not snowed for several days or even weeks, there is usually salt residue on the roads until we get heavy spring rains.

D.M. A: Excellent advice. I used to plow small parking lots with a 4x4 pickup, and seldom washed the undercarriage. When I was selling it, the buyer bargained us down due to the amount of rust underneath.

Q: The sway bar in my 12-yearold Corolla has loosened, causing much rattling. I’m told I can replace it for a reasonable cost, but that it isn’t necessary and won't cause any problems even if it fails. My question for you is: Will this rattling cause other problems in the car?

S.K. A: The rattling probably will do no harm, but I would still suggest getting the sway bar (more properly called an anti-sway bar) replaced. Its job is to force the outside wheel down when cornering. Without the sway bar, that wheel tries to rise off the road.

Q: Here’s how to fix the problem of snow filling the bridges of your wiper blades: Lower your window all the way, lean forward close to the steering wheel, and stick your arm out and around to the front side of the windshield. The next time the blade swings left, jam your fingers under the squeegee and raise it up 2 or 3 inches off the windshield, so that as it swings back to the right and out of your reach, it snaps back down against the windshield.

In heavy show, you might have to do this twice or even three times. And watch where you’re going.

S.T. A: Risk your safety and that of others just to clear the snow from one wiper? You have got to be kidding. Spend a couple more dollars and buy beam blades. Hospital stays are way more expensive.

Q: Horst, my German-born brother-in-law who reminds me that he’s an engineer, complains that the A/C hasn’t worked in his expensive truck since day one. Dealership states nothing is wrong every time. I mentioned opening windows to vent hot air out. I open my window a hair; he closes it. This little game went on for a while until I couldn’t tolerate the heat.

I opened the glove compartment, retrieved the manual and read aloud the section about cracking the windows open to vent the hot air out of the vehicle. Lo and behold, the air conditioning works great.

O.W. A: Any engineer worth his salt should know that a vehicle moving through the air will cause negative air pressure (vacuum) outside vs. the air pressure inside the vehicle. It is similar to what keeps airplanes from falling. Lower air pressure above the wing causes lift — the Bernoulli effect.

You might want to ask your brother-in-law what railroad he worked for. Brad Bergholdt is an automotive technology instructor at Monterey Peninsula College in Monterey, California. Readers can email him at bradbergholdt@gmail.com. Personal replies are attempted.