Brake light on for no reason?
The red brake warning light on my 2005 F-150 comes on at various times. Can you suggest what I might do to check for the cause? — Ted
According tomy ALLDATA wiring diagrams your F-150 has three possible/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 running, the other two possible causes are the parking brake switch and themaster 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 low, filling it should do the trick, extinguishing the light. Use only fresh DOT 3 brake fluid from a sealed container. A low reservoir is cause for further investigation. An inspection of brake lines, hoses, calipers, and master cylinder for leakage is a prudent action. It’s also possible the fluid level is low due to extended caliper piston positions as a result of worn/thin brake pads. This is the more likely situation.
Should the fluid level look 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/engine off, unplug the master cylinder fluid reservoir’s 3-terminal 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 pedalmechanism. 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 isprobably 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 it’s topstop with the top of your toes while pulling on the release. If this cancels the warning light, the switch requires adjustment or repair.
Now itmay 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 should the wire leading to it become snarled in the ratchetmechanism, the resulting grounded circuit will turn on the light, likely intermittently. I was just told when having my tires rotated on my Yukon 4x4 that my right front wheel bearing was loose. Being an old timer 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? — Carl G.
Your Yukon, like otherGMlight trucks, utilizes an integrated hub/wheel bearing/brake sensor assembly. Previously quite expensive, these hubs have come down to the $100-150 range for a name brand part (don’t go cheaper). Installation requires a little over an hour’s labor, some largewrenches/ sockets, and a fewchoice words.