2009 Suzuki SX4: Brake Warning Light Mystery Solved
January 12, 2010
Just before the holidays our 2009 Suzuki SX4 started to intermittently display brake system warning light. This indicator happens to be red and federal safety regulations reserve this color for Serious Business such a brake system problems or air bag faults, so this is not a "live with it" situation.
The light routinely comes on when the parking brake is engaged as a reminder to release the brake before driving off. I check to see if the switch near the parking brake handle was faulty, but that was a dead end.
Next stop: under the hood for a look at the master cylinder...
The master cylinder has a electronic sensor that monitors brake fluid level. If the fluid level gets too low it will turn on the same dashboard warning light used by the parking brake. If the brake is released and the switch seems predictable, look here.
Two visual references are molded into every master cylinder reservoir. Here the Max level (black) is high and dry and the Min level (yellow, just visible below the joint line) looks marginal. My driveway is far from level and on flat ground the fluid level corresponds to Min line. We have found the reason for the warning lamp.
But I need to look around before I add any brake fluid. There are no obvious leaks, so where could the fluid have gone? Into the brake calipers, of course. As brake pads wear down over time, the pistons protrude further and further out and the caliper bores draw and hold a gradually increasing amount of brake fluid. There is no leak, the brake pads are simply wearing down and the fluid level indicator is serving as an ersatz pad wear indicator.
A quick check of the pads confirms this. The rear pads look quite thick, but the front ones are looking thin. Not thin enough to change, mind you (this is where the ersatz part comes in), but thin enough to make a mental note that a change is due soon. I give them no more than a month.
Instead I added a little brake fluid from my personal stash to shut off the light and keep the level above Min.
It's clearly above the Min line now and the sensor should be immersed. But it's nowhere near Max. When didn't I fill it all the way? Well, when the pads are eventually changed the pistons will have to be pressed back into the calipers to make room for the new, thicker pads.
The fluid that's displaced during that process has got to go somewhere, and that somewhere is back up into this reservoir. If I fill it to Max now, the master cylinder will overflow and spill out the top when the pads are installed later if I forget to take a turkey baster and suck some out during the process and dispose of it someplace.
Success! The light is back out, illuminating only when the parking brake is set. Now for the bad news: Our 2009 Suzuki SX4 will be lucky if it sees 23,000 miles before it needs a set of front brake pads. That seems a bit short for a car that isn't particularly speedy and spends little time in the mountains.
Dan Edmunds, Director of Vehicle Testing @ 20,174 miles