Mechanics

ABS & BRAKE LIGHT ON

1997 Dodge Ram

Brakes problem
1997 Dodge Ram V8 Two Wheel Drive Automatic 90000 miles

I had 2 brake lines break and have replaced them and bleed out lines and have good brakes. My ABS & brake lights are still on the dash. What's up with that?
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Haukster
December 7, 2009.




Most likely a simple fix. When you popped a brake line, the pressure differential valve shifted which turned on the red warning light. Now that you have a solid pedal, that light should go off. The valve is spring-loaded on Chrysler and GM vehicles, but it can get stuck if there is any corrosion in the valve body. Usually a good hard jab on the brake pedal will release the stuck valve. If it doesn't, you will have to open the hydraulic circuit that did not have the leak, then slowly push the pedal down until the light turns off, then tighten the fitting before releasing the pedal or air will be drawn in. (You'll need a helper for that operation).

The same light can be turned on by the parking brake pedal and the low brake fluid switch. Be sure the brake fluid is full, and try pulling up on the parking brake pedal to be sure those aren't the cause of the red light.

One word of warning; when the vehicle is more than about a year old, NEVER push the brake pedal all the way to the floor. Stop when it gets half way down. Pushing it all the way to the floor, which is what most do-it-yourselfers do when bleeding the brakes, runs the lip seals in the master cylinder over corrosion in the bottom halves of the bores where they don't normally travel. Ripped seals will cause a low or slowly sinking pedal, and the master cylinder will have to be replaced.

Depending on whether you have four wheel anti-lock brakes or rear wheel ABS, the computers and hydraulics work differently, but both do some self tests when you first start the engine. On the RWAL system, driving for any distance with the red warning light on will disable the ABS and turn on the yellow warning light. The computer knows there is a problem with the hydraulics that will affect ABS system performance so it shuts down.

The four-wheel ABS system also performs self tests which include monitoring very highly pressurized brake fluid stored in an accumulator. When pressures are too low to provide proper ABS operation, the system shuts down and the yellow light is turned on. In both systems, there will be a diagnostic fault code memorized indicating the reason the light is on. To turn the light off, the fault code(s) must be read with a hand-held computer that can also erase them. Disconnecting the computer or the battery will not erase the codes in the RWAL computer. They can only be erased with the hand-held computer.

There weren't very many trucks with the four wheel ABS system. At least I don't remember working on any from the mid to late 1990s. If you do indeed have the four wheel ABS system, you can try disconnecting the computer or the battery for a minute to see if the light goes out. If it doesn't, you'll have to take it to a shop with the hand-held computer, (called a scanner). I use Chrysler's DRB3. Aftermarket scanners don't do as many functions or access as many systems as the manufacturer's equipment, so this might be a job for your local Chrysler dealership mechanics.

If you do disconnect the battery, be aware there are other issues you will cause. Short and long term fuel trim data that took days or weeks to memorize will be lost. The engine computer will have to relearn that and the various sensor readings and their relationship to each other. That process could be partially completed in a matter of a few miles to the point where you think the engine performance is normal. You will also have to relearn minimum throttle by driving at highway speeds with the engine warmed up, then coasting for at least seven seconds without touching the brake or gas pedals. Until you do that, the engine will not idle on its own without you holding you holding the gas pedal down about 1/4".

Caradiodoc

Caradiodoc
Dec 8, 2009.


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