Abs Light on and Car Won T Start

Going over the river and through the woods was more dangerous back when cars had crummy bias-ply tires, rear-wheel drive, and less effective drum brakes. In today's world, you can feel confident driving home through several inches of fresh snow after a sumptuous holiday dinner. Your front-wheel drive car has excellent season-appropriate tires and an anti-lock braking system—commonly referred to as ABS.

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You know there's a problem when the ABS light turns on right before you eat the berm at the end of the driveway. You notice some strange behavior when you're slowing down for a corner, too. When you try to make a downhill turn, you blow right past it with the wheels skidding straight and the steering wheel cranked all the way into the turn.

ABS became required equipment on every new car in the United States in 2013, but automakers started to include it as standard equipment in the late 1980s. If you have a car built in the past couple decades, it probably has ABS. And that means you definitely have an ABS light.

ABS sensors tell a computer (called a controller) when a wheel stops rotating while the car is in motion, which indicates that the brakes have locked up at that particular wheel. The controller then directs a hydraulic valve to release some brake fluid pressure to the wheel in order to let it rotate again. This process repeats many times per second until the vehicle stops or you lift your foot off the brake pedal.

The ABS controller powers on to self-test every time you turn on the ignition. If that controller gets insufficient data, or a hydraulic pump or valve isn't responding, it illuminates the ABS light on the dashboard.

ABS relies on a properly operating conventional brake system. If the rest of your braking system is in working order, you should usually still have normal braking without ABS. In that case, it's safe to continue your journey. Remember what your drivers ed teacher told you about pumping the brakes when your car starts to skid? This is where that knowledge comes in handy.

But we have technology for that now! ABS can pump those brakes faster than even a racing driver can, and it can direct that pulsating brake pressure to the specific wheels that lock up. If you're having trouble with your car's ABS, look into it ASAP regardless. A malfunctioning system can have worse consequences than just lock-ups. It may pulse your brakes when you don't need it to or disable other safety features on your car.

What to Do If You See Your ABS Light

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Your ABS light is on. Now what? First, make sure it's really the ABS light and not the light that indicates an issue with your normal brakes. To rule that out, check out your regular braking system first.

A low brake pedal or grinding noise could indicate that it's time to replace your brake pads or rotors. Double-check that none of the brakes are frozen in one place, such that they drag all the time or won't brake at all. A less jarring pulsating sensation under braking may be from warped rotors instead, especially if you haven't replaced them for a while. An excessively squishy brake pedal usually means that there's air in the brake lines, and you may need to bleed your brake system or replace the brake fluid altogether.

By the way, if you ever need to replace your brake fluid, try as hard as you can to avoid getting air into the ABS controller. It's difficult to bleed, and often requires the use of a specialized ABS code reader to bleed it at all. This code-reading tool has a function that cycles the controller's pump and valves to move air out of internal passages that can't be bled properly otherwise.

If the light really is the ABS light, the first thing to try is turning the ignition key off and back on. It's like rebooting your computer. Maybe whatever transient issue that confused the ABS controller has passed and all is well. If the condition repeats, you need to do some further poking and prodding.

You have two options when your ABS light stays on. The first one is to find a shop with an ABS code reader that will talk to your ABS controller. Your dealership will have one, as will some aftermarket shops. For a modest service fee ($50 to $100), a technician will plug the code reader into your ABS controller and look for a trouble code stored in the controller's memory. This code will at least give you an idea of where to look.

If you'd rather diagnose this yourself, you'll need a service manual specific to your vehicle, and a few key tools, including a high-impedance multimeter. The service manual is extremely important, so if you can't get a paper manual, try subscribing to alldatadiy.com for service data you can download. If this is your first time using a multimeter to read electrical data, Pop Mech has a handy how-to guide here.

On some vehicles, you can access diagnostic trouble codes stored in the computer without using an ABS code reader. Usually this means pulling a connector and bridging two pins with a short wire or paperclip You may want to wear thicker work gloves if you use an unsealed wire or uncoated paperclip, though.

If what you're using has a coating on it, make sure you've got exposed metal at both ends. The ABS light will blink on and off in a pattern that corresponds to a trouble code or lack thereof. You'll need a shop manual to decode these blinks.

Let's say you don't have a blinking trouble code and no information to go on other than an illuminated ABS light. You checked the fuse for the ABS unit, right? This fuse may be in the fuse panel inside the passenger compartment or under the hood. Check your manual for the location of this fuse as well as what a healthy fuse for your car should look like.

Is the fuse okay? Then check the service manual for the voltage and resistance values on ABS-related pins and sensors. Unplug the main wiring harness to the ABS controller. While it's unplugged, clean the contacts on the plugs at the ends of these wires with a shot of aerosol contact cleaner. Inspect those contacts carefully for any signs of corrosion.

Remember that the signals traveling down some of these wires are only millivolts and almost any resistance in those wires is a major impediment for those wires to work. Check the resistance using your multimeter across the wheel speed sensors.

If the ABS controller looks A-OK and unplugging and reinserting the main harness didn't help, it's time to eyeball the wheel speed sensors—especially if your ABS light started blinking right after a trip through a snowbank or after a mucky trip down a gravel road. You may have damaged the wiring to the ABS sensors or even the tone rings or sensors themselves.

What's a tone ring, you ask? The ABS controller needs to know how fast each wheel is rotating. Somewhere on each wheel bearing assembly or axle is a toothed wheel, and there's a magnetic pickup positioned immediately next to it. Because this tone ring assembly is often out in the open, it's prone to damage from foreign objects.

⚠️Some rear-wheel drive vehicles use a three-channel system with the tone ring built into the rear differential.

Loosen the lug nuts or bolts, block the opposite wheel, and jack up the car. Truck owners may be able to crawl underneath their vehicles without jacking them up and check. Inspect the wheel speed sensor's wiring harness and the sensor itself. Some sensors are integrated fairly well into the hub and aren't prone to damage. Others are simply bolted to stamped brackets.

If the sensor is loose or missing, or the wires are damaged, you've found your problem. Check the gap between the sensor and the tone ring if it's adjustable. The shop manual will give you a specific distance the sensor is supposed to be spaced from the tone ring and directions on how to properly set it. On rare occasions, the tone ring itself will show damage, such as missing teeth or otherdamage from road debris. On front-wheel drive cars, this usually means replacing the stub axle as the tone ring is machined directly onto said axle.

If the harness to the sensor has a connector in the wheel well, pull it apart and check the sensor for continuity with your multimeter set to (surprise!) its continuity mode. For wheel speed sensors, this value is usually between 1,000 and 2,500 ohms. This resistance value can be found in the shop manual. Check for shorts to ground as well.

A ground should be a metal surface that one end of a wire goes to. Stick your multimeter probes at the end of the wire that touches the metal and the other end the wire goes to. If that reading is anything besides infinite resistance, you likely have a short. Repair any bad wiring to protect it from all the mud, snow and salt that flies into the wheel well.

When to Replace the Controller

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If you've checked all the sensors and wiring, and the ABS light still glows, it's time to throw in the towel and start looking seriously at the ABS controller. Unfortunately, the controller is an amalgam of hydraulics and electronics that has no user-serviceable parts inside. It is predictably expensive. Replace it as a last resort.

Consult your service manual for a chart of specific values and pinouts to check, which should help you narrow down the problem to a specific wire or sensor. Those could tell you exactly what is going on with your ABS and why you may be out of luck.

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Abs Light on and Car Won T Start

Source: https://www.popularmechanics.com/cars/car-technology/a461/how-to-fix-anti-lock-brakes/

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