2015-2019 Subaru Outback ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

When the ABS light comes on in a 2015-2019 Subaru Outback, the ABS/VDC control unit has found a fault and switched anti-lock and stability control off. Your normal brakes still work, but the car will not stop skids on its own until the fault is fixed. The usual culprits are a wheel speed sensor or its wiring, a damaged tone ring, low brake fluid, or a failed brake lamp switch, and the first step is always to read the stored code.

How ABS and VDC Work Together on the Outback

This generation of Outback combines anti-lock braking and Vehicle Dynamics Control (VDC, Subaru's stability control) in one hydraulic unit and one control module. Subaru's owner information explains that VDC provides its ABS control through the ABS electrical circuit, so if ABS is inoperative, VDC cannot work either. That is why an ABS problem on an Outback almost never shows up alone: you normally see the ABS light and the VDC warning light together.

The module decides what each wheel is doing from four wheel speed sensors, one at each hub. Bosch, one of the main makers of these sensors, describes the modern design as an active Hall-effect sensor: a sealed silicon chip reads the changing magnetic field of a rotating encoder ring and turns it into digital pulses that match wheel speed, down to very low speeds. ABS and stability control both depend on that signal. If one sensor goes quiet, reads erratically, or disagrees with the other three, the module sets a code and shuts the systems down.

At start-up, the ABS, VDC and VDC OFF lights should come on briefly as a bulb check and then go out. Subaru's service information notes the lights normally clear within about 2 seconds of the engine starting (the VDC lights can take a little longer depending on coolant temperature), and some checks do not finish until the car is rolling at roughly 12 km/h. A light that stays on after that, or comes on while driving, is a real fault.

What the Light Combinations Tell You

Subaru's manual is direct about the red light: the brake system warning light also comes on when the EBD system malfunctions, together with the ABS light, and driving with it on is dangerous because the brake system may not be working properly.

The Most Common Causes, in the Order to Check Them

1. Low brake fluid

The red brake light on the Outback comes on when fluid drops near the MIN mark on the reservoir. Pads wearing down pull the fluid level down gradually, so a low reservoir on a car with thin pads can be normal wear rather than a leak. A sudden drop, wet spots at a wheel, or a soft pedal means a leak. Subaru's guidance: if the fluid is below MIN, do not drive the vehicle. Topping up without finding out why it dropped only hides the problem.

2. Wheel speed sensor or its wiring

This is the most common single cause of an ABS and VDC light on any Subaru. The sensors live at the hubs, where road salt, water and grit attack the connectors and the harness. Look for a chafed or pulled harness near the strut or knuckle, a connector packed with corrosion, or a sensor body pushed out of position. Brake jobs cause a lot of these faults: a sensor lead that gets stretched when a caliper hangs on its hose, or a sensor that gets knocked while a rotor comes off, will set the light on the first drive.

3. Tone ring or hub bearing problems

The sensor is only as good as the encoder it reads. A cracked, rusted or debris-packed tone ring, or a worn hub bearing with enough play to change the sensor air gap, produces an erratic signal. These faults often show up only over bumps or at certain speeds, and the light may clear after a restart and come back later.

4. Brake lamp switch

The ABS/VDC module watches the brake lamp switch to know when you are braking. When the switch fails, you may see the VDC light, lose brake lights, or find that EyeSight features and adaptive cruise refuse to work. Have someone watch the brake lights while you press the pedal; if they do not come on, the switch or its circuit is the first suspect.

5. Low battery voltage or a wiring or network fault

The module needs steady voltage. A weak battery, a bad ground, or a fault in the CAN network between modules can set several warning lights at once. Subaru's diagnostic procedure specifically lists the combination meter and CAN communication circuit as possible causes when the lights do not behave normally.

6. The ABS/VDC hydraulic unit or control module

Internal failure of the module or hydraulic unit happens, but it is the last thing to condemn, not the first. Rule out the sensors, wiring, fluid and voltage before replacing an expensive unit.

The Brake Lamp Switch Recall (15V-366 / WQS-54)

Subaru filed NHTSA recall 15V-366 (Subaru campaign WQS-54) covering certain 2015 model year Outbacks equipped with the driver assist system, along with some 2015 Legacy, Impreza and XV Crosstrek and 2016 WRX models, an estimated 72,000 vehicles in total. According to the recall report, if the brake lamp switch fails, the VDC system correctly detects it and turns on the VDC warning light, but the driver assist system was slow to notice. The result could be delayed notice to the driver and no automatic braking from Adaptive Cruise Control or Pre-Collision Braking. The remedy is a dealer reprogram of the driver assist system. If you own a 2015 Outback, run your VIN through NHTSA's recall lookup or ask a Subaru dealer whether the campaign was completed. The recall does not fix a failed switch itself; a bad switch still needs replacing.

How to Fix It

1. Read the codes. A basic engine-code reader usually cannot see ABS codes. You need a scan tool that reads the ABS/VDC module, or a shop that has one. The code tells you which wheel or circuit to look at.
2. Check fluid and brake lights. Two free checks that rule out common causes in a minute.
3. Inspect the flagged wheel. Follow the sensor harness from the hub back to the body connector. Look for rubbing, cuts, corrosion and loose clips. Pull the sensor, clean the bore, and check the tone ring for damage.
4. Replace the faulty part. A sensor or harness is a bolt-on repair. A damaged tone ring or loose bearing usually means replacing the hub assembly.
5. Clear codes and road test. Some checks only complete once the car is moving, so drive it before calling it fixed.

If the light came on right after a brake job, go straight to the wheels that were worked on and check sensor routing and connectors before anything else.

What to Replace at the Same Time and How Hard the Job Is

If you are already at the hub replacing a sensor, check pad thickness and rotor condition while the wheel is off. Worn pads also explain a slowly dropping fluid level. Our 2015-2019 Subaru Outback front brake kit pairs rotors and pads matched to this generation, and you can browse more brake pads and brake rotors, or brake hardware kits to refresh clips and pins while it is apart.

Difficulty: checking fluid, brake lights and connectors is easy for any owner. Replacing a wheel speed sensor is a moderate DIY job with basic hand tools, though a corroded sensor can seize in the knuckle and take patience. Hub assembly replacement is moderate to hard. Module or hydraulic unit replacement usually needs dealer-level software and a proper brake bleed procedure, so most owners leave that to a shop. Torque every fastener to the values in the factory service manual.

Frequently Asked Questions

Is it safe to drive my Outback with the ABS light on?

With only the ABS and VDC lights on, Subaru says the ordinary brakes still work, but you lose anti-lock and stability control, so drive carefully and have it checked soon. If the red brake light is also on, have the brakes inspected immediately, and do not drive if the fluid is below MIN.

Why are my ABS and VDC lights on at the same time?

On the Outback, VDC depends on the ABS circuit. Any ABS fault disables VDC too, so the two lights come on together.

Can new brake pads or rotors turn on the ABS light?

Not by themselves, but the job can. A sensor lead that was stretched, pinched or unplugged during a brake job is a very common cause of a light appearing right afterward.

Will disconnecting the battery clear the ABS light?

It may go out for a short time, but if the fault is still there the module will find it again and relight the warning. Clearing it without fixing the cause does not restore ABS.

Does the 2015 recall cover the ABS light?

Recall 15V-366 reprograms the driver assist system so it reacts properly to a failed brake lamp switch. It does not replace sensors, switches or ABS parts.

Sources

1. Subaru Outback owner information: VDC warning light - VDC uses the ABS circuit; ordinary brakes still function when ABS/VDC are off
2. Subaru Outback owner information: brake system warning light - fluid near MIN, EBD fault lights with ABS, electronic parking brake warning
3. Subaru Outback service information: VDC warning light illumination pattern - normal start-up bulb check, CAN and combination meter faults
4. NHTSA Part 573 Safety Recall Report 15V-366 - brake lamp switch detection recall, affected models, 72,000 vehicles, reprogramming remedy
5. Bosch Mobility: wheel-speed sensor - how active Hall-effect wheel speed sensors work for ABS and stability control