1993-1998 Toyota Supra ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

An ABS light that stays on in a 1993-1998 Toyota Supra means the ABS computer has found a fault and switched anti-lock off. Your normal brakes still work. The good news is that this car can tell you which fault it stored without a scan tool: jump two terminals in the diagnostic connector and the ABS light blinks out a two-digit code. On a Supra this old, most codes point to a wheel speed sensor, its tone ring, the wiring, or low system voltage rather than the expensive actuator.

How the ABS System Works on the Mk IV Supra

The Toyota factory repair manual for the 1997 Supra lays the system out in a few main pieces: an ABS ECU (the computer), an ABS actuator (the hydraulic unit with solenoids and a pump motor), a solenoid relay and a motor relay, a speed sensor at each wheel, and the ABS warning light in the gauge cluster. Turbo (2JZ-GTE) cars add a deceleration sensor, and some turbo cars were built with traction control (TRAC), which has its own TRAC OFF indicator and its own diagnostic section in the manual.

Each wheel speed sensor is a passive magnetic sensor. The manual explains that the front and rear sensor rotors each have 48 teeth, and as a rotor spins past the sensor's permanent magnet it generates an AC voltage whose frequency rises with wheel speed. The ECU compares those four signals to spot a wheel that is about to lock. Because this signal comes from magnetism across a small air gap, anything that weakens it - rust, metal debris, a damaged tooth, a loose sensor, a broken wire - can set a fault.

When you turn the key on, the ABS light should come on for about 3 seconds as a bulb check and then go out. If it stays on, or comes on while driving, a code is stored.

How to Read the ABS Codes (No Scan Tool Needed)

The 1993-1998 Supra predates generic OBD-II ABS reading, but Toyota built in a blink-code readout. The factory procedure is:

1. Turn the ignition switch ON (engine off).
2. Remove the short pin from the DLC1 diagnostic connector in the engine bay.
3. Connect terminals Tc and E1 of DLC1 (or DLC2 under the dash) with a jumper wire.
4. Count the blinks of the ABS warning light. A two-digit code shows as the first digit's blinks, a short pause, then the second digit's blinks. A steady, even blink cycle is the normal (no fault) code.
5. If more than one fault is stored, the lowest-numbered code is shown first.
6. When finished, remove the jumper and reinstall the short pin.

If the light will not blink a code at all, the manual sends you to the warning light circuit and the Tc terminal circuit before blaming the ECU.

What the ABS Codes Mean

These are the codes listed in the factory diagnostic chart for the Mk IV Supra, with the most likely trouble areas:

On cars this age, the 31-34 speed sensor codes and code 41 low voltage are the likeliest, because they come from corrosion, wiring fatigue and weak charging systems rather than a failed module.

Common Causes and How to Fix Each One

Wheel speed sensor or tone ring (codes 31-34)

The factory test for a speed sensor is a resistance check across the two sensor terminals, plus a check that neither terminal is shorted to body ground. Toyota's specs for this car are 0.6 to 2.5 kilohms for a front sensor and 0.65 to 1.8 kilohms for a rear sensor, with 1 megohm or more to ground. The front connector is reached by removing the front fender splash shield; the rear connectors sit behind the rear seat cushion, seatback and quarter trim panel, so plan for some interior work.

If the sensor measures good, check the wiring between the sensor and the ECU for opens and shorts, then inspect the sensor rotor and mounting. The manual calls for rotor teeth with no scratches, missing teeth or foreign objects, a sensor tip that is clean and undamaged, and a sensor bolted down tight with no clearance between the sensor and the steering knuckle (front) or rear axle carrier. Checking the rear sensor rotor requires removing the drive shaft, which is why it is usually checked last.

Brake trade references note that on passive sensors like these, rust building up under the sensor mount lifts the sensor away from the tone ring, widens the air gap and weakens the signal. Metal filings stuck to the magnetic tip also cause erratic readings. Cleaning the sensor tip and the mounting surface often cures an intermittent 31-34 code on an older car. Worn wheel bearings that let the tone ring wobble can cause the same thing.

Low voltage (code 41) and light always on

The ABS ECU watches its supply voltage. A tired battery, a weak alternator regulator, or a corroded power feed can set code 41, and a loss of power to the ECU turns the light on with no code. Test the battery and charging voltage before touching any ABS part.

Brake light switch (code 49)

The ECU uses the stop light switch to know when you are braking. An open in that circuit sets code 49. Check that your brake lights work - a failed switch or an open in the circuit can also leave you without brake lights, which is a safety issue on its own.

Relays, actuator and pump motor (codes 11-24, 51)

These point to the hydraulic unit side. Check relays, connectors and grounds first, since those are cheap and common. The actuator is the last suspect: the factory troubleshooting table only calls for replacing the ABS ECU after the codes, power supply, speed sensor circuits and an actuator check all come back normal.

Clearing the Code After the Repair

Disconnecting the battery does not erase ABS codes on this car. With Tc and E1 jumped, the short pin removed and the ignition on, press the brake pedal 8 or more times within 5 seconds, then confirm the light shows the normal code. For motor relay (13), speed sensor (31-34) and pump motor (51) codes, the manual adds that replacing the part alone will not clear the code: either clear it with the pedal procedure or drive the car at 12 mph (20 km/h) or more for at least 30 seconds.

What to Replace at the Same Time

ABS faults often show up around brake or suspension work, because that is when sensors get knocked, wires get stretched, and tone rings get exposed to dirt and brake dust. If you are chasing a speed sensor code, look at the rest of the corner while it is apart:

• Pads and rotors. If the brakes are due, doing them while the sensor and hub are accessible saves labor. We carry a 1993-1998 Toyota Supra front and rear brake kit, plus individual brake pads and brake rotors.
• Brake hardware. Fresh clips and slide hardware from our brake hardware kits keep new pads quiet and wearing evenly.
• Brake hoses. Decades-old rubber hoses run right beside the sensor wiring; inspect them and see our brake hoses if they are cracked or soft.

Handle sensor wiring gently, keep the sensor tip clean, and route harnesses back into their original clips so they cannot rub on a tire or hose.

How Hard Is This Job?

Reading the codes is a five-minute job with a jumper wire. Testing a sensor with a multimeter is easy for a home mechanic. Replacing a front sensor is moderate; rear sensor work is harder because of the interior trim and, for rotor inspection, drive shaft removal. Actuator and ECU diagnosis is best left to a shop with the right equipment, and any work that opens the ABS hydraulic lines requires a correct brake bleed afterward.

Frequently Asked Questions

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

The normal brakes still work, but anti-lock will not function, so the wheels can lock in a hard stop or on a slippery road. Drive carefully and repair it soon. If the red brake warning light is also on, check the brake fluid level and the system before driving.

Can I read Supra ABS codes with a normal OBD-II scanner?

Not reliably. These cars use Toyota's blink-code system: jump Tc and E1 in the diagnostic connector with the short pin removed and count the flashes of the ABS light.

Will disconnecting the battery turn off the ABS light?

No. Toyota's manual states that disconnecting the battery will not erase the ABS codes. Use the brake pedal procedure with Tc and E1 jumped, or for some codes, drive at 12 mph or more for 30 seconds after the repair.

Which wheel does ABS code 33 mean?

Code 33 is the right rear wheel speed sensor signal. Code 31 is right front, 32 left front and 34 left rear.

Can a weak battery turn on the ABS light?

Yes. Code 41 is low battery voltage, and it points to the battery, the alternator voltage regulator or the power feed rather than an ABS part.

Do I need to replace the whole ABS actuator?

Usually not. Many faults on these cars are sensors, tone rings, wiring, relays or voltage, and the factory procedure checks all of those before condemning the actuator or ECU.

Sources

1. Toyota 1997 Supra Repair Manual (RM502U), Anti-Lock Brake System diagnostics - DTC chart, blink-code and clearing procedure, speed sensor resistance specs, 48-tooth sensor rotors, inspection steps
2. Toyota Supra Repair Manual, Diagnostics section (alternate copy) - diagnostic flow and problem symptoms table
3. MOTOR Magazine - Brake Shop: Wheel Speed Sensors - how passive sensors work and common failure causes (debris, rust, air gap, tone ring damage, bearings)
4. Brake and Front End - ABS Light On or False ABS Activation - rust under the sensor mount widening the air gap