1997-2001 Mitsubishi Montero ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

An ABS light on a 1997-2001 Mitsubishi Montero means the anti-lock control unit has found a fault and switched the anti-lock function off. Your normal brakes still work, but the wheels can lock in a hard stop. On these trucks the most common causes are a wheel speed sensor circuit, a damaged or dirty ABS sensor rotor (tone ring), or a worn wheel bearing, and the stored trouble code tells you which corner to start at.

How the Montero ABS System Works

Every anti-lock system does the same basic job. Bosch describes it this way: each of the four wheels has a wheel-speed sensor, and a hydraulic unit with valves, a return pump and an electronic control unit reduces braking pressure on a single wheel that is about to lock, then raises it again once grip returns. That cycle repeats many times a second, which is the pulsing you feel through the pedal in a panic stop.

Mitsubishi's ABS workshop manual for the 2001 Montero 4WD shows the parts involved on this truck:

• Wheel speed sensors at all four corners, each reading a toothed ABS rotor.
• G sensor, which measures how fast the vehicle is actually slowing so the computer can judge wheel slip on a 4WD truck where all four wheels may be turning together.
• ABS-ECU and valve relay, the control unit and the relay that powers the solenoid valves.
• Stop lamp switch and the center differential lock or 4WD detection switch, which change how the system behaves.
• Hydraulic brake booster (HBB) on the 2001 model, which uses a pressure accumulator instead of engine vacuum for power assist.

Because the 1997-2001 span covers a generation change for the full-size Montero, and the Montero Sport is a separate model, confirm the exact layout for your truck in the factory manual for its model year before buying parts. The diagnosis logic below comes from the 2001 Montero ABS manual.

What the Light Should Do, and When It Is a Real Fault

According to the Mitsubishi manual, the ABS warning lamp should come on for about 3 seconds when the ignition is turned to ON, START and back to ON, then go out. That is the self-check. If it stays on, or comes on while you drive, the ABS-ECU has stored a diagnosis code.

One detail catches people out: if a wheel speed sensor code was stored earlier, the lamp can stay lit after start-up until the truck reaches a few km/h, because the computer has to see the sensor working again before it clears the lamp. A light that goes out as soon as you pull away, then returns later, usually points to a sensor problem that is intermittent, not fixed.

Keep the amber ABS lamp and the red BRAKE lamp separate in your head. The red lamp relates to the base hydraulic system and parking brake. If both are on at once, treat the brakes as suspect and have the truck checked before driving it.

Reading the Trouble Codes

Mitsubishi's procedure reads codes with the MUT-II scan tool on the 16-pin diagnosis connector, or by counting ABS lamp flashes. Codes cannot be erased while the ECU has shut the system down in fail-safe, so fix the cause first. The table lists the main codes from the 2001 Montero ABS inspection chart.

The manual notes that code 16 erases itself when the condition returns to normal, so a weak battery or charging problem can set it and then leave no trace. Check battery condition before chasing a power-supply code.

Common Causes on These Trucks

Wheel speed sensor and wiring

For codes 11 to 14, the manual's probable causes are the sensor itself, the harness or connector, the ABS-ECU, the ABS rotor, excessive clearance between the sensor and rotor, and wheel bearing trouble. The sensor wiring runs past the suspension and gets stretched, chafed and corroded, especially on a truck that has been off-road or through road salt. The manual's first check is the sensor resistance measured at the ABS-ECU connector; a reading out of the specified range sends you to the sensor or wiring for that wheel.

ABS rotor (tone ring) and sensor gap

The manual calls out a chipped or plugged-up rotor tooth as a detectable cause. Rust scale, packed mud or metal debris stuck to the sensor tip can distort the signal enough to set code 15 even though the sensor measures fine on a meter. Clean the sensor tip and inspect every tooth.

Wheel bearings and tires

Play in a wheel bearing lets the ABS rotor move away from the sensor, so the signal drops out on bumps and in turns. For code 15, Mitsubishi also lists uneven tire size across the four wheels. Mismatched tires, or one tire far more worn than the rest, make one wheel turn at a different speed and can look like a sensor fault to the computer. After fitting new tires, make sure all four are the same size.

Low voltage and stop lamp switch

A tired battery, loose ground or poor charging can set the ECU power-supply code. A failed stop lamp switch sets its own code and also affects your brake lights, so check that the brake lights work.

Hydraulic brake booster on the 2001 Montero

The 2001 Montero uses a hydraulic brake booster with an accumulator, and the ABS manual gives it its own code (55). NHTSA recall 01V254001 covered accumulators on these boosters that may have been improperly made and could leak nitrogen gas. The recall notice says that could cause an abnormal noise from the left side of the dash when braking and a delayed first brake assist after the truck has been parked. If your truck shows those symptoms, run the VIN for open recalls before buying parts.

Brake Recalls and Related Faults to Rule Out

Not every warning on these trucks is an ABS electrical fault. Two other NHTSA brake recalls apply to this span:

• 98V220000 (1997-1998 Montero): the front brake lines can wear pinholes where they chafe against the pass-through hole in the inner fender. Leaking fluid can reduce braking and turn on the brake indicator lamp. If you see wet lines or a dropping fluid level, replace the damaged line with new brake lines and bleed the system.
• 01V027000 (1999-2001 Montero Sport with the 3.5L engine): these trucks were built with brake vacuum hoses that did not meet FMVSS 106. A failed vacuum hose means lost power assist and a hard pedal. The Montero Sport uses a vacuum booster; if the hose is good and the pedal is still hard, test the booster. We carry a vacuum power brake booster for the 1997-2001 Montero Sport.

The Fix, What to Replace Together, and How Hard It Is

Work in this order: read the code, check battery voltage, then go to the wheel the code names. Unplug and inspect the connector, measure the sensor, clean the sensor tip and ABS rotor, and check for bearing play. Replace only what fails a test. A new sensor will not fix a chipped tone ring or a loose bearing.

Brake work often disturbs the sensor. If you are replacing brake rotors or brake pads on the Montero, route the sensor wire back into its original clips so it cannot rub on the rotor or stretch at full steering lock. That is a good time to replace brittle brake hoses too.

Difficulty: cleaning a sensor and fixing a connector is basic driveway work. Replacing a sensor is moderate; seized sensors in the knuckle are common on older trucks and need penetrating oil and patience. Bearing and hub work on a 4WD front end is harder, and hydraulic unit or HBB repairs, plus bleeding after them, are jobs for someone with the factory manual and a scan tool. Torque every fastener to the value in the factory service manual. Browse our full range of brake parts for the rest of the job.

Frequently Asked Questions

Is it safe to drive a Montero with the ABS light on?

The base brakes still work, but the anti-lock function is off, so the wheels can lock in a hard stop, especially on wet or loose surfaces. Drive gently and get it diagnosed. If the red BRAKE light is on as well, have the brakes checked before driving.

Why does my ABS light go out after I start moving?

Mitsubishi's manual explains that after a stored wheel speed sensor code, the lamp can stay on until the truck reaches a few km/h and the computer sees the sensor working again. It points to an intermittent sensor, wiring or tone ring problem.

Can I read the ABS codes without a scan tool?

The factory procedure allows reading codes from ABS lamp flashes as well as with the MUT-II tool. The exact method depends on model year, so follow the factory manual for your truck. A scan tool that reads Mitsubishi ABS is faster and shows live sensor data.

Can new tires turn on the ABS light?

Yes. Mitsubishi lists uneven tire size across the four wheels as a cause of the abnormal sensor output code. Keep all four tires the same size and similar wear.

Will replacing the brake pads turn off the ABS light?

No. Worn pads do not set ABS codes. The light only clears once the fault the code points to is fixed, although careless pad or rotor work can damage a sensor wire and cause one.

Sources

1. Mitsubishi Montero 2001 ABS 4WD workshop manual - system components, warning lamp self-check, diagnosis code chart and probable causes
2. Bosch Mobility: Antilock braking system - how wheel speed sensors and the hydraulic unit prevent wheel lock
3. NHTSA recalls, 2001 Mitsubishi Montero - recall 01V254001, hydraulic brake booster accumulator
4. NHTSA recalls, 1998 Mitsubishi Montero - recall 98V220000, front brake line chafing
5. NHTSA recalls, 2000 Mitsubishi Montero Sport - recall 01V027000, brake vacuum hose