Brake accumulator has lost its charge

The third generation's brakes are assisted by a hydraulic booster with a gas-charged accumulator bolted to it, and that accumulator is the single most reported fault on this truck. Mitsubishi recalled it for the first two model years this generation was sold in North America: the campaign says the accumulator may have been improperly manufactured, that it can leak its pressurised nitrogen over time, and that the result is an abnormal noise from the left of the dash panel plus a delayed first application of boost after the truck has been parked. Owners describe the noise the same way in every language — a chirp, a gobble, the honk of a goose — and the specialist supplier who sells the replacement names the same sound as the telltale. Two things this entry is careful about. The campaign covered vehicles built up to a cut-off date partway through its first year, and owner after owner reports the identical failure on a truck whose VIN is not on the list — including filings from later model years, each cited below and confirmed as a full-size Montero by its VIN. The entry therefore claims no factory authority outside the campaign's own years, and its tier reflects that. And the triage is not this site being cautious: one owner's mechanic told him not to drive it until it was repaired, another lost the brakes entirely at highway speed, and a third was told the truck could not be driven until the part was replaced.

Gen 32001–2006Safety-criticalCommunity consensus

Do not driveNo lo maneje

Safety notice — Brakes.

This affects a safety-critical system. Reference material only: for safety-critical work, consult a qualified mechanic.

Esto afecta un sistema crítico para la seguridad. Material de referencia únicamente: en trabajos críticos para la seguridad, consulte a un mecánico calificado.

Community consensus. This entry is not backed by factory documentation — treat its values and steps as a starting point, not as if they came from the factory manual.

Consenso de la comunidad. Esta entrada no se apoya en documentación de fábrica — tome los valores y los pasos como punto de partida, no como si vinieran del manual de fábrica.

Symptoms

A chirp, honk or gobbling noise from the left of the dash each time you use the brake
Brake and ABS warning lights together, often with a buzzer
The pedal travels much further than it used to, sometimes to the floor
The first stop after the truck has sat is unassisted, then normal assistance returns

Likely causes

The accumulator has leaked its nitrogen charge and no longer stores pressure
The hydraulic pump in the brake unit is failing
The hydraulic booster unit is leaking internally and cannot hold pressure

Diagnostic steps

With the engine running, press and release the pedal several times and listen at the left of the dash panelPoints toThe accumulator has leaked its nitrogen charge and no longer stores pressure
After the truck has sat for a few hours, note whether the very first brake application is unassistedPoints toThe accumulator has leaked its nitrogen charge and no longer stores pressure
Check the brake fluid level, then inspect the booster unit and its fittings for damp spotsPoints toThe hydraulic booster unit is leaking internally and cannot hold pressure
Have the braking system read with a scan tool and the hydraulic unit tested by a shopPoints toThe hydraulic pump in the brake unit is failing · The hydraulic booster unit is leaking internally and cannot hold pressure

Fix paths

Check the VIN and build date against the factory campaign first

$Difficulty 1/5

If the truck is inside the recall population the remedy is the manufacturer's to pay for. Owners report the cut-off is a build date rather than a model year, so ask about both. It costs nothing, and the answer decides which of the paths below you are on.

Replace the accumulator alone

$$–$$$Difficulty 3/5

The accumulator is sold separately from the booster it bolts to. On the later trucks the supplier's listing splits it two ways — a large silver cylinder for those with traction control, a smaller round part for those without — and that listing covers the last four model years only, so do not carry the split back to an earlier truck without checking. Confirm the part against your own VIN before ordering. The system has to be bled afterwards.

Partsgen3-brake-booster-accumulator

Replace the hydraulic booster unit

$$$–$$$$Difficulty 4/5

The honest answer when the pump or the unit itself is at fault rather than the accumulator, and the expensive one. Have a shop confirm which before you buy anything.

Partsgen3-hydraulic-brake-booster