Parts for your 2015 Mitsubishi Asx-Brake booster

2015 Mitsubishi ASX Brake Booster: What It Does and How to Look After It

Based on Mitsubishi Motors service information for the 2010–2016 ASX/RVR/Outlander Sport (Group 35A – Brakes), the 2015 ASX is factory‑fitted with a vacuum‑type power brake unit (brake booster). The Mitsubishi ASA Electronic Parts Catalogue and mainstream workshop databases (e.g., Autodata/ALLDATA) also list a brake booster assembly, one‑way check valve and vacuum hose for this model, confirming the booster is relevant and used on the 2015 Mitsubishi ASX.

On the 2015 Mitsubishi ASX, the brake booster’s job is to make stopping easier and safer by using engine vacuum to multiply the force from the driver’s foot. It sits on the firewall between the brake pedal and the master cylinder. Petrol ASX models draw vacuum from the intake manifold, while diesel variants use a dedicated vacuum pump to feed the booster. Either way, the driver gets a firm, predictable pedal without needing to stomp on it.

There’s no set replacement interval for a booster, it’s a fit‑and‑forget part until symptoms appear. Typical red flags include a hard brake pedal, longer stopping distances, a constant hissing from the dash area, or engine idle changing when the brake is pressed. Sometimes the one‑way check valve or the vacuum hose perishes before the booster itself, so it pays to rule those out first.

As part of regular servicing, it’s smart to:

• Inspect the booster vacuum hose, grommet and check valve for cracks, oil swelling or loose fits.
• Do a quick driveway test: with the engine off, pump the pedal until firm, hold it, then start the engine. The pedal should sink slightly as vacuum assist kicks in. If it doesn’t, there’s a vacuum or booster issue.
• Check for brake fluid at the rear of the master cylinder. A leaking rear seal can let fluid into the booster, damaging the diaphragm, in that case, both master cylinder and booster may need attention.

When replacement is necessary, a technician will typically unbolt the master cylinder and move it aside, disconnect the pedal clevis under the dash, remove the booster mounting nuts, and swap in the new unit. Fresh gaskets, a new clevis clip, and correct pedal free‑play adjustment are important. If brake lines are opened, the system must be bled. On diesel ASX models, verifying the vacuum pump output is also worthwhile. There’s no coding required, but torque specs and pedal height checks matter, so having the job done by a qualified mechanic is the safest bet.

Popular questions

How can an owner tell if the 2015 Mitsubishi ASX brake booster is failing?

Look for a noticeably harder brake pedal, increased stopping distances, or a steady hissing noise near the dash when pressing the pedal. Another giveaway is the pedal not dropping slightly when the engine is started after being pumped firm with the engine off.

Changes in idle speed when braking can also point to a vacuum leak. Before blaming the booster, check the vacuum hose and the check valve, as these smaller items often fail first.

Do diesel 2015 ASX models use a different vacuum source for the brake booster?

Yes. Petrol ASX models use intake manifold vacuum, while the diesel models rely on a dedicated vacuum pump to supply the booster. If braking effort suddenly increases on a diesel, it’s worth testing pump output and the hose/valve before replacing the booster.

Is it safe to drive a 2015 ASX if the brake booster has failed?

It will still stop, but pedal effort skyrockets and stopping distances grow, which isn’t safe in normal traffic. It’s best to organise inspection and repair promptly and avoid driving if the pedal is extremely hard or braking feels unpredictable.