IsItAGoodCar
Reliability Guide

Common Problems with the
2018 Mazda 3 (BM/BN)

We've identified 4 known issues that can affect the 2018 Mazda 3 (BM/BN). 1 of these are serious faults that could be expensive to repair.

4
Known Issues
1
Serious
1
Moderate
2
Minor

All Known Issues

2.2 SkyActiv-D DPF and Oil Dilution

SeriousEngine

Short-trip town use causes frequent interrupted DPF regenerations on the 2.2 diesel, allowing diesel to dilute the engine oil. This can accelerate timing-chain, turbo and bottom-end wear. The problem is severe enough to warrant regular oil-level checks between services.

Est. Repair Cost: £300–£4,000
Warning Signs:

Rising oil level on dipstick, DPF warning light, Limp mode after town use

What to Inspect:
  • Check the dipstick level carefully; oil above the maximum mark is a red flag
  • Ask what kind of journeys the car typically does
  • Look for invoices for DPF cleaning or turbo work
Verified by IsItAGoodCar Research Team

Brake Disc Warping

ModerateBrakes

The front brake discs on BM/BN Mazda3s are prone to developing run-out and thickness variation, causing a judder through the steering wheel and brake pedal during braking. This is more common on cars used heavily in town with frequent low-speed stops.

Est. Repair Cost: £150–£350 per axle
Warning Signs:

Vibration through steering wheel under braking, Pulsing brake pedal, Uneven pad wear

What to Inspect:
  • Test brake feel from moderate speed
  • Inspect front discs for scoring or a visible lip
  • Check MOT history for brake advisories
Verified by IsItAGoodCar Research Team

Folding Mirror Motor Failure

MinorElectrics & Electronics

The plastic gears in the mirror motor strip, causing the mirrors to get stuck or make a clicking noise.

Est. Repair Cost: £150–£300 per mirror
Warning Signs:

Mirror won't fold/unfold, Grinding noise

What to Inspect:
  • Fold and unfold the mirrors several times using the door switch
Verified by IsItAGoodCar Research Team

12V Battery Premature Failure

MinorElectrics & Electronics

The Mazda3 BM/BN is known for draining its 12V battery faster than expected, particularly on models with the i-stop (start-stop) system. Owners frequently report needing replacement batteries after just two to three years.

Est. Repair Cost: £100–£180
Warning Signs:

Slow cranking on cold mornings, Stop/start system not engaging, Battery warning light

What to Inspect:
  • Check the battery age and condition
  • Verify the stop/start system activates during the test drive
  • Ask when the battery was last replaced
Verified by IsItAGoodCar Research Team

Buying Tips for 2018 Mazda 3 (BM/BN)

  • ✓Prefer the 2.0 SkyActiv-G petrol over any diesel.
  • ✓Check the infotainment screen for spider-web cracking (delamination).
  • ✓Test the folding mirrors multiple times.
20172019
Check a 2018 Mazda 3 (BM/BN) by Registration