IsItAGoodCar
Reliability Guide

Common Problems with the
2018 Audi A8 Mk4 (D5)

The launch year brought Audi's most complex flagship with dual-touchscreen MMI and 48V mild-hybrid as standard. Early 2018-2021 cars carry a known BSG failure risk — the recall (27BQ) is essential and should be verified before purchase.

What changed for 2018

  • •Launch with 3.0 TFSI and 4.0 TDI engines
  • •Standard 48V mild-hybrid system
  • •Dual-touchscreen MMI with haptic feedback

Common MOT watch-outs

  • !48V BSG failure leaving car stranded
  • !Air suspension strut leaks
  • !Dual MMI screen freezes and reboots
4
Known Issues
3
Serious
1
Moderate
0
Minor

All Known Issues

48V Belt-Starter Generator (BSG) Failure

SeriousElectrics & Electronics

The Continental BSG power transistors overheat and fail, causing the 48V system to shut down and eventually leaving the car stranded.

Est. Repair Cost: £0 (recall) – £2,500
Warning Signs:

Multiple electrical system warnings, Start-stop inactive, Car immobilised after standing

What to Inspect:
  • Verify service campaign 27BQ has been completed via VIN
  • Check for electrical system warnings on startup
  • Ask for BSG replacement invoice
Verified by IsItAGoodCar Research TeamUpdated

Air Suspension Strut Leaks

SeriousSuspension & Chassis

The standard adaptive air suspension develops leaks over time, causing uneven ride height and expensive compressor replacement.

Est. Repair Cost: £800–£3,000
Warning Signs:

Car sitting low on one corner, Compressor running constantly, Level-control warning

What to Inspect:
  • Check ride height before engine start
  • Cycle through height settings
  • Listen for compressor strain
Verified by IsItAGoodCar Research TeamUpdated

TDI SCR / AdBlue System Faults

SeriousExhaust & Emissions

Diesel versions with SCR can develop dosing, heater or NOx sensor faults. A system fault may lead to a no-restart countdown even with sufficient AdBlue; diagnosis should distinguish fluid level from component failure.

Warning Signs:

AdBlue system warning, No-restart countdown

What to Inspect:
  • Check warning history and emissions repair invoices
  • Request a diagnostic check of dosing pressure, heater operation and NOx readings
Verified by IsItAGoodCar Research TeamUpdated

Dual-Touchscreen MMI Freezes

ModerateElectrics & Electronics

Both the upper and lower MMI screens can freeze, go black, or reboot, affecting navigation, climate and seat controls.

Est. Repair Cost: £0–£2,500
Warning Signs:

Upper screen going black, Lower climate screen unresponsive, Spontaneous system reboots

What to Inspect:
  • Test both screens extensively
  • Try a 15-second power button reset
  • Check for pending software updates
Verified by IsItAGoodCar Research Team

Buying Tips for 2018 Audi A8 Mk4 (D5)

  • Verify service campaign 27BQ has been completed via VIN before viewing
  • Check both upper and lower MMI screens for lag
  • Air suspension must sit level after standing overnight
20172019–2021
Check a 2018 Audi A8 Mk4 (D5) by Registration