How much does a Land Rover Discovery D300 engine replacement cost in the UK?

A reconditioned AJ20D6 engine typically costs £5,000–£7,500 supply only, with the same engine used across the Discovery D5, Defender L663, and modern Range Rover / Range Rover Sport ranges. Fitting adds £1,100–£1,900. Use our calculator for a figure specific to your vehicle.

Is the Discovery D300 engine reliable?

The AJ20D6 straight-six Ingenium diesel is JLR's most refined 3.0 diesel yet — a genuine step forward from the 306DT V6. It's rated ★★★★☆ based on current data, but as a modern Euro 6d engine, it demands the right servicing and driving patterns. AdBlue and DPF maintenance are the main areas requiring attention.

What are the common problems with the Discovery D300?

DPF/EGR clogging, AdBlue system failures (NOx sensors, AdBlue injector), and oil dilution from interrupted DPF regenerations are the most common issues. No catastrophic design flaws have emerged on the AJ20D6 to date.

Is it worth replacing a Discovery D300 engine, or should I scrap the car?

Against a £25,000+ Discovery D300, a £6,200 recon engine is a manageable 25% of the vehicle's value — worth it. Given the Discovery's strong retained value, replacement is almost always viable. Scrap only if the vehicle has suffered catastrophic damage well beyond the engine.

How do I find my Discovery's engine code?

For the D300, the engine code is AJ20D6 — it's on the VIN plate and vehicle documentation. The D300 badge signifies the 3.0-litre six-cylinder diesel. If you're unsure, tell us your registration date and we'll confirm it for free.

Can I repair the AJ20D6's AdBlue system, or does it need replacement?

Yes — most AdBlue system issues on the AJ20D6 are repairable. NOx sensors and the AdBlue injector are the usual culprits, with repairs typically costing £500–£1,500. If your countdown has started, do not ignore it — get it inspected immediately.

Land Rover Discovery D3002021–present3.0 AJ20D6

Land Rover Discovery D300 Engine Replacement — Compare Prices & Get Quotes

Get quotes today from trusted UK Land Rover Discovery D300 specialists. Compare reconditioned, rebuilt and used AJ20D6 engines — supply & fit available nationwide.

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12-Month Warranty

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Supply & Fit Available

12-Month Warranty

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Discovery D300 Engines — from £4,500 to £8,000Code: AJ20D6

Discovery D300 Engines — from £4,500 to £8,000· Code: AJ20D6

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

The DISCOVERY D300 THROUGH TIME — Era Map

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

The D300's sole engine — JLR's 3.0 straight-six Ingenium, replacing the 306DT V6 in the facelifted Discovery.

GenerationYearsEngine CodeReliabilityRecon CostEra Note

D5 (facelift) BMW 320d D5 (facelift)

2021–presentAJ20D6 (3.0 6-cylinder Ingenium diesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,500–£7,500 [EM-QUOTE]The D300's sole engine — JLR's 3.0 straight-six Ingenium, replacing the 306DT V6 in the facelifted Discovery.

Why use this era map?

Every cost guide, reliability rating and engine code on this page is aligned to the data above. This keeps everything consistent and trustworthy.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Land Rover Discovery D300 Engine Replacement Costs

Supply Only£5,000–£7,500

Fitted (Indie)£6,100–£8,900

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£4,500–£6,500£5,400–£7,8003–6 monthsBudget priority; vehicle under £15,000

Reconditioned Engine£5,000–£7,500£6,100–£8,90012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£6,000–£8,000£7,100–£9,40012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer New£9,000–£13,000£10,500–£15,00024–36 monthsInsurance jobs, warranty claims

Labour estimate: Fitting a Discovery D300 engine typically takes 12–16 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer).

Common Problems

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Discovery D300 — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Discovery D300 — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseDPF/EGR clogging (AJ20D6)✅ Yes£400–£1,200Preventative — catches the issue before turbo/injector damage occursAdBlue system failure (AJ20D6)✅ Yes£500–£1,500Straightforward sensor/pump replacement if caught earlyOil dilution from failed DPF regen⚠️ Depends£100–£300If caught before bearing damage; if not, engine replacement requiredCrankshaft bearing failure❌ Usually NoEngine replacementNot a common AJ20D6 failure; if it occurs, replacement is the only optionTurbocharger failure✅ Yes£1,500–£3,500Repairable by specialists; do not drive with boost issues

Buying This Discovery D300? Check These First

Buy If

Full Land Rover service history with documented oil-change intervals
Evidence of regular motorway driving (to clear the DPF)
AdBlue system health check passed within the last 12 months
Post-2022 build with any early AdBlue software updates applied

Avoid If

Service history shows only urban driving patterns (DPF risk)
Oil level is visibly above the max mark on the dipstick
No record of AdBlue system maintenance or sensor replacements
Engine warning light present with no diagnosis documentation

Closing Verdict

The Discovery D300's AJ20D6 is JLR's most refined 3.0 diesel yet — a genuine step forward from the 306DT V6. But it's a modern Euro 6d engine with the complexity that entails. Buy on service history and proof of motorway use, not on a clean MOT alone. If you're replacing, a reconditioned unit with a 12-month warranty is the sweet spot.

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12-Month Warranty as Standard

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Thousands of 320d Owners Helped

Buying Checklist

Before you buy a used Land Rover Discovery D300 (or before you commit to an engine replacement), check these:

Cold Start — Listen for any unusual rattle or diesel knock; the AJ20D6 should start smoothly and quietly

Service History — Including which engine era (AJ20D6 is the only D300 engine — verify this before purchase)

Oil Level Check — Is the oil above the max mark? This indicates potential diesel contamination from interrupted DPF regens

AdBlue System — Check the AdBlue countdown; any warnings? NOx sensors are a known weak point

DPF Regeneration — Has the vehicle had regular motorway runs? Short journeys accelerate DPF wear on this engine

Oil Consumption — Does it use more than 1L per 5,000 miles? If so, investigate

Engine Warning Light — Have codes been read? Any unresolved issues with the emissions system?

MOT History — Check for emissions-related failures; repeated advisories on the DPF are a red flag

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Engine Codes

AJ20D6

Years2021–present

Power300 bhp / 650 Nm

2025 Enquiries— (pattern data)

Avg. Recon Cost£5,000–£7,500 [EM-QUOTE]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

AJ20D62021–present300 bhp / 650 Nm— (pattern data)£5,000–£7,500 [EM-QUOTE]

Technical Specs

AJ20D6

Displacement2,999cc

Cylinders6-cylinder inline (straight-six)

Compression Ratio15.5:1

Fuel SystemCommon-rail direct injection (2,500 bar)

TurbochargerTwin sequential turbo (MHI / Garrett)

Market Intelligence

Most Common Failure

AdBlue system failures (NOx sensors, AdBlue pump) — approximately 35% of D300 enquiries

[PATTERN DATA]

Average Enquiry Mileage

58,000

miles

[PATTERN DATA]

Average Replacement Cost

£6,200

reconditioned, supply only

[EM-QUOTE]

Most Requested Engine Code

AJ20D6

[EM-VERIFIED]

Peak Enquiry Season

Winter — AdBlue and DPF issues worsen in colder conditions

[PATTERN DATA]

Regional Demand

South East24%

Midlands18%

North West15%

PATTERN DATA

Regional Demand Breakdown

24%South East

15%North West

FAQ

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty — always confirm terms with your chosen supplier.

Find the best Land Rover Discovery D300 engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

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100% Free

No hidden fees

No Obligation

Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available