Porsche 911 MOT Failures
An analysis of 128,976 real DVSA MOT tests on the Porsche 911 — what fails, how often, and how that compares to every other car on UK roads. Generations covered: 996 (1997–2005), 997 (2004–2012), 930 (1975–1989), 964 (1989–1994), 993 (1994–1998), 991 (2011–2019), 992 (2019–2024).
Where the Porsche 911 fails its MOT
The single biggest MOT failure point on the Porsche 911 is light unit fault — this model is 26 times more likely to fail on this item than the average car on UK roads. That makes it a significant weak point for anyone buying or owning this model. Across 128,976 MOT tests, 2.55% of all Porsche 911 tests recorded this as a failure.
Lighting faults are usually straightforward to fix (bulbs, connectors, earth points) but can indicate deeper wiring issues on older cars. Check all lights including fog lamps, number plate lights, and dashboard warning lights.
Other notable weak points include emissions failure (126x the fleet average), obligatory rear fog lamp missing, or a front or... (10x the fleet average), wheel bearings worn (37x the fleet average), and suspension component damaged or corroded (26x the fleet average). These ratios compare the Porsche 911's failure rate on each item against the national average for all cars tested — a ratio of 10x means this model fails ten times more often than a typical car.
The failures span 4 categories: Lights & Electrics, Exhaust & Emissions, Suspension, Tyres. If you're inspecting a Porsche 911 before purchase, these are the areas to focus on — and if any have been flagged as advisories on a previous MOT, they're likely to become failures in the near future.
How failures change with mileage
The Porsche 911's weak points shift as the car covers more miles. Understanding these patterns helps you know what to expect — and what to budget for — at each stage of ownership.
Under 60,000 miles
At this mileage, most failures are either design-related or caused by age rather than wear. Components like bushes and drop links may not have been replaced yet, and original-fit parts can deteriorate even on low-mileage cars that spend a lot of time sitting.
For the Porsche 911 specifically, the DVSA data shows the most common failures at this mileage are tyre valve seriously damaged or misaligned (35x the average) and suspension component damaged or corroded (26x). wheel bearings worn (25x) and anti-roll bar links worn (20x) also appear frequently.
60,000 to 100,000 miles
This is where routine wear items start to show up. Brake components, tyres, and exhaust parts have done serious work by this point. Cars that have been well serviced will show fewer of these failures — this mileage band is where good maintenance really separates the well-kept from the neglected.
For the Porsche 911 specifically, the DVSA data shows the most common failures at this mileage are light unit fault (21x the average) and emissions failure (14x). wiper fault (14x) and suspension ball joints worn (11x) also appear frequently.
Over 100,000 miles
High-mileage cars accumulate failures across multiple systems. The key question isn't whether things will need doing — they will — but whether the car has been maintained well enough to keep on top of them. Look for a consistent service history and recent MOT passes with minimal advisories.
For the Porsche 911 specifically, the DVSA data shows the most common failures at this mileage are emissions failure (101x the average) and light unit fault (26x). tyre valve seriously damaged or misaligned (17x) and obligatory rear fog lamp missing, or a front or... (7.8x) also appear frequently.
The shift from tyre valve seriously damaged or misaligned at lower mileages to emissions failure at higher mileages is typical — early failures tend to be design or factory-related, while high-mileage failures reflect accumulated mechanical wear. A car that's been well maintained will usually dodge the worst of both.
Known issues beyond the MOT
An MOT only tests roadworthiness at a single point in time — it won't catch developing faults, intermittent problems, or issues that haven't yet reached the failure threshold. These are the issues that Porsche 911 specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.
IMS bearing failure (996) Dangerous
The intermediate shaft (IMS) bearing supports the shaft that drives the camshafts in M96 flat-six engines. Affects 996, 997.
Bore scoring (less common than 997.1) (997) Dangerous
Cylinder bore scoring occurs when the piston rings lose sealing ability and allow metal-to-metal contact between pistons and cylinder walls. Affects 997, 991.
Coolant pipe failure (996 Mezger) Dangerous
The Mezger flat-six engine in GT3 and Turbo models uses different coolant routing than the M96, with additional cooling pipes that can corrode and fail. Affects 996, 997; typical independent garage repair cost is £400–£800.
Cylinder bore scoring (996) Dangerous
The M96 flat-six cylinder bores can score due to insufficient lubrication, particularly on the cylinder 6 bore which runs hotter and receives less oil flow. Affects 996.
For the complete picture — including repair costs across independent, specialist, and dealer garages — see the full Porsche 911 common problems breakdown.
What to check before buying a Porsche 911
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Porsche 911:
Lights & Electrics — check for light unit fault, obligatory rear fog lamp missing, or a front or..., headlight fault. Exhaust & Emissions — check for emissions failure. Suspension — check for wheel bearings worn, suspension component damaged or corroded, anti-roll bar links worn.
Beyond the MOT items, ask specifically about ims bearing failure and bore scoring. These won't show up on a standard MOT but can be expensive to fix — A specialist pre-purchase inspection is worth the investment on this model.
Always check the car's full MOT history for patterns — recurring advisories often become failures within 12 months. And verify the service history to confirm maintenance has been kept up to schedule. Enter any reg into our free car check to see the complete picture.
Looking at a specific Porsche 911?
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Porsche 911 MOT FAQs
What are the most common MOT failures on a Porsche 911?
Based on 128,976 DVSA MOT tests, the most common failure is light unit fault — at 26x the national fleet average. Other frequent failures include emissions failure and obligatory rear fog lamp missing, or a front or....
Is the Porsche 911 reliable based on MOT data?
The Porsche 911 has 16 MOT failure categories above the fleet average. Specialists also flag ims bearing failure as a concern. A pre-purchase inspection and service history check are recommended.
What MOT failures should I expect at high mileage?
Above 100,000 miles, the Porsche 911 most commonly fails on emissions failure and light unit fault. Under 60,000 miles, the main issues are tyre valve seriously damaged or misaligned and suspension component damaged or corroded.
How do I check a Porsche 911's MOT history?
Enter the registration number into our free car check above. You'll see every MOT test result, advisories and failures, mileage readings, write-off status, and finance checks.
MOT failure data sourced from DVSA bulk test records via data.gov.uk. Ratios compare this model's failure rate against the national fleet average. Known issues sourced from manufacturer bulletins, specialist workshops, and verified owner reports.