Mercedes Benz Gl MOT Failures

An analysis of 20,833 real DVSA MOT tests on the Mercedes Benz Gl — what fails, how often, and how that compares to every other car on UK roads. Generations covered: X164 (2006–2012), X166 (2012–2019).

Where the Mercedes Benz Gl fails its MOT

The single biggest MOT failure point on the Mercedes Benz Gl is reflector defective or damaged by up to 50% of ... — this model is 16 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 20,833 MOT tests, 1.16% of all Mercedes Benz Gl 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 brake pedal anti-slip provision missing, loose ... (10x the fleet average), cable damaged or knotted (22x the fleet average), headlight fault (46x the fleet average), and subframe bushes or mounts worn (12x the fleet average). These ratios compare the Mercedes Benz Gl'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, Brakes, Suspension, Exhaust & Emissions. If you're inspecting a Mercedes Benz Gl 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 Mercedes Benz Gl'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 Mercedes Benz Gl specifically, the DVSA data shows the most common failures at this mileage are reflector defective or damaged by up to 50% of ... (12x the average) and brake pedal anti-slip provision missing, loose ... (10x). emissions failure (6.2x) and emissions failure 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 Mercedes Benz Gl specifically, the DVSA data shows the most common failures at this mileage are headlight fault (29x the average) and reflector defective or damaged by up to 50% of ... (11x). brake lining or pad worn down to wear indicator (6.5x) and brake pedal anti-slip provision missing, loose ... (5.5x) 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 Mercedes Benz Gl specifically, the DVSA data shows the most common failures at this mileage are headlight fault (46x the average) and subframe bushes or mounts worn (12x). cable damaged or knotted (11x) and reflector defective or damaged by up to 50% of ... (8.8x) also appear frequently.

The shift from reflector defective or damaged by up to 50% of ... at lower mileages to headlight fault 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 Mercedes Benz Gl specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.

Brake pipe corrosion (X164) Dangerous

Steel brake lines on the X164 GL generation corrode extensively due to road salt exposure and the vehicle's ground clearance exposing lines to spray. Affects X164; typical independent garage repair cost is £400–£600.

CV joint boot deterioration (X164/X166)

The constant velocity joint boots on GL models deteriorate at a higher rate than the fleet average, particularly on 3.0L diesel variants. Affects X164, X166; typical independent garage repair cost is £150–£250.

Engine management light - diesel emissions system (X164/X166)

This typically relates to the complex diesel emissions system including EGR valve carbon build-up, DPF regeneration issues, or AdBlue system faults on later models. Affects X164, X166; typical independent garage repair cost is £200–£800.

Rear shock absorber failure (X164)

The 4.0L diesel X164 GL models show elevated rates of rear shock absorber failure, typically manifesting as oil leakage or complete loss of damping function. Affects X164; typical independent garage repair cost is £200–£400.

For the complete picture — including repair costs across independent, specialist, and dealer garages — see the full Mercedes Benz Gl common problems breakdown.

What to check before buying a Mercedes Benz Gl

Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Mercedes Benz Gl:

Lights & Electrics — check for reflector defective or damaged by up to 50% of ..., headlight fault. Brakes — check for brake pedal anti-slip provision missing, loose ..., cable damaged or knotted, brake lining or pad worn down to wear indicator.

Beyond the MOT items, ask specifically about brake pipe corrosion and cv joint boot deterioration. These won't show up on a standard MOT but can be expensive to fix — repairs start from £400. 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.

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.