Full-size seven-seat luxury — prepare for running costs
The Mercedes GL-Class (later renamed GLS) is a full-size luxury seven-seat SUV that rivals the Range Rover and BMW X7. Heavy depreciation from six-figure new prices creates tempting used bargains, but the sheer complexity of the air suspension, electronics and V6/V8 powertrains means ownership costs can escalate rapidly without meticulous maintenance history.
We track 5 known issues across the Mercedes-Benz GL range, including 1 rated as safety-critical. Knowing which variants and configurations to approach with caution can save you from expensive surprises after purchase.
Found a Mercedes-Benz GL? Enter the reg to see which of our 5 known issues apply to that exact car, plus full MOT history and mileage checks.
X164 (2006–2012) — Petrol options included the 5.5L V8, with 3.0L V6 CDI, 4.0L V8 CDI on the diesel side. Our database flags 5 known issues on this generation, 1 of which are rated as safety-critical. The most significant concern is Brake pipe corrosion (£400–£600 to address).
X166 (2012–2019) — Petrol options included the 5.5L V8, with 3.0L V6 CDI on the diesel side. 3 known issues affect this generation, none rated as critical. The most significant concern is CV joint boot deterioration (£150–£250 to address).
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. The 4.0L diesel variants show particularly high failure rates at MOT testing, with corrosion severe enough to compromise braking safety. This affects the high-pressure steel lines running along the chassis, not the flexible rubber sections at the wheels. Later X166 models use improved corrosion protection.
Corroded brake lines can rupture without warning, causing complete brake failure and a serious safety hazard. Professional brake line replacement costs £400-£800 depending on how many sections need renewal. The vehicle is unsafe to drive if brake line corrosion is advanced.
Check brake disc condition for lipping or scoring. Test braking at moderate speed for pulling to one side or vibration through the steering wheel. Review MOT advisories for brake-related items.
The constant velocity joint boots on GL models deteriorate at a higher rate than the fleet average, particularly on 3.0L diesel variants. These rubber boots protect the CV joints from dirt and moisture while containing lubricating grease. The heavy weight of GL vehicles and large wheel travel in off-road use accelerates boot wear. Boot failure allows grease to escape and contaminants to enter, eventually destroying the expensive CV joint itself.
Failed boots allow grease to escape and dirt to contaminate the CV joint, leading to clicking noises and eventual joint failure. Boot replacement costs £150-£300 per side if caught early. If the joint is damaged by contamination, full driveshaft replacement costs £400-£700 per side.
Listen for clunking or vibration from underneath when pulling away or changing direction. Check for play in the driveshafts by rocking the car in gear with the handbrake on. Worn CV boots are a telltale sign — look for grease splatter around the inner wheel arch.
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. The heavy weight and frequent urban use of these vehicles exacerbates diesel emissions problems.
Engine management lights typically indicate emissions system faults requiring diagnostic investigation. Common issues include EGR valve cleaning (£200-£400), DPF replacement (£1,500-£2,500), or AdBlue system repairs (£300-£800). The vehicle may enter limp mode limiting performance until repaired.
Check for any engine warning lights on the dashboard. Ask about the car's MOT emissions history — repeated failures suggest underlying issues. A pre-purchase diagnostic scan is especially worthwhile to check for stored emissions fault codes.
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. The heavy weight of these vehicles and the complexity of the air suspension system on higher trim levels contributes to premature shock wear. Standard steel spring models use conventional dampers while air suspension variants have more complex units integrated with air springs.
Failed shock absorbers reduce ride quality, vehicle stability, and tyre life. Standard shock replacement costs £200-£400 per side. Air suspension units cost £600-£1,200 per side. The vehicle remains safe to drive but handling and comfort are compromised.
Listen for knocking, clunking or rattling over bumps during the test drive. Inspect the underside for corroded or cracked suspension components. Check the MOT history for suspension-related advisories, which often predict future failures.
GL models show an unusually high rate of brake pedal anti-slip rubber pad deterioration, affecting primarily the 3.0L diesel variants in higher mileage ranges. The rubber pad that provides grip for the driver's foot wears smooth or comes loose, creating a potential safety issue where the foot might slip off the brake pedal. This is a simple but important safety component that must be replaced when worn.
A worn or missing brake pedal pad can cause foot slippage during emergency braking, potentially affecting stopping ability. Replacement is inexpensive at £10-£30 but essential for safe pedal operation. The vehicle remains roadworthy but should be repaired promptly.
Check brake disc condition for lipping or scoring. Test braking at moderate speed for pulling to one side or vibration through the steering wheel. Review MOT advisories for brake-related items.
For the full breakdown of all 5 tracked issues with repair costs, see the Mercedes-Benz GL common problems page.
Based on 19k real DVSA MOT tests, the Mercedes-Benz GL fails more often than average on several items. The biggest outlier is headlight fault at 46x the fleet average, followed by cable damaged or knotted (22x).
When viewing a specific car, check its MOT history for recurring advisories in these categories. See the full Mercedes-Benz GL MOT failure breakdown for data at every mileage point.
Routine servicing (oil and filter change every 16k miles) typically costs £180–£280 at an independent garage.
The bigger-ticket items to budget for include coolant flush (£200–£350), automatic transmission fluid (£350–£500).
See the full Mercedes-Benz GL service schedule for every interval and cost breakdown.
The Mercedes-Benz GL has some well-documented weak points, including 1 safety-critical issue that demand careful checking. The right example, properly maintained, can still be a sound purchase — but cutting corners on the pre-purchase inspection is not advisable. 2012-2015 X166 generation for the best blend of modern refinement and proven reliability; diesel GL350 is the sensible choice
Before committing, check the car's full MOT history, verify the service record is complete, and if possible arrange a specialist inspection. Enter any registration into our free report to see the complete picture.
Get Car Wise maintains a database of known mechanical issues for every popular car on UK roads, tracking the faults that owners, specialists and DVSA data reveal.
When you run a report on a specific Mercedes-Benz GL, we cross-reference the exact variant, engine and age against our database of 5 known issues. Combined with full MOT history analysis, mileage verification and DVLA data, you get a complete picture before viewing.
Enter the registration for MOT history, mileage verification, known faults for that exact variant, and a Get Car Wise Score.
This guide was compiled from independent expert reviews, DVSA MOT data, specialist workshops and our own database of 5 known Mercedes-Benz GL issues. We are not affiliated with any source listed.