Popular premium compact SUV combining Mercedes comfort with practical diesel efficiency. The OM651 engine is generally reliable but has known issues: early models (2015-2016) used problematic Delphi piezo injectors (later replaced under recall), timing chain tensioner can fail causing cold-start rattle around 80,000-120,000 km, and DPF clogging is common with short-trip urban driving. The 9G-Tronic transmission is smooth but can develop mechatronics faults. AdBlue system NOx sensor failures are frequent. Air suspension (if equipped) is less reliable than steel springs. Models from 2019 onwards show better overall reliability. Right-hand-drive models suffer from a crabbing/steering geometry issue.
The OM651 engine uses a simplex (single-row) timing chain with a tensioner that has a release valve. Over time, this valve weakens and allows oil pressure to bleed off overnight. This causes a rattling noise lasting 1-30 seconds on cold starts, typically appearing between 60,000-100,000 km. If ignored, the chain can skip timing and cause catastrophic valve/piston contact. Full replacement requires new chain, guides, tensioner, and sprockets. Mercedes updated the tensioner part but the fundamental simplex design remains a weak point. The newer OM654 diesel uses a more robust duplex chain.
Short urban trips prevent regeneration, causing soot buildup · more· less
The GLC 220d uses a Euro 6 SCR system with DPF. Short trips with frequent cold starts prevent the exhaust from reaching regeneration temperature (typically achieved during highway driving). If driven predominantly in city traffic, the DPF will clog. Early warning signs include amber filter warning light and reduced power. The DPF pressure sensor can also fail, causing premature clogging warnings. DPF cleaning costs €600-900, but if damage has occurred, full replacement runs €1,200-2,800. The filter should be cleaned or replaced every 75,000-100,000 km regardless. Regular highway drives help prevent issues.
Early Delphi piezo injectors highly problematic, later replaced with magnetic type · more· less
Early GLC 220d models (2015-2016) were equipped with problematic Delphi piezo injectors that had an extremely high failure rate, generally occurring beyond 50,000 km. Mercedes spent approximately €500 million repairing 300,000 affected engines worldwide and eventually discontinued piezo injectors entirely, replacing them with magnetic solenoid injectors from mid-2012 onwards. Symptoms include rough running, vibrations during acceleration, check engine light, and limp mode. If your GLC is from 2015-2016, verify whether the recall (service action 07921) was completed and injectors replaced with magnetic type. If not, budget for this repair. Later models with magnetic injectors are much more reliable.
AdBlue/NOx sensor failure€700 - €2,100
NOx sensors fail, causing "engine start not possible" countdown warnings · more· less
The GLC 220d uses an SCR (Selective Catalytic Reduction) system with AdBlue injection. Common issues include NOx sensor failures (most common), blocked AdBlue injector, and AdBlue tank faults. Warning messages like "Eng start not possible in xxx kilometres" or "Unable to measure AdBlue level" indicate system malfunction. NOx sensor replacement costs €700-900 per sensor (there are two: upstream and downstream). If the AdBlue injector is clogged, replacement runs €400-600. AdBlue tank replacement (less common) costs €1,200-1,400. The system can only be reset 3 times before requiring ECU recalibration. Some owners report increased AdBlue consumption after software updates.
TCM conductor plate fails, causing shifting delays and neutral engagement issues · more· less
The 9G-Tronic transmission is generally reliable but can develop issues with the mechatronics unit (TCM conductor plate). Common symptoms include jerky shifts at low speeds, hesitation when engaging drive, transmission auto-selecting neutral after warmup, and being stuck in 3rd-5th gear safe mode. The fault typically occurs after the gearbox heats up significantly. Approximately 10-15% of owners report transmission issues within 100,000 miles. Software updates resolve some cases, but failed conductor plate requires replacement. Regular transmission fluid changes every 60,000-80,000 km help prevent issues. Full mechatronics replacement costs €1,500-2,000; if internal clutch damage occurred, full transmission work runs €2,500-3,500.
EGR valve carbon buildup€400 - €900
Valve sticks from carbon deposits, especially with urban driving · more· less
The EGR (Exhaust Gas Recirculation) valve develops carbon buildup that restricts airflow, causing rough idling, check engine light, loss of power, increased fuel consumption, and engine stalling. This is especially common with short-trip urban driving. Symptoms include strong exhaust smell and engine vibrations at idle. Cleaning the EGR valve costs €200-350, but if the valve is seized or severely damaged, replacement runs €400-600 for parts plus 2-3 hours labor. The EGR valve and DPF are directly related - if the EGR isn't working properly, the DPF clogs faster. Check/clean the EGR valve every 50,000 km as preventive maintenance.
Oil cooler seal leak€1,000 - €1,800
OM651 oil cooler seals degrade, causing oil leaks on driver side · more· less
The OM651 engine has a known oil cooler seal leak issue. The oil cooler is integrated into the oil filter housing and tucked on the driver side of the engine block. Original seals were orange rubber that degraded from heat; Mercedes updated to purple Viton seals in 2010 that resist heat better. Symptoms include visible oil leaks and decreasing oil levels. The seals themselves cost about €130-200 including oil filter, but labor is expensive due to poor accessibility - expect 10-15 hours labor at independent shops (€1,000 total) or up to €1,500-1,800 at dealers. Always specify purple Viton seals when replacing. DIY repair takes 2-3 days.
AIRMATIC air suspension leaks (if equipped)€1,200 - €2,500
Air struts develop leaks, rubber bellows crack, compressor overworks · more· less
The GLC offers optional AIRMATIC air suspension which provides excellent comfort but is significantly less reliable than steel springs. Rubber air bellows and seals become brittle and crack over time, typically requiring replacement around 80,000-100,000 km (8-10 years). Symptoms include car sagging (especially rear), hissing sounds, uneven ride height, and compressor running excessively. Single strut replacement costs €1,200-1,900 including labor; compressor replacement runs €650-900. In hot climates, lifespan can be as short as 6 years. If multiple components fail, total repair can exceed €3,000-5,000. Steel spring suspension is much more reliable and costs only €400-600 per corner to repair. Some owners convert from air to coil springs to eliminate ongoing problems.
Brake squeal issue€400 - €800
Factory brake pads squeal at low speeds, especially in cold weather · more· less
This is a well-documented issue affecting GLCs from 2016 onwards. Brakes squeal, screech, or squeak at low speeds (under 10 mph), especially in reverse and cold weather. Mercedes issued technical service bulletins (L142.10-P-064944 and L142.10-P-065927). The original brake pads had straight-ended designs that created harmonic vibrations. Mercedes updated the pad design with rounded/angled ends and new part numbers. Solution: replace pads (and often rotors) with updated parts. Front and rear pad replacement costs €400-600; pads plus rotors runs €600-800. Some dealers perform warranty replacement if pushed. Changing pad material type (ceramic to semi-metallic) can also eliminate squeal.
Steering rack crabbing (RHD models)€600 - €1,200
Right-hand drive models suffer tire skipping/scrubbing at full lock · more· less
This is a design flaw specific to right-hand drive GLC models due to front axle differential positioning. At full steering lock, the steering geometry becomes incorrect, causing front tires to skip/scrub. The issue is worse with larger wheels and low-profile tires, and more pronounced in cold weather. Mercedes acknowledges this and offers modified steering knuckles under warranty (not a recall - must be requested). The knuckle modification was implemented around 2019-2020. AMG models (GLC43, GLC63) cannot be fixed due to different steering rack. Workarounds include proper 4-wheel alignment, tire rotation every 10,000 km, and fitting all-season tires. The fix (steering knuckles plus alignment) costs €600-1,200 at dealers and significantly improves tire wear and handling.
Faulty sensors, infotainment freezes, persistent warning lights · more· less
First-generation GLC (2015-2019) models commonly experience electrical issues including faulty sensors, infotainment system freezes, and persistent warning lights. The COMAND system (early models) and MBUX system (later models) both experience occasional glitches. Most issues are resolved through software updates from Mercedes dealerships. Specific sensor failures (parking sensors, tire pressure sensors, various engine sensors) can cause unpredictable electrical behavior. Some owners report cooling fans randomly cycling when car is off, or instrument cluster going to blank white screen. Most problems are software-related and fixed via updates. Hardware sensor replacement costs €200-400 per sensor. Models from 2019 onwards have better software stability. Always update infotainment firmware during service.
Solid diesel SUV with typical modern diesel complexities
The GLC 220d is a competent premium SUV when properly maintained. The OM651 engine is fundamentally robust, but early piezo injector issues and ongoing timing chain/DPF concerns require attention. The 9G-Tronic transmission is generally reliable. Budget for diesel-specific maintenance (DPF, AdBlue, EGR) and verify piezo injector recall completion on 2015-2016 models. Avoid air suspension if possible. Models from 2019 onwards show improved reliability. Not suited for short-trip urban-only driving due to DPF issues.
Pre-Purchase Inspection Checklist
General checks
Service history
Complete Mercedes dealer or specialist service records essential. Verify annual services and DPF regeneration history.
Tires
Check tread depth, age (date codes), uneven wear (especially on RHD models with crabbing issue). Original run-flats ride harsh; many owners switch to standard tires.
Cold start
Must start engine completely cold. Listen carefully for timing chain rattle in first 30 seconds.
Body condition
Check for accident damage, paint mismatch, panel gaps.
Test drive
Minimum 20-30 minutes including highway speeds to warm transmission and check DPF regeneration behavior.
Specific for this vehicle
Timing chain cold-start rattle test
This is the most critical check. Start engine completely cold and listen for rattling in first 30 seconds. Any rattle indicates chain/tensioner wear requiring immediate attention.
Verify piezo injector recall completed (2015-2016 models)
Contact Mercedes with VIN to confirm service action 07921 was completed. If not, negotiate significant price reduction or walk away.
DPF status and regeneration
Check for amber DPF warning light. Ask about typical driving pattern - if mostly short city trips, DPF is likely problematic. Request DPF pressure reading from diagnostic scan.
AdBlue system check
Verify AdBlue level and range display works correctly. Test for any "AdBlue system fault" messages. Check AdBlue consumption history - excessive consumption indicates sensor issues.
9G-Tronic transmission behavior
Drive for 15+ minutes until transmission is hot. Feel for jerky shifts, hesitation engaging drive, or transmission slipping into neutral. Any issues indicate expensive mechatronics repair.
Oil cooler seal inspection
Look for oil leaks on driver side of engine, especially around oil filter housing. Check oil level - low oil combined with visible leak indicates active cooler seal failure.
Air suspension test (if equipped)
Check for sagging corners, uneven ride height, hissing sounds near wheel wells. Test ride height adjustment functionality. Listen for excessive compressor running.
Brake squeal test
At low speeds (parking lot), test brakes in forward and reverse. Loud squealing indicates original pads need replacing with updated design.
Steering geometry/crabbing (RHD models only)
At low speed in parking lot, turn to full lock and move slowly. Feel for tire skipping/scrubbing. Check if steering knuckle recall/update was completed.
EGR valve function
Check for rough idle, hesitation, or exhaust smell. Request diagnostic scan for EGR-related codes.
Contact Mercedes-Benz with VIN to verify all recalls completed. The piezo injector recall (2015-2016) and intake line assembly extended warranty (2015-2020) are particularly important.
Warranty Status
Factory warranty (4 years / 50,000 miles)Expired on all 2015-2022 models
Intake line assembly warranty extension (MY 2015-2020)15 years / 150,000 miles from new
Mercedes extended warranty (optional)€3,000-4,500 for 3 years
Certified Pre-Owned (CPO) warranty12 months unlimited mileage if available
All 2015-2022 GLC 220d models are outside original factory warranty. Extended warranty is available through Mercedes dealers for €3,000-4,500 covering 3 additional years. Note that extended warranty pricing is most affordable when purchased before factory warranty expires. Certified Pre-Owned vehicles come with 12-month unlimited-mileage warranty after factory warranty expires.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.