{"nhtsa_id":11028267,"type":"service_bulletin","type_name":"Service bulletin","date_added":"2026-02-04","date":"2026-02-02","document_id":"LI01.30-P-072328","mfr_campaign":null,"replaces":null,"component":"ENGINE","mfr_system":null,"summary":"Complaint -Check engine light illuminated. -Engine runs rough. -Poor shifting or jerking when accelerating. -Fault codes stored related to mixture formation, injector quantity adjustment, or misfire. Note: One or more of the above symptoms can occur. It is possible that no fault codes are stored. Cause Leaking valve seat in cylinder head. Remedy -Perform cylinder leakage check as noted in WIS group 01.00. If excessive leakage is found determine if leak is from intake or exhaust valves. -If leakage is found from intake or exhaust valves, remove cylinder head and inspect valve seats. -The complete cylinder head must be replaced if valve seat damage is found. The valve seats can not be reworked. -Engine oil and filter should be changed after the repair. Workshop notes cylinder head repair: 1. The intake rocker arm roller is narrower than the exhaust and they must not be interchanged. Mark the rocker arms so they are reinstalled in their original location. 2. Inspect all parts that are being reused (i.e. camshafts, rocker arms) for signs of wear or damage. See WIS doc AH05.20-P-1000-09SZ for examples of normal and abnormal wear. Replace parts with new if damage or wear is found. 3. Check that all rocker arms are correctly located on the camshaft before installing cylinder head cover. Rotate engine at least 2 times and check that there are no problems with rocker arms. 4. The timing chain tensioner can be reused if it extends fully, has no noticeable problems in prior operation, and no chain drive components were replaced. 5. Care must be taken when removing fuel injectors to prevent damage. See WIS doc AR07.03-P-0004-03MM. 6. Cleanliness must be observed during repair to prevent subsequent complaint or engine damage:• When cleaning engine block surface, ensure oil ports are sealed to prevent debris from entering oil circuit. Refer to SI01.40-P-0010A. • No abrasive materials, sharp-edged tools, or unapproved cleaners should be used on engine block surface. Refer to AR01.00-P-0050-01A. • Any debris from cleaning that has entered the cooling jacket should be removed before assembly of engine. The debris can otherwise cause blockage in the cooling circuit leading to engine overheating. If any of the parts listed below are found damaged or in need of replacement during cylinder head valve‑seat diagnosis or repair, and the vehicle has warranty coverage, they must be claimed on a separate parts‑only line. These items are not covered under the cylinder head warranty extension and cannot be included with the claim. • Camshafts • Camshaft adjustment solenoids • Camshaft positioners • Fuel injectors • Hydraulic valve play compensating elements • Roller rocker arms • Spark plugs • Timing chain • Timing chain guide rails • Timing chain tensioner","document":{"url":"https://static.nhtsa.gov/odi/tsbs/2026/MC-11028267-0001.pdf","alternate_url":"https://static.nhtsa.gov/odi/tsbs/2026/MC-11028267-9999.pdf","confirmed":false},"url":"https://open.wenmarpro.com/bulletins/11028267","components":[{"id":"engine","name":"Engine","parent":null}],"codes":[],"topics":[],"vehicles":[{"make":"MERCEDES-BENZ","model":"A 220","year_from":2019,"year_to":2022,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"A 220 4MATIC","year_from":2020,"year_to":2021,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG A35","year_from":2020,"year_to":2021,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG A35 4MATIC","year_from":2020,"year_to":2020,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG CLA35","year_from":2020,"year_to":2024,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG CLA35 4MATIC","year_from":2020,"year_to":2020,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG CLA35 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLA 35","year_from":2024,"year_to":2025,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLA 35 4MATIC","year_from":2024,"year_to":2024,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLA 35 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLA35","year_from":2021,"year_to":2023,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLB35","year_from":2021,"year_to":2025,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"AMG GLB35 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"C 300","year_from":2018,"year_to":2023,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"C 300 4MATIC","year_from":2021,"year_to":2023,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"CLA 250","year_from":2019,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"CLA 250 4MATIC","year_from":2020,"year_to":2021,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"CLA 250 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"CLA 250+ (EV)","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"E 350","year_from":2020,"year_to":2023,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLA 250","year_from":2021,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLA 250 4MATIC","year_from":2021,"year_to":2021,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLA 250 4MATIC","year_from":2024,"year_to":2024,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLA 250 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLB 250","year_from":2020,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLB 250 4MATIC","year_from":2020,"year_to":2021,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLB 250 4MATIC","year_from":2026,"year_to":2026,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLC 300","year_from":2019,"year_to":2022,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLC 300 4MATIC","year_from":2023,"year_to":2023,"match":null,"vehicle_ids":[]},{"make":"MERCEDES-BENZ","model":"GLE 350","year_from":2019,"year_to":2023,"match":null,"vehicle_ids":[]}],"as_of":"2026-10-19","note":"A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.","attribution":[]}