Mercedes-Benz bulletin LI49.20-N-079593
What it saysCheck engine light with fault code P20EEFE in the CDI control unit CDI (N3/47) Complaint Check engine light is illuminated with fault code P20EEFE "The efficiency of component 'SCR catalytic converter' is not… NHTSA’s full summary ↓
Mercedes-Benz filed this with NHTSA as a service bulletin dated Jul 25, 2025, received Aug 1, 2025. It names 3 model years (2019–2021). A service bulletin is not a safety recall: it is the manufacturer telling its dealers how to diagnose or repair a condition, and whether the work is paid for depends on the warranty in force. Quoting the number at a service desk can save a diagnosis.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationCheck engine light with fault code P20EEFE in the CDI control unit CDI (N3/47) Complaint Check engine light is illuminated with fault code P20EEFE "The efficiency of component 'SCR catalytic converter' is not sufficient" stored in the CDI control unit (N3/47). Cause Excessive ammonia slip is being detected in the SCR system, often triggered by IUMPR (In-Use Monitor Performance Ratio) thresholds. This typically indicates that the SCR catalyst is not converting DEF (AdBlue) efficiently under moni- tored conditions. Common Driving Scenario: •Non-dynamic driving (e.g., highway cruising with cruise control set) •Minimal load changes, steady-state exhaust flow Contributing Factors: •Software influence – IUMPR (In-Use Monitor Performance Ratio) thresholds •DEF Overdosing – Over-injection due to faulty NOx sensors, dosing valve issues, or poor DEF quality •Low Exhaust or Catalyst Temperatures – Common under low-load conditions; reduces SCR conversion efficiency •Catalyst Degradation or Contamination – Aging catalyst or contamination from oil, coolant, or poor-quality DEF Remedy IMPORTANT: Do not replace any components unless instructed through TIPS. For Model Year 2019–2021 Vehicles: •Update the following control units to the latest available software: N3/47 - Motor electronics 'CDI43' for combustion engine 'OM651' (CDI) N118/5 - Selective catalytic reduction (SCR GEN3) •If no newer software is available, proceed with the inspection and documentation steps listed under the No Newer Software section. •Once all inspections are complete, open a TIPS case directed to the Powertrain Inbox, referencing this LI with the collected information and data. No Newer Software Vehicles: Perform the following steps in order. Document all findings with photos and actual values where applicable: 1. Tailpipe Wipe Test •Perform and photograph results. 2. NOx Sensor Harness Inspection •Check connectors, pins, crimps, and harnesses 3. Sensor Plausibility Checks •Record actual values for all pressure and temperature sensors: •Once with the engine cold (≥8 hours off) •Again, at full operating temp, engine idling 4. Smoke Test – Intake, Charge Air, Exhaust •Apply ≤26 psi from the tailpipe. •Seal at clean air line. •Manipulate components during the test. •Document any leaks. 5. DPF Data •Record actual values and regeneration history. 6. SCR Temp Sensor Wiring •Inspect wiring and p
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| LI49.20-N-079593 | Service bulletin | Jul 25, 2025 | 11021173 | PDF, 40 KB |
The summary is NHTSA’s abstract of the document, as filed under 49 CFR 579.5. One communication is usually filed as several documents — the bulletin, a dealer notice, an owner letter — and the number on any of them finds this page. A PDF link is shown only once NHTSA’s own server has been seen to serve that document; the rest are checked over the following nights. Quote the number at a service desk; it is what the dealer’s system is keyed on.
Model years it names
Source: as the manufacturer filed themA vehicle page’s bulletin list shows the newest few communications filed against that model year; the count there is every one.
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What owners reported
Source: NHTSA complaint databaseOwners of the 3 model years this bulletin names have filed 281 complaints with NHTSA since 2015.
A complaint is one owner’s account, not a defect finding, and a bulletin is not a recall. Nothing here says this bulletin was issued because of these complaints, or that the repair it describes fixed them. Complaint files on this site begin in 2015.
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Mercedes-Benz, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is Mercedes-Benz LI49.20-N-079593 a recall?
No. A service bulletin is a manufacturer communication filed with NHTSA under 49 CFR 579.5; a safety recall carries an NHTSA campaign number (two digits, a letter, six digits) and a federal duty to repair for free. Check the vehicle’s recalls by VIN at nhtsa.gov/recalls, or on its page here.
Is the LI49.20-N-079593 repair free?
Not automatically. A service bulletin describes how to diagnose or repair a condition; who pays depends on the warranty in force, any extension, and the dealer. Quoting the number can save a diagnosis either way. Every Mercedes-Benz warranty extension on file lists the ones Mercedes-Benz has filed.
Which vehicles does LI49.20-N-079593 cover?
The manufacturer filed it against 3 model years: 2021 Mercedes-Benz Sprinter, 2020 Mercedes-Benz Sprinter, 2019 Mercedes-Benz Sprinter. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.