Recall 21V120 affects 159 2019-2021 Thomas Built Buses Saf-T-Liner C2 school buses for engine-control software. Repair is free at any franchised Thomas Built Buses dealer.
Thomas Built Buses is recalling 159 2019-2021 Saf-T-Liner C2 school buses under recall 21V120 because the engine control module software is calibrated incorrectly. That error can keep safety functions for braking, traction and stability control, speed control, or collision avoidance from limiting engine speed or torque as intended, which increases crash risk; Thomas Built Buses dealers will update the software free of charge.
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What's wrong?
The engine control module on the 2019-2021 Thomas Built Buses Saf-T-Liner C2 is the engine computer for the Cummins B6.7N engine. It reads commands from the bus and sets engine speed and torque, including requests from braking, traction control, stability control, speed control, and collision avoidance systems.
On affected buses, the software calibration is wrong. When a safety-related system sends a request over the vehicle data network to reduce engine speed or limit torque, the engine does not respond as designed. That leaves those systems without the engine reduction they expect while they are trying to manage braking, wheel slip, vehicle stability, speed, or a collision avoidance function.
There is no warning sign before failure. A driver or fleet technician should not expect a dashboard light, noise, or drivability change to identify this software error before a safety-related function asks the engine to cut speed or torque.
Who's affected?
Across the 2019, 2020, and 2021 model years, the recall names both the engine and engine-control software for Saf-T-Liner C2 buses.
| 2019 Thomas Built Buses Saf-T-Liner C2 | Software |
|---|---|
| 2019 Thomas Built Buses Saf-T-Liner C2 | Engine |
| 2020 Thomas Built Buses Saf-T-Liner C2 | Software |
| 2020 Thomas Built Buses Saf-T-Liner C2 | Engine |
| 2021 Thomas Built Buses Saf-T-Liner C2 | Software |
| 2021 Thomas Built Buses Saf-T-Liner C2 | Engine |
| Units affected | 159 |
| Field incidents | NHTSA has logged no field incidents to date. |
A matching year and model does not guarantee inclusion. Check your VIN to confirm whether your specific bus is included.
What's the safety risk?
If braking, stability, speed, or collision avoidance functions do not work correctly, the bus has less help controlling speed and avoiding a crash. Drive cautiously, confirm whether the VIN is included, and schedule the recall repair soon if it applies. Repair is free at any franchised Thomas Built Buses dealer.
What should I do?
- Check your VIN to confirm your 2019-2021 Thomas Built Buses Saf-T-Liner C2 is included in this recall.
- Contact a franchised Thomas Built Buses dealer to schedule the free Cummins engine control module recalibration that restores engine speed and torque limits for braking, stability, speed control, and collision avoidance functions.
- Bring the owner letter if you have it. If not, reference recall number 21V120 and DTNA recall FL-879 when you call.
- Drive cautiously until the recalibration is complete. Leave extra following distance and report braking, stability, speed control, or collision avoidance concerns to the dealer.
What happens at the repair
At the dealer, the engine control module on the Cummins B6.7N engine is recalibrated so the software uses the correct limits for engine speed and torque during braking, traction control, stability control, speed control, and collision avoidance functions. The recall repair is free. Thomas Built Buses and Cummins handle the owner notice and service path, and the DTNA recall number is FL-879.
Timeline
| February 25, 2021 | NHTSA published the recall |
|---|---|
| March 29, 2021 | Owner notification mailed |
| April 25, 2021 | Dealer notification began |
| April 25, 2021 | Dealer notification ended |
| April 25, 2021 | Interim owner notification (was planned for this date) |
Frequently asked questions
What is recall 21V120?
Recall 21V120 covers 159 2019-2021 Thomas Built Buses Saf-T-Liner C2 school buses with Cummins B6.7N engines. The engine control module software calibration can prevent safety-related engine speed or torque limits from working as intended. Cummins dealers will recalibrate the software for free.
What should I do if my 2019-2021 Thomas Built Buses Saf-T-Liner C2 is on this recall?
Check your VIN to confirm your specific bus is included in recall 21V120. If it is, contact a Thomas Built Buses dealer or call 1-800-547-0712 for repair routing. Reference recall number 21V120 and FL-879 when you call. The software recalibration is free.
Is the recall repair free?
Yes. Federal recall law requires the manufacturer to repair the defect at no cost, and the remedy states that Cummins dealers will recalibrate the engine control module free of charge.
What is the safety risk?
The risk is that safety-related functions do not work properly. The affected engine software can interfere with intended limits tied to braking, traction and stability control, speed control, or collision avoidance, increasing crash risk. Confirm the VIN and arrange the free recalibration.
When were owners notified about recall 21V120?
Owner notifications were mailed on March 29, 2021. If you bought the bus used or never received the letter, the VIN still decides whether the recall applies. Check your VIN, then contact the dealer service desk with recall number 21V120.
More information
| NHTSA campaign page | nhtsa.gov/vehicle-recalls/21V120000 |
|---|---|
| Thomas Built Buses customer service | 1-800-547-0712 |
| NHTSA recall # | 21V120 |
| NHTSA recall # (full) | 21V120000 |
Source documents
-
Download Recall Document (PDF) (PDF) - Download Quarterly Report (PDF)
- Download Misc. Document (PDF)
- Download Owner Notification Letter (PDF)
- Download Owner Notice (PDF)
- Download Recall Report (PDF)
- Download Recall Acknowledgement (PDF)
This article is generated from NHTSA's primary recall filings and reviewed against the source on May 24, 2026. RecallNotify does not paraphrase NHTSA's consequence language; that text is reproduced as written above. Editorial standards →