Recall 21V850 affects 1,434 2020-2022 Thomas Built Buses Saf-T-Liner Hdx and Efx school buses for loose alternator cables. Repair is free at dealers.
Thomas Built Buses is recalling 1,434 2020-2022 Saf-T-Liner Hdx and Saf-T-Liner Efx school buses because the alternator power cable stud nut was not tightened properly, leaving the cable connection loose. Electrical arcing from that loose connection can increase the risk of a fire, and Thomas Built Buses dealers will complete the recall repair free of charge.
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What's wrong?
The alternator on 2020-2022 Thomas Built Buses Saf-T-Liner Hdx and Saf-T-Liner Efx school buses keeps the electrical system charged while the engine runs. A heavy power cable attaches to a stud on the alternator, and a locking nut holds that cable tight so current flows cleanly from the alternator into the bus electrical system.
On affected buses, that nut was not tightened properly during installation at Thomas Built Buses. The parts themselves are not described as defective. The problem is the loose connection at the alternator. When the cable is not held firmly against the stud, the charging connection is unreliable and the bus can show an alternator or battery charging fault.
The warning sign is the battery charge light on the dash instrument cluster. If that light comes on, it points to a charging problem and matches the warning described for this recall.
Who's affected?
Covers both Saf-T-Liner Hdx and Saf-T-Liner Efx buses across the 2020, 2021, and 2022 model years, all tied to the same electrical system component.
| 2020 Thomas Built Buses Saf-T-Liner Hdx | electrical system |
|---|---|
| 2021 Thomas Built Buses Saf-T-Liner Hdx | electrical system |
| 2022 Thomas Built Buses Saf-T-Liner Hdx | electrical system |
| 2020 Thomas Built Buses Saf-T-Liner Efx | electrical system |
| 2021 Thomas Built Buses Saf-T-Liner Efx | electrical system |
| 2022 Thomas Built Buses Saf-T-Liner Efx | electrical system |
| Units affected | 1,434 |
| 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?
A loose alternator power cable connection creates a fire risk if it arcs. Treat a battery charge light as a warning sign for the alternator or cable connection, and schedule the recall repair soon. Repair is free at any franchised Thomas Built Buses dealer.
What should I do?
- Check your VIN to confirm your 2020-2022 Thomas Built Buses Saf-T-Liner Hdx or Saf-T-Liner Efx is included in this recall.
- Contact a franchised Thomas Built Buses dealer to schedule the free alternator power cable inspection and tightening, which fixes the loose cable connection behind the fire risk.
- Bring the recall notice if Thomas Built Buses mailed one. If not, reference recall number 21V850 when you call.
- Avoid placing the bus back into route service until the dealer confirms the alternator power cable connection is secure.
- Call Thomas Built Buses customer service at 1-800-547-0712 with questions about recall number 21V850.
What happens at the repair
At the dealer, a Thomas Built Buses technician inspects the alternator power cable connection and tightens the connection when needed. The inspection and any tightening are free under recall 21V850. The owner letter explains the reimbursement process for related repairs paid before the recall notice. If you've already paid for an alternator power cable connection repair, use the instructions in that letter or contact DTNA customer service to ask how to submit your claim.
| Reimbursement | Reimbursement available |
|---|
Timeline
| November 2, 2021 | NHTSA published the recall |
|---|---|
| December 17, 2021 | Owner notification mailed |
| December 31, 2021 | Dealer notification began |
| December 31, 2021 | Dealer notification ended |
| December 31, 2021 | Interim owner notification (was planned for this date) |
Frequently asked questions
What is recall 21V850?
Recall 21V850 covers 1,434 2020-2022 Thomas Built Buses Saf-T-Liner Hdx and Saf-T-Liner Efx school buses with an alternator power cable stud nut that was not tightened properly. A loose connection can cause electrical arcing and increase fire risk. Dealers will inspect and tighten the connection for free.
What should I do if my 2020-2022 Thomas Built Buses Saf-T-Liner Hdx or Saf-T-Liner Efx is on this recall?
Check your VIN to confirm your specific bus is included in recall 21V850. If it is, contact a franchised Thomas Built Buses dealer to schedule the alternator power cable inspection and tightening. Reference recall 21V850 or DTNA recall FL904 when you call.
Is the recall repair free?
Yes. Federal recall law requires the manufacturer to repair the defect at no cost. Thomas Built Buses dealers will inspect the alternator power cable connection and tighten it if necessary, free of charge.
What is the safety risk?
The safety risk is fire from electrical arcing at a loose alternator power cable connection. If your VIN is included, arrange the free dealer inspection and tightening before keeping the bus in regular service.
When were owners notified about recall 21V850?
Owner notification letters were mailed on December 17, 2021. If you bought the bus used or never received a letter, check your VIN and contact a franchised Thomas Built Buses dealer with recall number 21V850 or DTNA recall FL904.
More information
| NHTSA campaign page | nhtsa.gov/vehicle-recalls/21V850000 |
|---|---|
| Thomas Built Buses customer service | 1-800-547-0712 |
| NHTSA recall # | 21V850 |
| NHTSA recall # (full) | 21V850000 |
Source documents
-
Download Recall Document (PDF) (PDF) - Download Quarterly Report (PDF)
- Download Owner Notice (PDF)
- Download Recall Report (PDF)
- Download Misc. Document (PDF)
- Download Owner Notification Letter (PDF)
- Download Recall Acknowledgement (PDF)
This article is generated from NHTSA's primary recall filings and reviewed against the source on May 20, 2026. RecallNotify does not paraphrase NHTSA's consequence language; that text is reproduced as written above. Editorial standards →