Recall 21V538 affects 78 2020-2021 Gillig Low Floor vehicles for excessive ammonia in exhaust. Repair will be free at any franchised Gillig dealer once available.
Gillig is recalling 78 2020-2021 Low Floor buses under recall 21V538 because Cummins L9 engine calibration software can send too much Diesel Exhaust Fluid through the exhaust system, allowing excessive ammonia into the tailpipe exhaust. Exposure to high ammonia levels can increase the risk of injury, and the Gillig dealer repair will be free once the final remedy is available.
Does this recall apply to your specific vehicle?
The official, free per-VIN recall check is run by NHTSA. Enter your VIN and we'll forward you directly — and add you to a free watchlist so you hear about new recalls for your vehicle.
Check my VIN at NHTSARecallNotify doesn't check your VIN — NHTSA's official tool does. We use your email only to alert you to new recalls.
Watch this vehicle for recalls
Add it to your free watchlist and we will alert you as new federal recalls are posted for your year, make and model. New-recall alerts are rolling out now.
You are on the watchlist.
We will email you as new federal recalls are posted for your vehicle.
What's wrong?
The Cummins L9 diesel engine in 2020-2021 Gillig Low Floor buses uses Diesel Exhaust Fluid, or DEF, to help clean exhaust after combustion. Engine calibration software controls when and how that fluid is injected into the exhaust stream. When the dosing is correct, the system reduces emissions before exhaust leaves the tailpipe.
On affected buses, the software manages DEF injection in a way that lets excessive ammonia reach the tailpipe exhaust. The issue is software calibration, not a broken exhaust pipe or muffler. Gillig says the updated calibration carries a unique part number, which helps confirm that the corrected software is installed.
The filing does not describe a dashboard light, noise, or drivability change before the condition occurs. The warning concern is exposure: ammonia at elevated concentrations can injure people near the tailpipe exhaust.
Who's affected?
Covers the 2020 and 2021 Low Floor buses with the same exhaust-system component listed for both years.
| 2021 Gillig Low Floor | Manifold/header/muffler/tail pipe |
|---|---|
| 2020 Gillig Low Floor | Manifold/header/muffler/tail pipe |
| Units affected | 78 |
| Field incidents | NHTSA has logged no field incidents to date. |
The year and model narrow the scope, but the VIN decides. Check your VIN to confirm whether your specific bus is included.
What's the safety risk?
High ammonia exposure increases the risk of injury. If ammonia exposure is suspected, move away from the bus, keep passengers clear, and arrange service before regular operation continues. Repair will be free at any franchised Gillig dealer once available.
What should I do?
- Check your VIN to confirm your 2020-2021 Gillig Low Floor is included in this recall.
- Wait for Gillig to confirm the free Cummins engine recalibration is open before scheduling the final repair.
- Contact Gillig customer service at 1-510-264-5073 for current remedy timing and reference recall number 21V538 when you call.
- Keep the bus out of service for exhaust-related passenger exposure concerns until Gillig gives repair or interim instructions.
What happens at the repair
Once the remedy is available, a Gillig technician will recalibrate the engine software that controls Diesel Exhaust Fluid injection. The final dealer repair will be free under the recall, with parts and labor covered. Out-of-pocket repairs already paid are handled through the manufacturer's limited warranty, not through a separate reimbursement program, because eligible product failures before the owner notice would have been replaced under warranty. If you have prior repair paperwork, ask the service desk how the limited warranty applies.
| Reimbursement | Warranty coverage applies |
|---|
Timeline
| July 15, 2021 | NHTSA published the recall |
|---|---|
| October 4, 2021 | VIN-searchable in NHTSA's database — Check your VIN to see whether this recall applies to your specific vehicle. |
| October 4, 2021 | Interim owner notification (was planned for this date) |
| October 14, 2021 | Owner notification mailed |
Frequently asked questions
What is recall 21V538?
Recall 21V538 covers 78 2020-2021 Gillig Low Floor vehicles with Cummins L9 diesel engines. The engine calibration software can allow excessive ammonia into the tailpipe exhaust, and exposure to high levels of ammonia can increase injury risk.
What should I do if my 2020-2021 Gillig Low Floor is on this recall?
Check your VIN to confirm your specific bus is included in recall 21V538. If it is, contact Gillig customer service at 1-510-264-5073 and ask when the Cummins engine recalibration is available for your vehicle. Reference recall number 21V538 when you call.
Is the recall repair free?
Yes. Gillig's remedy states that Cummins will recalibrate the engine free of charge. Federal recall law requires the manufacturer to provide the recall remedy at no cost, including the calibration work needed to address the diesel exhaust fluid injection issue.
What is the safety risk?
The safety risk is exposure to high levels of ammonia from the tailpipe exhaust. The recall filing says that exposure to high levels of ammonia can increase the risk of injury. Until the recalibration is complete, follow Gillig's guidance for operating and servicing the bus.
More information
| NHTSA campaign page | nhtsa.gov/vehicle-recalls/21V538000 |
|---|---|
| Gillig customer service | 1-510-264-5073 |
| NHTSA recall # | 21V538 |
| NHTSA recall # (full) | 21V538000 |
Source documents
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 →