Tampering with bus heater
393.77(b)(5) is a Other Vehicle Defect violation under 49 CFR §393.77(b)(5). It falls in the Vehicle Maintenance BASIC with a severity weight of 3/10.
Last updated May 2026
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Notes
DSMS: YIf this violation was written incorrectly, here are the angles trucking-safety managers use to contest it. Playbook: Vehicle Maintenance (general).
Common ways to challenge this code
The driver's pre-trip DVIR documented compliant brake adjustment and operation. The cited defect arose en route or was misclassified at roadside.
Evidence that wins
The required lamp was inoperative only momentarily due to vibration, temperature, or similar transient cause — explicitly exempted under §393.9.
Evidence that wins
The tread depth measurement was taken at a worn point that is not representative, contrary to NHTSA/FMCSA measurement standards.
Evidence that wins
Carrier's periodic-inspection records show the cited defect could not reasonably have existed at the time of inspection.
Evidence that wins
Common pitfalls — avoid these
Same BASIC category — ranked by national citation volume
Coupling - Semi-Trailer, drawbar slider cylinder leaking.
Tires - Less than 1/32 inch tread depth at 3 locations/2 adjacent tread grooves.
Coupling - Upper saddlemount has movement of more than 1/4 inch.
Coupling - Driveaway, pintle hook repair welded.
Coupling - Full Trailer, drawbar slider cylinder leaking.
Coupling - Pivot pin and bracket more than 1/4 inch horizontal movement.
Steering - C-Dolly has missing or inoperable steering locks.
Air Disc Brake - Lining/pad thickness less than 1/16 inch.
Codes under the same FMCSA violation group
393.77(b)(5) is the FMCSA roadside-inspection violation code for "Tampering with bus heater", part of the Other Vehicle Defect group, cited under 49 CFR §393.77(b)(5).
393.77(b)(5) falls under the Vehicle Maintenance BASIC in the FMCSA Safety Measurement System (SMS).
393.77(b)(5) carries a severity weight of 3 out of 10. Higher weights indicate violations more closely tied to crash risk, and they count more toward a carrier's Vehicle Maintenance score.
No. 393.77(b)(5) is not an out-of-service violation, so on its own it does not trigger an out-of-service order at the roadside.
The point contribution of 393.77(b)(5) depends on its severity weight (3/10) multiplied by a time weight of 3, 2, or 1 based on how recent the inspection is. You can calculate the exact contribution with the CSA points calculator.
Yes. If you believe 393.77(b)(5) was recorded in error, you can file a Request for Data Review (RDR) through the FMCSA DataQs system with supporting evidence. A successful challenge can remove or correct the violation on your record.
Keep going
Statistics
Ranked by roadside-inspection citation count across FMCSA public data.
Inoperable Required Lamp
State vehicle registration or License Plate violation
Operating a CMV without proof of a periodic inspection
Brake Out of Adjustment - Roto, Clamp (Short & Long), DD-3, or Bolt
No/discharged/unsecured fire extinguisher
Inoperative turn signal
Operating a CMV without documentation of a periodic inspection.
Tire-flat and/or audible air leak
Wipers - Inoperative / missing / damaged wipers.
Violation of Local Laws - Explain:
State/Local Laws - State registration/tag violation.
Emergency Equipment - Stopped vehicle warning devices missing or impr…
State/Local Laws - Speeding 6-10 miles per hour over the speed limit.
Brake - Defective brake(s) are equal to or greater than 20% of the se…
No or defective lighting devices or reflective material as required
Inspection, repair and maintenance of parts and accessories
CMV manufactured after 10/19/94 has an automatic airbrake adjustment …
Tire-other tread depth less than 2/32 of inch measured in a major tre…
Tires - All others, leaking or inflation less than 50% of the maximum…
Carrier name and/or USDOT Number not displayed as required