Common Fleet Maintenance Errors That Cause Unnecessary Downtime

When your fleet sits idle, you’re losing money like oil leaking from a cracked pan. The root cause of that unplanned downtime? More often than not, it’s due to preventable maintenance errors that pile up until something breaks.

We see the same costly mistakes come through our bays week after week. Some are due to rushed service. Others come from skipping routine inspections. But all of them could’ve been caught early—and fixed faster—if the fleet was running a tighter maintenance game. Here are the top errors that lead to unnecessary downtime, and what you can do to keep your trucks on the move.

Ignoring Scheduled Preventive Maintenance Intervals

It’s easy to push maintenance when your trucks are busy, but that short-term thinking always backfires. Skipping intervals leads to missed warning signs and major component failures. By honoring your PM schedule, you prevent small issues from becoming shutdowns.

• Engine oil negligence: Leads to increased friction and premature wear across internal components.
• Transmission service delays: Cause fluid breakdown and gear slipping, especially under load.
• Brake inspections skipped: Allow worn shoes or slack adjusters to become DOT violations—or worse, failures.
• Air filter replacements: When ignored, restrict airflow and reduce fuel economy across the entire fleet.
• Coolant system neglect: Can result in overheating and warped engine heads during heavy hauling or summer heat.

Relying on Visual Inspections Alone

A walkaround can catch obvious problems, but too many fleets stop there. Without deeper inspections and diagnostics, hidden failures go unnoticed until it’s too late.

• Undiagnosed battery issues: Appear fine until extreme weather exposes a weak charge or bad cell.
• Driveline vibration: Often dismissed until it becomes a full U-joint failure that takes a truck off the road.
• Undetected ABS faults: Can silently deactivate trailer brakes, only showing symptoms during emergency stops.
• Cracked belts and hoses: Easy to miss unless physically tested or measured for wear.
• Wheel bearing wear: Can feel smooth during rotation but lead to catastrophic failures under highway load.

Failing to Track Maintenance Histories Across the Fleet

If you’re not logging every service and repair per unit, you’re flying blind. Maintenance histories offer essential insights into performance patterns, part lifespans, and recurring issues. Without a reliable record, you risk over-servicing some vehicles and completely neglecting others. A fleet with no history log can reduce uptime, and result in more often than not. Having a good track record will increase the value of your vehicle. 

Overlooking Trailer Maintenance

Truck tractors often get the lion’s share of attention, but trailers are just as critical to uptime. Common failures like corroded wiring, broken air lines, or neglected wheel seals can sideline a trailer just as fast as an engine failure. Don’t forget—DOT inspectors don’t care if it’s the truck or trailer failing the check. Routine trailer PMs should include full brake, suspension, lighting, and tire inspections every time a unit comes off the road.

Downtime-Causing Mistakes to Watch Out For

• Forgetting BIT inspections on a 90-day schedule
• Delaying DPF and emissions system regens
• Running mismatched tires across duals
• Ignoring driver complaints about steering “pull”
• Skipping alignment after suspension repairs
• Relying on generic fluids instead of manufacturer specs
• Allowing coolant to run below freezing-point protection levels
• Failing to update software for ECM-controlled components

Letting Untrained Personnel Handle Diagnostics

Just because someone can clear a fault code doesn’t mean they should. ECM-controlled systems require platform-specific knowledge and tooling, like Cummins INSITE or Bendix brake diagnostics. If your team isn’t trained or the shop you’re using can’t pull detailed logs, you’re not diagnosing—you’re guessing. That leads to repeat visits, missed problems, and driver frustration that costs you long after the truck is “fixed.”

Stop Letting Small Errors Cause Delays

Fleet maintenance isn’t just about keeping trucks running—it’s about building uptime into your operations. From skipping scheduled intervals to misdiagnosing critical components, small errors add up fast and take down trucks when you need them most. By identifying these preventable mistakes, you keep your fleet rolling longer, your drivers safer, and your customers happier.

B&B Truck & Trailer Repair in Colona, IL, helps fleets avoid downtime with proactive inspections, certified technicians, and a data-driven approach to diesel maintenance. Don’t wait until the next truck is towed in—get ahead of downtime before it costs you more than a repair. For more information, read our article on why you should get fleet maintenance.