Semi and Trailer Repair

Semi-trucks, also known as big rigs or 18-wheelers, are critical for transporting goods across the United States. However, like any complex machine, semi-trucks can experience electrical issues that cause breakdowns and delays. Some of the most common electrical problems in semi-trucks include:

Battery Issues

The battery is at the heart of a semi-truck’s electrical system, providing power to start the engine and run accessories like lights, HVAC, and onboard electronics. However, heavy use can wear out batteries quickly. Industry experts estimate batteries account for up to 25% of all big rig breakdowns.

Some common battery issues in semi-trucks include:

  • Dead Batteries – Extreme weather, long rest periods, and failing alternators can drain batteries. Attempting to jump-start a semi is difficult without a diesel push-start unit.
  • Corroded Terminals – Corrosion buildup increases resistance and prevents proper electrical contact. Periodic cleaning and preventative maintenance are required.
  • Old Batteries – Most semi-batteries last 3-5 years. Continuing to use old, worn-out batteries will lead to more breakdowns.

According to 2022 statistics from the American Trucking Association, the average age of a semi-truck on the road today is 9.6 years old. Older trucks are more susceptible to battery issues if preventative maintenance is lacking.

Alternator Failure

The alternator charges the batteries and powers truck electrics while the engine is running. The alternator is belt-driven off the engine and spins between 1,000 – 2,000 RPMs at cruising speed. This high-speed rotation generates a great deal of heat and vibration, placing strain on the alternator components.

Signs of a failing alternator include:

  • The battery not charging properly
  • Headlights or electronics dimming or flickering
  • Battery warning light illumination

Alternator bearings, brushes, diodes, and wiring are common failure points. On the 2022 top 10 breakdown list for heavy trucks, alternator issues rank #2 at 11.5% of service calls.

Starter Motor Failure

Like most vehicle engines, semi-trucks use a starter motor powered by the battery to turn over the engine for ignition. These heavy-duty starter motors have to spin diesel engines with 15 or more liters of displacement and generate 500 ft-lbs of torque or more.

Common causes of semi-starter motor failure include:

  • Overheating – Extended cranking to start the engine overheats the starter motor.
  • Electrical issues – Corroded wires and loose connections can affect starter operation.
  • Worn gears – The drive and flywheel starter gears eventually wear out from use.
  • Sticking solenoid – Corrosion and contamination can prevent the starter solenoid from closing properly.

Starter issues account for close to 10% of roadside service calls on heavy trucks based on statistics.

Electrical Shorts and Fires

Electrical shorts and arcing can happen in any vehicle but are more common in semi-trucks due to abundant wiring and electronics. Causes include:

  • Damaged wiring insulation – Vibration rubs and chafes wires, exposing conductors.
  • Corrosion – Moisture causes corrosion and resistance in connectors and terminals.
  • Loose connections – Vibration shakes electrical connectors loose over time.
  • Rodents – Mice, and rats chew through wire insulation.
  • Overloads – Too many accessories on one circuit can overload the wiring.

Electrical shorts can lead to fires in the dashboard, cab, engine compartment, trailer, or load. Fires are extremely dangerous for the driver and can cause extensive damage.

Lighting Issues

Semi-trucks rely heavily on lighting to operate safely at night. Lighting systems are complex with headlights, turn signals, brake and tail lights, marker lights, and Federal regulations to follow. Common lighting issues include:

  • Burned-out bulbs – Vibration shakes and breaks filaments over time.
  • Faulty sockets and wiring – Corrosion and vibration degrades connections.
  • Damaged lenses and reflectors – Lenses cloud and crack; reflectors tarnish and wear out.
  • Daytime running light failures – DRLs burn out quickly compared to normal headlights.
  • Misadjusted headlights – Headlights fall out of alignment over time and require adjustment.

According to a study by the AAA Foundation, 50% of semi-truck headlight systems fail to meet proper alignment and lighting. Furthermore, a survey of owner-operators indicated that 60% do not routinely check light operation. Poor lighting contributes to truck accidents, especially at night.

Trailer Electrical Problems

Semi-trucks haul a wide variety of trailers, from simple dry vans to complex reefer and car hauler trailers. Trailers also contain wiring and electrical components that can experience issues:

  • Corroded connectors – 7-way round connectors between the truck and trailer corrode over time from moisture and road contaminants.
  • Damaged lights and reflectors – As with tractor lighting, vibration can damage trailer lighting. Poor electrical grounds can also cause lighting failures.
  • Brake and turn signal faults – These critical circuits sometimes develop short or open connections.
  • ABS sensor failures – The ABS wheel speed sensors on the trailer can fail from road debris damage or corrosion.

It is critical to check trailer lighting before each trip as required by DOT inspection standards. Trailer ABS warning lights also should be scanned for fault codes.

Climate System Failures

Semi-truck cabs include climate control systems to keep drivers comfortable in extreme temperatures. The climate system contains an AC compressor, blower motor, actuators, sensors, switches, and wiring. Common problems include:

  • AC compressor failure – The AC compressor has a clutch that engages the drive pulley. Clutch failure is common.
  • Blower motor issues – Blower fan bearings wear out or moisture damages motor windings.
  • Stuck actuators – Climate control actuators control mode, temperature, and vent direction. These sometimes stick or fail.
  • Control head failures – The switch panel and control electronics stop working properly.

Up to 25% of roadside service calls relate to AC system failures based on commercial towing industry estimates. Lack of cab climate control impacts driver safety and retention.

Electronic System Malfunctions

Modern semi-trucks include electronic control modules (ECMs) that govern the engine, transmission, ABS, stability control, and other systems. Issues include:

  • Sensor failures – Crucial sensors for pressure, temperature, speed, and position output faulty data or stop working.
  • Wiring problems – Critical electronic wiring and connectors fall prey to vibration, corrosion, and rubbing.
  • Power spikes – Voltage spikes from jump starts, alternators, and accessories can damage delicate electronics.
  • Software glitches – ECM programming bugs, flashes, parameter changes, and incompatibility with new parts can cause drivability issues.
  • ECM failure – Extreme underhood heat and vibration stresses electronic control modules over time.

Truck downtime jumps exponentially when complex electronic systems malfunction. Most issues require a trip to the dealer for diagnosis and repair.

Trends and Industry Research

Industry groups like the American Trucking Association (ATA) and Commercial Vehicle Safety Alliance (CVSA) conduct ongoing studies into big rig breakdowns and their consequences. Some key statistics and trends include:

  • 20% of big rigs experience a breakdown each year, translating to 3-4 roadside service calls annually per truck.
  • 25% of all semi-truck breakdowns are battery-related. Alternator issues account for around 20%.
  • Upwards of 50% of semi-trucks fail vehicle inspection requirements for lighting systems.
  • AC-related issues are the #1 summertime breakdown problem.
  • Rodent damage to wiring is found in 1 in 5 trucks inspected during roadside checks.
  • Electronically controlled diesel engines have about a 25% higher breakdown rate compared to older mechanical engines.
  • The average heavy truck spends 3 days in the repair shop annually and is out of service 7 days per year.
  • Breakdowns cost fleets $168 per hour in lost driver wages, cargo delays, and towing fees.
mobile truck repair

Major Semi-Truck Brands in the US

The United States semi-truck market is dominated by three major brands;

Freightliner – Freightliner is the most popular semi-truck brand in America, holding over 35% market share. Models include the Cascadia, Columbia, Century Class, and regional haul trucks. Owned by Daimler Trucks North America.

Kenworth – Kenworth has a long-standing reputation for premium quality and operates several manufacturing plants in the US. Flagship models are the T680 and W900. Owned by Paccar.

Peterbilt – Peterbilt is another leading brand known for comfort, styling, and reliability. Key models are the 579, 389, 367, and regional haul 365. Also owned by Paccar.

Other significant US brands include:

  • International – International truck brands include the LT Series, RH Series, HV Series, and MV Series. Owned by Navistar.
  • Mack – Mack Trucks manufactures class 7 and 8 models like the Anthem, Pinnacle, Granite, and LR Series. Owned by Volvo Group.
  • Volvo – Volvo Trucks North America produces the VNL, VNR, VNX, VHD, and VAH models. Part of the Volvo Group.
  • Western Star – Western Star makes premium long-nose and heavy haul trucks. Owned by Daimler Trucks NA.
  • Hino – Hino Motors is a Japanese truck brand that produces medium-duty conventionals, COEs, and cabovers.
  • Mitsubishi Fuso – Fuso manufactures Class 3-5 cabover trucks in the US. Owned by Daimler Trucks.

Trends in the Phoenix, AZ Area

Phoenix, Arizona, and the surrounding region constitute one of the largest semi-truck hubs in the United States.

Key trends include:

  • Second highest level of semi-truck traffic after Los Angeles based on mileage.
  • Over 85,000 commercial trucking jobs in metro Phoenix according to the ATA.
  • Major freight corridors include I-10, I-17, and I-40 surrounding Phoenix. Also major warehouses in Glendale and distribution hubs in Mesa.
  • Phoenix is the closest major city to the California ports for inland transport of ocean freight. LA/Long Beach to Phoenix is 350 miles away.
  • Agriculture is big business with trucks hauling produce from Phoenix and Yuma farms to destinations east.
  • Construction trucks are numerous hauling materials and equipment to Phoenix’s many growing suburbs.
  • Foodservice distribution keeps trucks busy serving Phoenix’s large population and restaurant industry.
  • Fleets like Swift Transportation and Knight Transportation are among the city’s largest employers.
  • Hot, dusty conditions take a toll on truck cooling systems, filters, lighting lenses, and exterior finishes.

With its central location and diversified economy, the Phoenix area will continue to be a major hub for the semi-truck industry in the years ahead. Proper truck maintenance and driver training in this demanding desert environment will remain a high priority.


What are the most common roadside repairs for semi-trucks?

The most common roadside repairs for semi-trucks are related to electrical system issues, tires, brakes, and cooling systems. Battery problems, lighting failures, starter issues, and alternator breakdowns make up a large portion of electrical repairs.

How can truckers prevent electrical problems?

Routine maintenance and inspection of the electrical system is key. Clean battery terminals, check grounds, inspect wiring conditions, monitor alternator output, and perform light checks regularly. Have annual inspections to catch issues early.

What should truckers do if they experience an electrical failure on the road?

If safe, pull over immediately when an electrical issue occurs. Turn on hazard lights, set out triangles, and notify dispatch. Do not reset or try to repair major issues yourself. Call for roadside assistance or a tow truck to have it properly diagnosed and fixed.

Where are electrical components located on semi-trucks?

Electrical components are located throughout the tractor and trailer. The batteries and a control box/fuses are typically found in external battery boxes. Alternator and starter on the engine. Lights on the exterior. Sensors, ECUs, and wiring harnesses throughout the chassis. Trailer lighting and ABS at the rear.

How much downtime or costs happen due to electrical failures?

Studies indicate the average semi-truck spends 3 days in the shop each year for repairs, with electrical issues accounting for a significant portion. Breakdowns cost fleets an estimated $168 per hour plus towing fees. Prompt repairs are crucial.

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