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Key Responsibilities and Required Skills for Diesel Mechanic

💰 $45,000 - $95,000

MaintenanceTransportationSkilled TradesAutomotiveFleet

🎯 Role Definition

The Diesel Mechanic is responsible for the full lifecycle of diesel-powered vehicles and equipment maintenance: performing preventive maintenance, troubleshooting and diagnosing complex mechanical and electronic failures, executing repairs and overhauls, maintaining accurate maintenance records, and supporting fleet reliability and safety programs. This role requires strong diagnostic skills, familiarity with modern engine control modules (ECMs), hydraulic and powertrain systems, and the ability to communicate repair needs and timelines clearly to supervisors, drivers and customers. The ideal candidate increases equipment availability, reduces downtime through root-cause repairs and preventive actions, and supports continuous improvement within the shop or mobile service environment.

📈 Career Progression

Typical Career Path

Entry Point From:

  • Automotive Technician / Light-Duty Diesel Technician
  • Trade School Graduate — Diesel Technology or Heavy Equipment
  • Military Vehicle Mechanic (Army, Navy, Marines maintenance roles)

Advancement To:

  • Lead Diesel Mechanic / Senior Technician
  • Shop Supervisor / Foreman
  • Fleet Maintenance Manager / Maintenance Superintendent
  • Service Manager or Field Service Engineer

Lateral Moves:

  • Heavy Equipment Technician (construction, mining)
  • Mobile Service Technician (on-site fleet support)
  • Warranty/Technical Support Representative

Core Responsibilities

Primary Functions

  • Perform comprehensive diagnostics on diesel engines using onboard diagnostics, manufacturer software and handheld scanners to identify root causes for engine performance, fuel delivery, and emission control issues.
  • Conduct scheduled preventive maintenance (PM) including oil and filter changes, fuel filter replacement, coolant system service, belt and hose inspections, lubrication, and safety checks in accordance with fleet maintenance schedules and OEM recommendations.
  • Disassemble, inspect, repair and reassemble diesel engines, performing tasks such as cylinder head work, piston and ring replacement, crankshaft and bearing repairs, and complete engine rebuilds when required.
  • Diagnose and repair electronic control modules (ECMs), sensors, actuators and wiring harness issues; update ECM software and perform module calibrations per manufacturer procedures.
  • Troubleshoot and repair heavy-duty transmissions, clutches, torque converters, differentials and driveline components, including rebuilding gear sets, replacing seals, and correcting shifting or slippage issues.
  • Inspect, diagnose and repair hydraulic systems and components (pumps, valves, cylinders, hoses), including troubleshooting hydraulic leaks, pressure faults and component failures on heavy equipment and trucks.
  • Repair and replace fuel systems components (injectors, high-pressure fuel pumps, fuel lines, filters), perform fuel system diagnostics and correct fuel delivery problems affecting performance or emissions.
  • Service and repair air brake systems, ABS components, air compressors, valve/relay systems and related diagnostics to ensure regulatory compliance and safe operation.
  • Perform welding, fabrication and metal repair to patch frames, mounts, brackets and body components using MIG/TIG and oxy-acetylene techniques as required for structural repairs.
  • Conduct road tests and operational checks to validate repairs, confirm drivability, and identify any residual defects before releasing equipment back into service.
  • Replace and service cooling systems components including radiators, water pumps, thermostats, hoses and thermostatic controls; diagnose overheating and coolant loss issues using pressure tests and thermal diagnostics.
  • Install and maintain emission control systems such as SCR, DPF, DOC and associated dosing systems; perform DPF regeneration, cleaning and particulate monitoring to meet EPA and state regulations.
  • Maintain parts inventory controls: identify required parts, prepare accurate parts orders, verify deliveries and return defective items under warranty when applicable.
  • Complete accurate maintenance, repair and inspection documentation in the shop management system or CMMS, ensuring traceability of work performed, parts used, time charged and service recommendations.
  • Provide on-site mobile repairs and emergency roadside assistance for disabled trucks and equipment, including safe recovery procedures, temporary field repairs and communication with dispatch.
  • Interpret technical manuals, wiring diagrams, schematics and service bulletins to perform repairs to OEM standards and implement factory recalls or updates.
  • Mentor and train junior mechanics and apprentices, demonstrating safe procedures, efficient diagnostic approaches and best practices for preventative care and major repairs.
  • Enforce and follow all workplace safety protocols and PPE requirements, perform pre-use inspections of shop equipment and participate in safety meetings and certifications.
  • Collaborate with shop management and parts departments to estimate repair costs, prepare work orders, and communicate repair timelines and recommendations to drivers, fleet managers and customers.
  • Troubleshoot electrical systems including starters, alternators, batteries, charging systems and lighting circuits using multimeters, clamp meters and circuit testers to resolve intermittent or hard-fault electrical issues.
  • Perform axle and suspension repairs, including air suspension systems, leaf springs, bushings, shock absorbers, and alignments to restore ride quality and safe handling for heavy loads.
  • Overhaul and service PTOs, auxiliary power units and refrigeration units on refrigerated trailers (if applicable), ensuring auxiliary systems operate reliably and meet regulatory standards.
  • Conduct preventive inspections and safety inspections (pre-trip/post-trip) to verify vehicle roadworthiness and report non-conformances in accordance with company policy and DOT requirements.
  • Execute warranty claim processing and documentation, liaising with manufacturers and vendors to secure credit for covered parts and reduce out-of-pocket costs for the fleet.
  • Optimize maintenance procedures and recommend improvements to reduce cycle time, cost per repair and increase fleet uptime through root cause analysis and continuous improvement initiatives.

Secondary Functions

  • Assist with shop housekeeping, tool organization, and maintenance of diagnostic equipment to ensure an efficient and safe work environment.
  • Support parts sourcing and vendor relationships by researching substitute parts, identifying long-lead items and recommending stocking levels to minimize downtime.
  • Participate in cross-functional meetings with operations, safety and fleet management to align maintenance priorities with business objectives and service level agreements (SLAs).
  • Help prepare technical reports and failure analyses for fleet managers and stakeholders to inform capital replacement or overhaul decisions.
  • Provide input for technician schedules, overtime planning and mobile service routes to optimize coverage and emergency response capability.
  • Contribute to continuous training programs by attending manufacturer clinics, safety trainings, and internal knowledge-sharing sessions to stay current with emerging diesel technologies.
  • Support customer interactions: explain services performed, recommended repairs, estimated timelines and provide transparent updates on complex repair jobs.
  • Assist quality control and post-repair inspections to ensure work meets OEM standards and customer expectations before sign-off.
  • Participate in shop onboarding for new hires, ensuring compliance with certification requirements, safety rules and company policies.
  • Help maintain compliance documentation and inspection records to meet DOT, EPA and company audit requirements.

Required Skills & Competencies

Hard Skills (Technical)

  • Diesel engine diagnostics and repair (heavy-duty diesel engines, turbochargers, fuel injection systems)
  • Electronic Control Module (ECM) troubleshooting, reprogramming and calibration using OEM software and diagnostic tools
  • Heavy-duty transmission and driveline diagnostics and rebuilds
  • Hydraulic system troubleshooting and repair (pumps, valves, cylinders, hoses)
  • Air brake systems and ABS diagnostics, testing and component replacement
  • Diesel particulate filter (DPF), selective catalytic reduction (SCR) and emission system maintenance
  • Welding and fabrication (MIG/TIG, oxy-acetylene) for structural and body repairs
  • Use of diagnostic scanners, multimeters, oscilloscopes and pressure/flow testing equipment
  • Preventive maintenance procedures and fleet PM program execution
  • CMMS / Shop Management Software proficiency (e.g., TMT, RTA, Fleetio, MaintainX)
  • Parts identification, ordering and warranty claim processing
  • Road testing, load testing and operational validation after repair
  • Mechanical troubleshooting using schematics, blueprints and OEM service manuals
  • Tire, axle and suspension system maintenance and alignment basics
  • Refrigeration unit (thermo king, carrier) and auxiliary power unit (APU) service — if applicable

Soft Skills

  • Strong verbal and written communication with drivers, supervisors and vendors
  • Customer service orientation; ability to explain technical issues in plain language
  • Problem-solving and critical thinking for complex diagnostic scenarios
  • Attention to detail and high standard for workmanship
  • Time management and ability to prioritize repairs under tight schedules
  • Teamwork and mentoring aptitude for developing junior technicians
  • Adaptability to changing technology, tools and diagnostic procedures
  • Safety mindset and commitment to regulatory compliance (DOT, EPA)
  • Reliability, punctuality and professional work ethic
  • Documentation discipline for accurate service records and compliance reports

Education & Experience

Educational Background

Minimum Education:

  • High school diploma or GED; vocational training or technical certificates in diesel technology preferred.

Preferred Education:

  • Associate degree or diploma in Diesel Technology, Heavy Duty Mechanics, or Automotive Technology from an accredited trade school.
  • Manufacturer-specific training (Cummins, Detroit, CAT, Volvo, PACCAR) and ASE Heavy Truck certifications.

Relevant Fields of Study:

  • Diesel Technology / Heavy Duty Mechanics
  • Automotive Technology
  • Heavy Equipment Technology
  • Mechanical Engineering Technology
  • Welding and Fabrication Technology

Experience Requirements

Typical Experience Range: 2 - 8 years of progressive experience servicing diesel engines, heavy trucks, construction equipment, or fleet vehicles.

Preferred: 5+ years of hands-on diesel mechanic experience with documented work on heavy-duty engines, ECM diagnostics, transmissions, hydraulics and fleet PM programs; ASE certifications and/or manufacturer-authorized training; CDL and mobile service experience a plus.

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