Symptom hub
Troubleshoot Heavy Equipment Problems by Symptom
Start from the symptom when the root cause is still unclear. These clusters help technicians move from a complaint such as no start, black smoke, coolant loss, or repeated regen requests into a more disciplined diagnostic path.
No start / no fuel
Use these guides when the machine cranks but will not start, starts then dies, loses fuel prime, will not bleed, or fuel does not appear to reach the injectors.
Hitachi 6HK1 Cranks But Won't Start
Separate low-pressure supply, air intrusion, priming, rail pressure, control-side behavior, pump-side, and injector concerns.
Hitachi ZX350 Low Fuel Pressure
Start with supply restriction, air intrusion, filters, seals, and water separator before pump, injector, or sensor conclusions.
Komatsu SAA4D95LE Starts Then Dies
Separate unstable fuel supply, air intrusion, incomplete priming, shutoff behavior, control logic, and pump-side suspicion.
Komatsu SAA6D107E No Start No Fuel
Separate air lock, priming failure, supply restriction, shutoff/control behavior, rail pressure, pump-side, and injector-side suspicion.
Cat 3306 No Fuel to Injectors
Separate air lock, priming issues, supply restriction, and transfer or pump-side suspicion.
Cat 3306 Hard Start After Sitting
Diagnose fuel drain-back, air intrusion, restricted supply, and injection-side concerns.
Volvo D7 No Fuel No Start
Work through air lock, priming failure, supply restriction, shutoff, and pump-side branches.
Volvo D4 Starts Then Dies
Separate fuel loss, air intrusion, priming failure, shutdown command, and actuator behavior.
Komatsu SAA6D125E Low Fuel Pressure
Separate supply restriction, fuel aeration, filter and seal issues, pressure control, pump-side, and injector-side concerns.
Excavator Won't Start
A broader no-start page for crank, no-crank, fuel, battery, and start-enable complaints.
Low power
Low-power complaints need separation between true engine rpm loss, fuel supply, air/boost, derate, hydraulic load, and machine-mode concerns.
Hitachi ZX210 Low Power Under Load
Separate engine rpm loss, hydraulic load, fuel supply, air/boost limitations, derate, and deeper engine concerns.
Hitachi ZX120 Engine Bogs Down When Hot
Compare fuel restriction, engine power, hydraulic pump load, pump control behavior, overheating, and hot-condition leakage.
Komatsu SAA4D107E Low Power Under Load
Separate engine rpm loss, hydraulic load, fuel supply, air/boost limits, work mode, derate, and deeper engine concerns.
Volvo D5E Low Power
Separate engine power, fuel supply, air/boost, hydraulic load, and control-side limitations.
Volvo D8 Power Loss with Black Smoke
Compare intake restriction, boost leakage, turbo response, fuel delivery, and injector suspicion.
Komatsu SAA6D107E Low Power with Black Smoke
Separate intake restriction, boost leaks, charge-air problems, fuel delivery, injector suspicion, and control behavior.
Komatsu SAA6D125E Low Fuel Pressure
Use when low power or derate appears fuel-pressure related and the branch may be supply, aeration, control, pump, or injectors.
Black smoke
Black smoke normally points toward an air/fuel imbalance or combustion quality issue. Start by separating air supply, boost leakage, turbo response, fuel delivery, injectors, and control behavior.
Volvo D8 Power Loss with Black Smoke
A practical branch-based guide for black smoke under load with weak machine response.
Komatsu SAA6D107E Low Power with Black Smoke
Diagnose black smoke under load by comparing air supply, boost leakage, fuel delivery, injectors, and control behavior.
Volvo D6J Knocking and Smoke
Separate black, white, or mixed smoke from injector, fuel, air, boost, and mechanical branches.
White smoke
White smoke should be separated by timing, smell, warm-up behavior, rough running, coolant loss, and whether the smoke is fuel-related or steam-like.
Hitachi ZX210 White Smoke on Startup
Separate cold-combustion smoke, unburned fuel, injector or cylinder concerns, fuel quality, and coolant-related smoke.
Komatsu SAA6D125E White Smoke
Separate cold-start smoke, unburned fuel, injector or cylinder concerns, fuel quality, and coolant-related smoke.
Volvo D16 Cold White Smoke
Separate cold combustion, unburned fuel, injector or cylinder concerns, and coolant-related smoke.
Volvo D6J Knocking and Smoke
Use smoke color and operating condition to separate injector, fuel, air, and mechanical causes.
Coolant loss / cooling pressure
Cooling complaints need careful separation between external leaks, trapped air, cap or reservoir behavior, circulation, airflow, pressure-related leaks, and combustion-pressure suspicion.
Hitachi ZX350 Overheating
Separate cooling-side faults, airflow restriction, radiator or cooler package problems, trapped air, circulation, and internal concerns.
Komatsu SAA6D114E Overheating
Separate coolant level, airflow, radiator restriction, circulation, trapped air, cooling pressure, and internal-engine concerns.
Volvo D16 Cooling System Pressure
Separate cooling-side faults, trapped air, circulation issues, and internal-engine concerns.
Volvo D13 Cooling System Pressurizing
Compare heat-load pressure, fast cold pressure rise, bubbling, and coolant displacement.
Volvo D13 Coolant Loss
Track external leaks, hot pressure leaks, doser coolant-line leaks, and internal suspicion.
Cat 3306 Pressure in Cooling System
Diagnose cooling pressure without jumping straight to head gasket or cracked-head conclusions.
Cat C15 Blowing Coolant but No Hydrocarbons
Understand negative or inconclusive hydrocarbon results, cooling faults, and compressor branches.
Regen / DPF / DEF problems
Aftertreatment complaints need separation between soot loading, failed regen conditions, DEF or SCR behavior, derate, dosing, sensor feedback, DPF restriction, and ash service.
Hitachi ZX210 Regen Problems
Separate soot loading, regen completion, DEF/SCR behavior, sensor feedback, duty cycle, and engine-side soot causes.
Volvo D8 Regen Problems
Separate soot loading, failed regen, DPF restriction, sensor/control issues, and ash concerns.
Komatsu SAA6D107E Regen Problems
Separate soot loading, failed regen conditions, engine-side soot causes, DPF/KDPF restriction, and ash concerns.
Komatsu SAA6D125E Regen Problems
Separate soot loading, incomplete regen, KDPF restriction, DEF/SCR concerns, engine-side soot, and ash limits.
Cat C9.3 Regen Problems
Compare soot loading, regen initiation, completion problems, and aftertreatment conditions.
Cat C9.3 DPF Ash Service
Understand ash vs soot and when DPF cleaning, service, or replacement enters the discussion.
Cat C7.1 DEF Derate Won't Clear
Separate active root faults, latched inducement, dosing issues, DEF quality, and recovery logic.
Misfire / rough running
Misfire and rough running complaints need branch separation between injector behavior, wiring, cylinder contribution, compression, valve-train condition, fuel quality, and control-side suspicion.
Hydraulic issues
Hydraulic complaints should be separated by whether one function is weak, the whole machine is slow, pressure is low, oil condition is poor, or engine load is being mistaken for hydraulic weakness.
Hitachi Hydraulic Power Loss When Hot
Separate engine power, hydraulic oil temperature, pump control, relief behavior, pilot pressure, internal leakage, and wear.
Hitachi ZX120 Engine Bogs Down When Hot
Use when the engine bogs after warm-up and the branch may be fuel, engine power, hydraulic pump load, or control behavior.
Komatsu Hydraulic Power Loss When Hot
Separate engine rpm, hydraulic oil temperature, pump control, relief behavior, internal leakage, and component wear.
Hydraulic System Troubleshooting
A practical overview for pressure, flow, pump, valve, leakage, and contamination branches.
Hydraulic Pressure Low
Start with low hydraulic pressure, weak movement, slow response, and poor machine force.
Volvo D5E Low Power
Useful when hydraulic load may be mistaken for engine low power or machine bogging.
Komatsu SAA4D107E Low Power Under Load
Use when engine rpm loss, hydraulic demand, work mode, attachment load, fuel, or boost may be part of the same complaint.
Air system
Air-system complaints need separation between poor build, overpressure, constant purge, governor behavior, unloader behavior, dryer faults, and deeper compressor suspicion.
Why symptom troubleshooting still needs machine context
A symptom such as no start, low power, white smoke, or regen failure can point to different branches depending on the brand, engine family, system layout, service history, and duty cycle.
Why context matters
OEM brand-specific knowledge base
Understand how brand, machine, engine, system, and symptom context helps SERA support more practical troubleshooting paths.
Platform overview
What is SERA?
See how SERA supports heavy equipment mechanics and workshops with structured service and troubleshooting workflows.
AI for repair work
SERA vs generic AI chatbots
Compare generic AI answers with SERA's technician-led, brand-aware repair support approach.
Use SERA to keep the diagnostic path structured
SERA helps technicians convert broad symptoms into branch-based checks, document what changed, and avoid losing time to repeated part swapping or unclear repair logic.