Glossary
Diesel Mechanic Terms & Vocabulary
15 essential diesel mechanic terms with plain-English definitions: the vocabulary you’ll hear in training and on day one.
Key diesel mechanic vocabulary
These 15 terms come up constantly in diesel mechanic training, on the job and in interviews. Knowing them helps you follow instructions, document accurately and sound prepared.
- Air dryer
- Removes moisture from compressed air in brake systems.
- Compression ignition
- Diesel combustion where fuel ignites from the heat of compressed air.
- DEF
- Diesel exhaust fluid: a urea solution used by SCR systems.
- DPF
- Diesel particulate filter: traps soot from exhaust.
- ECM
- Engine control module: the engine’s computer.
- EGR
- Exhaust gas recirculation: returns some exhaust to the intake to lower emissions.
- J1939
- The communication protocol used on heavy-duty vehicle networks.
- Out-of-service criteria
- Defects that make a vehicle unsafe to operate until repaired.
- PM
- Preventive maintenance: scheduled service to prevent breakdowns.
- Pushrod stroke
- How far the brake chamber pushrod travels: used to check brake adjustment.
- Regeneration (regen)
- Burning off soot collected in the DPF.
- SCR
- Selective catalytic reduction: reduces nitrogen oxide emissions.
- Slack adjuster
- A lever connecting the brake chamber pushrod to the brake camshaft.
- SPN / FMI
- Suspect parameter number and failure mode identifier: parts of heavy-duty fault codes.
- Turbocharger
- Uses exhaust energy to compress intake air.
Practice these terms
Test yourself with the free Diesel Mechanic practice test: it includes vocabulary questions built from this list. For a complete course, see Diesel Mechanic training.
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