Glossary of diagnostic acronyms

Code sheets and system pages use short industry acronyms. This glossary explains the ones that appear most often on TruckCodeLookup so you can read a sheet without leaving mid-sentence.

Jump to a term from a code page’s “Related terms” list, or scan the entries below.

Anti-lock Braking System — modulates brake pressure so wheels keep rotating under hard braking.

Aftertreatment Control Module — the computer that runs SCR/DEF dosing and NOx conversion monitors on many heavy diesels.

Automatic Traction Control (also called ASR) — limits drive-wheel spin using brake and/or engine torque intervention.

Camshaft Position sensor — tells the ECM where the camshaft is for injection and spark timing.

Parameter ID — a live data channel on a scan tool (wheel speed, NOx, O2 voltage, fuel trim, and so on).

Diesel Exhaust Fluid (urea solution) injected into the SCR system to reduce NOx.

Diesel Particulate Filter — traps soot from diesel exhaust and burns it off during regeneration.

Electronic Braking System — electronically controlled air brakes common on modern heavy trucks.

Engine (or electronic) Control Module — the computer that runs fuel, timing, and many fault monitors.

Exhaust Gas Recirculation — routes exhaust into the intake to lower combustion temperatures and NOx.

Evaporative Emission Control — captures fuel vapors from the tank so they are not vented to air.

Fuel Tank Pressure sensor — measures EVAP system pressure/vacuum during leak monitors.

Mass Air Flow sensor — measures intake air mass so the ECM can meter fuel.

Engine Coolant Temperature sensor — tells the ECM how hot the coolant is for fueling and fan strategy.

Short-Term and Long-Term Fuel Trim — ECM corrections that add or remove fuel to hold stoichiometry.

Failure Mode Identifier — on J1939, the number that says how a parameter failed (open, short, high, low…).

SAE network protocol used on heavy trucks for SPN/FMI diagnostic messages between modules.

Nitrogen oxides — combustion gases that SCR systems are designed to reduce.

On-Board Diagnostics II — the light-vehicle standard for P/B/C/U fault codes and freeze-frame data.

Selective Catalytic Reduction — aftertreatment that uses DEF over a catalyst to cut NOx.

Suspect Parameter Number — on J1939, the ID of the parameter that set a fault (often paired with an FMI).

Transmission Control Module — the computer that commands shifts, ratios, and many transmission protections.

Vehicle Identification Number — the 17-character factory ID that encodes make, model year, and plant data.

Cylinder bank on a multi-bank engine. Bank 1 is the bank that includes cylinder 1. On an inline engine there is usually one bank; on a V6/V8 each bank has its own upstream/downstream O2 sensors and often its own catalyst (e.g. P0420 vs P0430). Crankcase ventilation is shared—not one PCV/CCV per bank.