Workshop glossary
Plain-English definitions of the diagnostics protocols, standards, and shop-floor terms we deal with every day.Diagnostics & protocols
CAN bus
Controller Area Network — the two-wire serial bus that ties together every ECU in a modern car. Standardised as ISO 11898.
CAN FD
CAN with Flexible Data-rate. Same physical wiring as classic CAN but with payloads up to 64 bytes and bit rates up to 5 Mbit/s. Shipping on most cars built from around 2020.
DoIP (Diagnostics over IP)
ISO 13400. UDS diagnostic traffic carried over Ethernet rather than CAN. Standard on most premium vehicles since around 2015.
DTC
A five-character code an ECU stores when it detects a fault. Format and meaning are standardised by SAE J2012 (e.g. P0301 = misfire on cylinder 1).
ECU (Electronic Control Unit)
Any embedded computer in a vehicle. A modern car has 50–150 of them, networked over CAN/CAN FD/Ethernet, each running its own firmware.
ELM327
An OBD-II interpreter chip designed by Elm Electronics in 2005. Wraps every OBD-II protocol behind a simple AT-command serial interface and powers most consumer Bluetooth/Wi-Fi OBD adapters.
EOBD
European on-board diagnostics — the EU's emissions-driven equivalent of OBD-II, mandatory on petrol cars from 2001 and diesel from 2004. In practice EOBD and OBD-II are interchangeable for generic scanning.
Freeze frame data
A snapshot of engine sensor values captured at the exact moment a DTC was stored. Critical for diagnosing intermittent faults.
ISO 15765-4
The standard that adapts CAN bus for OBD-II / EOBD diagnostics. Mandatory on US OBD-II vehicles from model year 2008.
KWP2000
Keyword Protocol 2000 (ISO 14230). The pre-CAN diagnostic protocol used on European cars from the late 1990s up to roughly 2008.
MIL (check engine light)
The amber check-engine light. The ECU turns it on when an emissions-relevant DTC has been confirmed across two drive cycles.
OBD-II
The on-board diagnostics standard required on most cars sold in the US since 1996 and in the EU since 2001 (as EOBD). It defines how external tools read fault codes and live data from a vehicle.
PID (Parameter ID)
A numeric identifier for a single live data value the ECU exposes — engine RPM, coolant temperature, MAF reading. Defined by SAE J1979 mode 01.
SAE J1979
The SAE standard that defines OBD-II service modes (01–0A) and the list of standard PIDs every emissions-related ECU must support.
SAE J2012
The SAE standard that defines DTC structure (P/B/C/U + 4 digits) and the meaning of generic codes in the P0xxx, B0xxx, C0xxx, U0xxx ranges.
Workshop operations
Labour rate
The hourly charge-out rate a workshop bills for technician time. Varies by market, specialism, and overhead — typically £55–£140/hr in the UK, €70–€160/hr in Western Europe, $90–$180/hr in the US.
Service interval
The OEM-recommended period (time or mileage, whichever comes first) between scheduled maintenance visits. Has shifted from fixed 10,000 km to variable, oil-life-based, or condition-monitoring schedules.
Vehicle inspection
The mandatory roadworthiness check required by EU Directive 2014/45/EU and equivalent national laws. Called MOT (UK), TÜV/HU (DE), besiktning (SE), contrôle technique (FR), ITV (ES), bilsyn (DK/NO).
VIN
The 17-character identifier assigned to every vehicle since 1981. Structure is defined by ISO 3779 and decodes into manufacturer, model details, and a unique serial.
Work order
The shop-floor document — paper or digital — that captures vehicle, customer, requested work, parts, labour, and authorisation. Also called a repair order, job card, or RO.