Vehicle diagnostics glossary

OBD

On-Board Diagnostics: the vehicle's self-diagnosis, which monitors emissions and faults and makes them available through a standard socket.

OBD-II and EOBD

The US (OBD-II) and European (EOBD) versions of emissions diagnostics, with common services and codes defined in SAE J1979 and ISO 15031.

WWH-OBD

World-Wide Harmonized OBD (ISO 27145): harmonized emissions diagnostics that runs over UDS, on CAN or DoIP.

SAE J1962

The standard for the 16-pin diagnostic socket and which signal goes on each pin; pin 16 carries battery voltage.

UDS

Unified Diagnostic Services (ISO 14229): the protocol modern ECUs use to read faults and data, and to be coded and programmed.

KWP2000

Keyword Protocol 2000 (ISO 14230): the diagnostic protocol that came before UDS, typical of K-Line and the first ECUs on CAN.

DTC

Diagnostic Trouble Code: the fault code an ECU stores when it detects a failure, with its status (pending, confirmed or historical).

Freeze frame

The vehicle's conditions (engine speed, temperature, load) at the moment a fault was stored.

Readiness monitors

They show whether the vehicle has completed its emissions self-tests since the last clear.

Mode 06

OBD service 06: the on-board test results for each monitor, with their limits; it lets you see a fault before the warning light comes on.

ECU

Electronic Control Unit: the electronic control unit for one of the vehicle's systems, such as the engine, gearbox or brakes.

Gateway

The ECU that links the vehicle's buses to the diagnostic socket and filters what passes between them; some manufacturers require authentication to write.

CAN

Controller Area Network (ISO 11898): the communication bus between ECUs; OBD diagnostics runs over it on pins 6 and 14.

CAN FD

CAN with Flexible Data-rate: the evolution of CAN, with frames of up to 64 data bytes and a faster data phase.

ISO-TP

ISO 15765-2: the transport layer that splits long diagnostic messages into CAN frames and puts them back together.

DoIP

Diagnostics over Internet Protocol (ISO 13400): diagnostics over automotive Ethernet, on pins 3, 11, 12 and 13 with activation through pin 8.

K-Line

The single-wire serial line on pin 7 (ISO 9141-2 and ISO 14230) used to diagnose cars before CAN.

L-Line

The line on pin 15 that some cars use only to wake the ECU when starting communication over K-Line.

SW-CAN

Single Wire CAN (SAE J2411), or GMLAN: GM and Opel's single-wire CAN on pin 1, at 33.3 kbit/s and 83.3 kbit/s for programming.

J1939

The family of SAE CAN standards for trucks, buses and machinery, with 29-bit identifiers and numbered parameters (SPN).

DM1

The J1939 message each ECU uses to broadcast its active faults, each with its SPN and FMI, plus the status of its warning lamps.

TP2.0

The diagnostic transport over CAN that the Volkswagen group used before adopting ISO-TP.

VIN

Vehicle Identification Number (ISO 3779): the 17-character chassis number that many ECUs store and diagnostics can read.

Pass-thru

An interface between the PC and the vehicle's socket that lets the manufacturer's or a third party's software talk to the ECUs.

SAE J2534

The Windows pass-thru programming interface that manufacturers' software uses to diagnose and reprogram.

D-PDU API

ISO 22900-2: the standard programming interface between diagnostic software and the vehicle interface (MVCI).

RP1210

TMC's recommended practice for the interface between the PC and heavy vehicles, used by truck diagnostic software.

ODX

Open Diagnostic data eXchange (ISO 22901): the data format that describes how to diagnose each ECU: services, parameters and faults.

Seed & key

An ECU's security challenge before it can be coded or programmed: it sends a seed and waits for the key calculated by authorized software.

Coding

Changing an ECU's configuration (equipment, variants, learned values) without changing its software.

Flashing

Replacing an ECU's software with another version, usually a manufacturer update.

Remote session

In Diaglana, the connection between a vehicle and a workshop through the platform, which starts when the driver authorizes it with the device's button.

MIL (check engine light)

Malfunction Indicator Lamp: the engine warning light on the dashboard. Steady, it signals a fault that affects emissions; flashing, misfires that can damage the catalytic converter.

Misfire

A cycle in which a cylinder does not burn its mixture properly. It is stored as P0300 (several cylinders) or P0301-P0312 (a specific cylinder).

Oxygen sensor (lambda)

The exhaust oxygen sensor: it measures the oxygen left in the gases so the ECU can adjust the mixture; the one behind the catalytic converter checks how well it works.

Catalytic converter

The exhaust part that turns the most harmful gases into less harmful ones; the ECU checks its efficiency with the oxygen sensors (P0420, P0430).

EGR

Exhaust Gas Recirculation: the valve that sends part of the exhaust gas back to the intake to lower the combustion temperature and the nitrogen oxides (NOx).

DPF

Diesel Particulate Filter: it traps the soot of diesel engines, and of some gasoline ones (GPF), and burns it off during regenerations.

Regeneration

The controlled burning of the soot collected in the particulate filter, at high temperature; the car does it by itself while driving and needs a few minutes without interruption.

SCR / DEF (AdBlue)

Selective Catalytic Reduction: the catalyst that reduces the NOx of diesel engines by injecting diesel exhaust fluid (AdBlue), a 32.5% urea solution kept in its own tank.

NOx sensor

It measures the nitrogen oxides in the exhaust before or after the SCR; the ECU uses it to dose the fluid and check that the system works.

MAF sensor

Mass Air Flow: the sensor that measures the mass of air entering the engine so the ECU can work out how much fuel to inject.

MAP sensor

Manifold Absolute Pressure: the intake manifold pressure sensor; on turbocharged engines it also measures the boost pressure.

Throttle body

The motorized valve that controls the air entering the engine according to the pedal; when it fails, the ECU usually limits power.

CKP and CMP sensors

The crankshaft (CKP) and camshaft (CMP) position sensors: they tell the ECU the engine speed and position so it can inject and ignite on time.

EVAP

The system that collects the fuel vapors of the tank in a charcoal canister and burns them in the engine; a leak or a loose fuel cap gives codes P0440-P0457.

Limp mode

The protective operation in which the ECU limits power or engine speed after detecting a fault, so that the car can still reach a shop.

BMS

Battery Management System: the electronics that monitor a battery's voltage, current, temperature and state of charge; on the 12 V battery it is usually a sensor on the negative terminal.

Have a specific code, such as P0420? What it means, its causes and whether you can keep driving: Fault codes

Frequently asked questions

Keep reading

• Remote OBD diagnostics: what it is, how it works and what it can't do
• CAN and CAN FD in diagnostics (ISO 15765)
• DoIP (ISO 13400): diagnostics over Ethernet
• Pass-thru interface: SAE J2534, D-PDU and RP1210
• OBD fault codes: what each one means