| A/F | Air/Fuel ratio |
| AAM | Alliance of Automobile Manufacturers |
| AAMA | American Automobile Manufacturers Association |
| ABC | Active Body Control |
| ABS | Antilock Brake System |
| ABOT | Aluminum Beaker Oxidation Test |
| AC | Alternating Current |
| A/C | Air Conditioning |
| ACC | Adaptive Cruise Control |
| ACC | Automatic Climate Control |
| ACEA | Association des Constructeurs Européens d’Automobiles |
| ACERT | Advanced Combustion Emission Reduction Technology (Caterpillar) |
| ACM | Airbag Control Module |
| ADAS | Advanced Driver Assistance System |
| AECM | Airbag Electronic Control Module |
| AFC | Adaptive Fuel Control |
| AFC | Air Flow Control |
| AFC | Air Fuel Control |
| AFNOR | Association Français de Normalisation |
| AFR | Air Fuel Ratio |
| AFS | Advanced Frontlighting System |
| AGMA | American Gear Manufacturer’s Association |
| AH | Polycyclic Aromatic Hydrocarbons |
| AHEM | Association of Hydraulic Equipment Manufacturers |
| AHLD | Automatic Headlamp Leveling Device |
| AHR | Active Head Restraint |
| AHRS | Amp Hours |
| AHS | Active Handling System |
| AIAM | Association of International Automobile Manufacturers |
| AIChE | American Institute of Chemical Engineers |
| AK | AntiKnocks |
| ALFA | Anonima Lombarda Fabbrica Automobili. When Nicola Romeo bought ALFA in 1915, his surname was appended. |
| ALR | Automatic Locking Retractor |
| ALS | Adaptive Lighting System |
| ALT | Alternator (replaced with GEN) |
| AMB | Ambient |
| AMG | Aufrecht Melcher Großaspach |
| AMM | Air Mass Meter |
| AMP | Amplifier |
| AMPS | Amperes or Amperage |
| AN | Acid Number |
| ANSI | American National Standards Institute |
| AO | AntiOxidant |
| AOCS | American Oil Chemists’ Society |
| APDF | Advanced Petroleum Based Fuels |
| APE | Association of Petroleum Engineers |
| API | American Petroleum Institute |
| API SJ | API motor oil quality level for 2001 and older automotive engines |
| API SL | API motor oil quality level for 2004 and older automotive engines |
| API SM | API motor oil quality level for 2010 and older automotive engines |
| API SN | API motor oil quality level first licensed October 1, 2010 |
| ARS | Adaptive Receptive System |
| ARS | Automatic Restraint System |
| ARS | Adaptive Rearlighting System |
| ASARC | Air Suspension Automatic Ride Control |
| ASD | Automatic Shutdown |
| ASG | Automatic-Shift Gearbox |
| ASME | American Society of Mechanical Engineers |
| ASSYST | Active Service System |
| ASTC | Automatic Stability and Traction Control |
| ASTM | American Society for Testing and Materials |
| A/T | Automatic Transmission/Transaxle |
| ATC | Active Traction Control |
| ATC | Technical Committee of Petroleum Additive Manufacturers in Europe |
| ATF | Automatic Transmission Fluid |
| ATF | Automatic Transfer Case |
| ATIEL | Association Technique de I’IndustrieEuropéenne des Lubrifiants (European Oil Marketers Association) |
| AT-PZEV | Advanced Technology Partial Zero Emission Vehicle |
| ATV | All-Terrain Vechicle |
| ATX | Automatic Transaxle |
| AW | Anti-Wear |
| AWD | All-Wheel Drive |
| AYC | Active Yaw Control |
| AXOD | Automatic Overdrive Transaxle |
