The 1991 Audi 100 represents a significant entry in the executive sedan segment, embodying Audi's reputation for premium quality and advanced engineering. Built on the robust C4 platform, this model is characterized by its aerodynamic styling and high-quality interior materials, offering a comfortable and refined driving experience. Available with front-wheel drive or the renowned quattro all-wheel drive system, and powered by a range of engines including a 2.8L V6, the Audi 100 was designed to compete with leading luxury vehicles of its era, emphasizing performance and sophisticated design. This comprehensive factory service manual provides detailed guidance for the maintenance, repair, and diagnostics of the 1991 Audi 100. It covers all major systems, including the powertrain, chassis, body, and electrical components, offering in-depth procedures from routine scheduled maintenance to complete component overhauls. The manual is an essential resource for owners, technicians, and mechanics, detailing technical specifications, troubleshooting steps, and specific maintenance requirements to ensure the optimal performance and longevity of the vehicle. 🏷️ Basic Information Identification Make: Audi Model: 100 Year: 1991 Codes Chassis Code: C4-4A 👋 Introduction Market Position Segment: Executive Sedan / Luxury Mid-size Sedan Brand Perception: Premium, advanced engineering, quattro all-wheel drive reputation Competitive Analysis Key Competitors 1991: BMW 5 Series (E34), Mercedes-Benz E-Class (W124), Lexus LS 400 (though higher segment), Cadillac DeVille Key Features Drivetrain Options: Front-wheel drive (FWD) and permanent all-wheel drive (quattro) Platform Design: C4 platform, known for robust construction and aerodynamic styling Interior Quality: High-quality materials, ergonomic design, advanced features for its time 📋 Manual Details Coverage Areas All Models Variants: Yes Repair Scope: A-Z (All Repairs) Page Count Estimated Pages: Extensive (typical for factory service manuals, often 1000+ pages) Manual Type Type: Factory Service Manual (FSM) Language Language: English Format Format: PDF Download 📖 Manual Coverage Systems Covered Powertrain: Engine mechanical, engine electrical, fuel system, ignition system, exhaust system, transmission (manual and automatic), drivetrain, clutch Chassis: Suspension (front and rear), steering system, braking system (including ABS), wheels and tires Body And Interior: Body construction, exterior trim, doors, windows, interior trim, seats, climate control system (HVAC), audio system Electrical And Electronics: Wiring diagrams, lighting, instruments, charging system, starting system, power accessories, control modules, diagnostic trouble codes (DTCs) Procedures Included Maintenance: Scheduled maintenance, fluid changes, filter replacements, lubrication, inspections Repair And Rebuild: Engine overhaul, transmission overhaul, component replacement, system diagnostics, electrical repairs, body panel repair Diagnostics And Troubleshooting: Step-by-step diagnostic procedures, fault finding charts, symptom-based troubleshooting Technical Depth Depth: Comprehensive; covers basic maintenance to complete engine and transmission rebuilds, including detailed electrical schematics and diagnostic procedures 📊 Manual Specifications File Format Digital Format: PDF Print Quality Scan Quality: High-resolution (assumed, based on description of dealership use) Binding Type Binding: N/A (Digital PDF Download) Paper Type Paper Quality: N/A (Digital PDF Download) ⚙️ Engine Specifications Primary Engine 1 Engine Code And Type: AAH (2.8L SOHC V6 90°) Displacement Liters: 2.8 Horsepower Ps: 172 PS @ 5500 rpm (approximate, varies slightly by market/spec) Torque Nm: 245 Nm @ 3000 rpm (approximate) Fuel System: Bosch Motronic fuel injection (typically Motronic M2.3 or M2.4) Ignition System: Electronic ignition with distributor Valve Train: SOHC (Single Overhead Camshaft) per bank, 2 valves per cylinder Other Available Engines Engine Options: 5-cylinder gasoline engines (e.g., 2.3E, 2.3E-20V), 5-cylinder diesel engines (e.g., 2.5 TDI), 2.2L 5-cylinder gasoline (prior to C4 in some markets), potentially turbo variants in some regions (e.g., S4 variants). 🔧 Transmission Standard Transmission Options: 5-speed manual transmission Optional Transmission Options: 4-speed automatic transmission (ZF 4HP22 or similar) Features AWD System: Torsen T-3 center differential for quattro models, typically with rear open differential (early models) or optional rear limited-slip differential (LSD). Maintenance Manual Transmission Fluid Spec: API GL-4 or GL-5, SAE 75W-90 (Check manual for exact spec) Automatic Transmission Fluid Spec: G 052 162 A1 (or equivalent Dexron-III compatible fluid, consult manual for specific Audi specification) 📐 Dimensions Exterior Length Mm: 4787 mm (approx.) Width Mm: 1778 mm (approx.) Height Mm: 1430 mm (approx.) Weights Curb Weight Kg: 1450 - 1600 kg (depending on engine and drivetrain) Gross Vehicle Weight Rating Kg: Approx. 2000 - 2150 kg Cargo Trunk Volume Liters: Approximately 550 liters (sedan) 🛡️ Safety Features Ratings Crash Test Data Availability: Limited public data for 1991 models, but designed to meet European safety standards of the era. Active Features ABS: Anti-lock Braking System (ABS) available/standard on many models Traction Control: Traction Control System (ASR - Automatic Slip Regulation) available on some quattro models Passive Features Airbags: Driver-side airbag standard on many models, passenger airbag optional or unavailable depending on market and configuration. Seatbelts: Front and rear seatbelts, pre-tensioners for front seatbelts on some models Body Structure: Integrated safety cage, crumple zones 💡 Technology Features Infotainment Audio System: Factory AM/FM stereo cassette player, optional CD player, often with premium speaker systems (e.g., Bose on higher trims). Climate Control Tech: Manual or...