📚 Vehicle Manual Information

1991 Audi A6 (C4-4A) Service and Repair Manual

🏷️ Basic Information

Make:

Audi

Model:

A6

Year:

1991

Chassis Code:

C4

Body Code:

4A

👋 Introduction

Vehicle Segment:

Executive Sedan/Wagon

Competitors:

BMW 5 Series, Mercedes-Benz E-Class, Volvo 900 Series, Jaguar XJ.

Design Philosophy:

Understated luxury, strong Quattro all-wheel-drive capabilities, refined engineering, comfortable touring.

Manual Value Proposition:

Provides technicians and knowledgeable DIY enthusiasts with the critical, manufacturer-specific information needed for accurate and efficient maintenance and repair of the 1991 Audi A6.

📋 Manual Details

All Models And Trims:

Yes

Repair Scope:

A-Z (all repairs)

Type:

Service and Repair Manual

Authenticity:

Dealer-Technician Equivalent

Language:

English

Format:

Likely Printed (common for era); PDF versions may exist but this product is described as the original dealership manual.

📖 Manual Coverage

Engine:

Complete overhaul, tuning, diagnostics, fuel injection, ignition, exhaust, cooling, lubrication, engine management systems.

Transmission:

Manual and automatic transmission repair, overhaul, fluid service, diagnostics, driveline components (CV joints, driveshafts).

Brakes:

Hydraulic system, ABS (Anti-lock Braking System), disc and drum brake service, parking brake, fluid replacement.

Steering:

Power steering system, steering rack, linkage, wheel alignment procedures.

Suspension:

Front and rear suspension components (struts, shock absorbers, control arms, ball joints, bushings), wheel bearing replacement.

Electrical:

Full wiring diagrams, lighting, starting and charging system, battery service, fuses, relays, diagnostic codes, power accessories.

Bodywork:

Body panel repair, door mechanisms, interior trim, climate control system (HVAC), body electrical components, glass replacement.

Fuel:

Fuel tank, fuel pump, fuel lines, fuel injectors, evaporative emissions control (EVAP).

Cooling:

Radiator, thermostat, water pump, coolant hoses, cooling fan, system diagnostics.

Maintenance:

Scheduled maintenance, oil changes, filter replacements, tune-ups, belt replacement, fluid checks and changes.

Diagnostics:

Troubleshooting guides, symptom-based diagnostics, fault code interpretation (OBD-I era).

Repair:

Step-by-step repair procedures for all major components and systems, including full engine and transmission rebuilds.

Installation:

Procedures for replacing or installing parts and components.

Specifications:

Torque specifications, clearances, fluid capacities, electrical specifications, diagnostic parameters.

Depth:

Comprehensive: Covers everything from basic maintenance to complex internal component repair and system diagnostics.

Detail Level:

Expert-level detail, including specialized tools and techniques required for specific Audi repairs.

📊 Manual Specifications

Digital Format Quality:

N/A (Assumed printed original, but if PDF, expect high resolution scans of original pages with searchable text if OCR applied).

Print Quality Original:

High quality, professional printing typical of OEM service manuals.

Binding Type Original:

Likely perfect bound or spiral bound for ease of use during repairs.

Paper Type Original:

Durable, high-quality paper stock designed to withstand workshop environments.

⚙️ Engine Specifications

Engine Family:

Volkswagen Group EA827 (modified) / VW/Audi V6

Engines:

2.0L (5-cylinder, 20-valve turbo - 3B, RR), 2.3L (5-cylinder, 10-valve - NG, 7A), 2.6L (V6, 12-valve - ABC), 2.8L (V6, 12-valve - AAH), 2.8L (V6, 12-valve - AHC/ACK - later models, less likely for 1991 C4)

Horsepower Range:

Approximately 115 hp (2.3L) to 230 hp (20V Turbo)

Torque Range:

Approximately 132 lb-ft (2.3L) to 243 lb-ft (20V Turbo)

Fuel Injection Type:

Bosch Motronic electronic fuel injection (EFI) across most variants.

Fuel Grade:

Unleaded gasoline (Octane rating specified by engine variant, typically 91 RON / 87 AKI or higher for turbo models).

🔧 Transmission

Type:

5-speed Manual Transmission

Type:

4-speed Automatic Transmission (ZF 4HP-22 or similar)

Drivetrain:

Front-wheel drive (FWD) or Audi Quattro permanent all-wheel drive (AWD).

Automatic Transmission Fluid:

Dexron III or equivalent specified by Audi for the era.

Manual Transmission Fluid:

API GL-4 or GL-5 gear oil, specific viscosity (e.g., 75W-90 or 80W-90) as per Audi specs.

📐 Dimensions

Body Styles:

4-door Sedan, 5-door Avant (Wagon)

Wheelbase Mm:

Approximately 2700 mm (106.3 in)

Length Mm:

Approximately 4780-4800 mm (188.2-189.0 in)

Width Mm:

Approximately 1780-1790 mm (70.1-70.5 in)

Height Mm:

Approximately 1420-1450 mm (55.9-57.1 in)

Curb Weight Kg:

Approximately 1450-1650 kg (3197-3638 lbs), depending on engine and drivetrain.

Gross Vehicle Weight Rating Kg:

Specified per model variant, typically around 2000-2150 kg.

🛡️ Safety Features

NHTSA Crash Test Ratings:

Not readily available for this model year and era from standardized testing bodies as we know them today.

ABS:

Standard on most models, optional on base variants. Detailed diagnostic and repair procedures are expected in the manual.

Quattro AWD:

Provides enhanced traction and stability, particularly in adverse conditions.

Airbags:

Driver-side airbag standard on most trims, passenger airbag optional or not available on all variants for 1991.

Seat Belts:

Front and rear seat belts, with pre-tensioners on front belts in some configurations.

Body Construction:

Unitary body construction with integrated safety cage and crumple zones.

💡 Technology Features

Audio System:

Factory AM/FM cassette player, often with premium sound system options (e.g., Bose).

Navigation:

Rare or optional on very late C4 models, generally not standard for 1991. GPS navigation was nascent.

ABS:

As mentioned in safety, ABS was a key driver assistance feature for its time.

Cruise Control:

Standard or optional depending on trim level.

Phone Integration:

Not applicable in the modern sense; some vehicles had optional early car phone provisions.

🔧 Maintenance

Oil Change Interval:

Typically 7,500 - 10,000 miles (12,000 - 15,000 km) or 12 months, whichever comes first. Specifics vary by engine and driving conditions.

Timing Belt Replacement:

Critical for 5-cylinder and V6 engines. Interval typically 60,000 - 90,000 miles (96,000 - 145,000 km). Failure can cause severe engine damage.

Spark Plug Replacement:

Varies by plug type, typically 30,000 - 60,000 miles.

Engine Oil Type:

API SG/SH or higher. Viscosity typically 0W-40, 5W-30, 5W-40, 10W-40, or 10W-30 depending on climate and engine, per owner's manual recommendations.

Coolant Type:

Ethylene glycol-based antifreeze (G11 or G12 specification) mixed with distilled water (50/50 ratio).

Brake Fluid Type:

DOT 3 or DOT 4 brake fluid.

Fuel Economy:

Can be a concern for some, especially earlier 5-cylinder engines and AWD models.

Electrical Gremlins:

Aging wiring harnesses, faulty grounds, and degraded sensor connections can lead to intermittent electrical issues.

Suspension Wear:

Control arm bushings, ball joints, and tie rods are common wear items due to age and mileage.

Cooling System:

Plastic coolant expansion tanks can become brittle and crack; water pump seals can fail.

Climate Control Actuators:

Vacuum or electric actuators for HVAC flaps can fail, leading to improper airflow or temperature control.

Oil Leaks:

Valve cover gaskets, oil pan gaskets, and front/rear main seals can degrade with age.

📚 Vehicle History

Audi Legacy:

Audi has a long history of engineering innovation, particularly with quattro all-wheel drive and pioneering advancements in automotive technology and design.

C4 Platform:

The C4 platform (Type 4A) represented a significant evolution from the C3 (Type 44). It featured a more modern, aerodynamic design and introduced a wider range of engine options, including the V6 and 20-valve inline-5 turbo.

A6 Naming Convention:

The 1991 model marked the introduction of the 'A6' designation, replacing the previous 'Audi 100' nameplate in many markets, aligning with Audi's new naming strategy to signify its position in the model hierarchy.

Production Years:

The C4 platform was produced from 1990 to 1997 (though the A6 name was adopted earlier).

Manufacturing Location:

Primarily Ingolstadt, Germany, and Neckarsulm, Germany.

🏆 Awards & Recognition

General Reputation:

The Audi 100/A6 range was generally well-regarded for its build quality, comfort, and the pioneering of quattro technology. Specific awards for the 1991 model are less documented than for later generations, but it contributed to Audi's reputation for engineering excellence in the luxury segment.