🏷️ Basic Information

Make:

BMW

Model:

850i

Chassis Code:

E31

Model Year:

1991

Product Name:

BMW 850i (E31) 1991 Electrical TROUBLESHOOTING Manual

Manual Focus:

Electrical Troubleshooting

👋 Introduction

Positioning:

Flagship Grand Tourer (GT) representing BMW's luxury and performance pinnacle of the era.

Target Audience:

Affluent individuals seeking a sophisticated, high-performance, and technologically advanced luxury coupe.

Competitors:

Porsche 928, Mercedes-Benz SL-Class (R129), Jaguar XJS, Aston Martin DB7 (later models).

Design:

Striking, aerodynamic coupe styling with a long hood, short deck, and a distinctive shark-nose front end.

Engine:

Powerful V12 engine, a rarity in its class and time.

Technology:

Advanced for its time, featuring sophisticated electronics, climate control, and luxury appointments.

Value:

Crucial for diagnosing and repairing the complex electrical systems that define the E31's luxury and performance features.

📋 Manual Details

Primary Coverage:

Electrical Systems and Troubleshooting

Secondary Coverage:

Power Distribution, Fuses, Grounding, Engine Control, Charging, Starting, Transmission Control, SRS, ABS, Power Accessories, Lighting, Climate Control, Infotainment, Cruise Control, Security, On-Board Computer

Estimated Page Count:

Likely 200-400 pages (typical for comprehensive electrical manuals)

Type:

Specialized Technical Manual / Electrical Troubleshooting Manual

Language:

English

Format:

PDF (assumed, common for digital sales)

📖 Manual Coverage

Engine Management:

Engine Control System (DME - Digital Motor Electronics)

Charging Starting:

Charging System, Start System

Transmission:

Electronic Transmission Control (EGS - Elektronische Getriebesteuerung)

Safety Systems:

Supplemental Restraint System (SRS), Slip Control ABS (Anti-lock Braking System)

Comfort Convenience:

Power Mirrors, Central Locking Module, Power Windows, Power Seats, Heated Seats, Power Sun Roof, Horn

Wipers Washers:

Wiper/Washer Module, Headlight Washer, Windshield Washer Jet Heaters

Instrumentation:

Instrument Cluster, Multi-Function Clock

Lighting:

Light Switch Details, Headlights/Fog Lights, Turn/Hazard Lights, Park/Tail/Underhood Lights, License Plate/Luggage Compartment Lights, Back-up Lights, Brake Lights, Interior Lights, Glove Box Light/Cassette Box Ashtray Lights/Charging Socket

Climate Control:

Park Ventilation with HKR (Heated Control), Rear Window Defogger, Integrated Climate Regulation

Infotainment:

Radio/CD Player, Radio/Hi-Fi, Cellular Telephone

Driver Aids:

Cruise Control (Tempomat)

Security:

Anti-Theft System

Information Systems:

On-Board Computer

Electrical Distribution:

Power Distribution Chart, Fuse Chart, Power Distribution Details, Ground Distribution

Diagnostic Ports:

Data Link

Component Locations:

Component Location Chart, Component Location Views

Wiring Details:

Splice Location Views, Connector Views

Troubleshooting Methodology:

Systematic diagnostic procedures, symptom-based troubleshooting, wiring diagram interpretation, component testing

Diagnostic Tools:

Guidance on using multimeters, oscilloscopes, and BMW-specific diagnostic equipment (if applicable for the era)

Component Testing:

Procedures for testing individual electrical components, relays, switches, sensors, and actuators

Wiring Diagrams:

Interpretation and use of detailed electrical schematics

Fuse Relay Identification:

Identification, testing, and replacement of fuses and relays

Ground Point Verification:

Locating and testing ground points for electrical continuity

Connector Inspection:

Inspection and repair of electrical connectors for corrosion or damage

Depth:

Advanced Diagnostic and Repair

Focus:

Detailed electrical system diagnostics, fault finding, and repair procedures

📊 Manual Specifications

Format:

PDF

Searchability:

Likely Searchable Text (if digitally produced)

Quality:

High-resolution schematics and diagrams (essential for electrical work)

Binding:

N/A (for digital format)

Paper Type:

N/A (for digital format)

⚙️ Engine Specifications

Engine Code:

M70

Configuration:

V12

Displacement:

5.0 Liters (4988 cc)

Bore X Stroke:

84.0 mm x 75.0 mm

Compression Ratio:

8.8:1

Horsepower:

296 hp (221 kW) @ 5200 rpm

Torque:

332 lb-ft (450 Nm) @ 4100 rpm

Induction:

Naturally Aspirated, Bosch Motronic DME (Digital Motor Electronics) with two ECUs (one per cylinder bank)

Fuel Type:

Premium Unleaded Gasoline (91+ Octane)

Ignition System:

Distributorless Ignition System (DIS) with two ignition coils

🔧 Transmission

Type:

4-Speed Automatic (4HP33)

Type:

6-Speed Manual (Rare, primarily for specific markets)

Electronic Control:

Electronic Gearbox Control (EGS)

Automatic Transmission Fluid:

BMW ATF LT-2 or equivalent (e.g., Dexron III)

📐 Dimensions

Length:

191.1 in (4854 mm)

Width:

71.8 in (1824 mm)

Height:

52.5 in (1333 mm)

Wheelbase:

107.9 in (2740 mm)

Curb Weight:

Approx. 4,145 lbs (1880 kg)

Gross Weight Rating:

Approx. 5,115 lbs (2320 kg)

🛡️ Safety Features

Crash Test Data:

No formal US crash test ratings from NHTSA or IIHS for this era, but German TUV tested. Known for robust body structure.

Braking System:

Four-wheel disc brakes, ABS (Anti-lock Braking System)

Traction Control:

Optional ASC (Automatic Stability Control) or ASC+T (with Traction Control) on later models/transmissions, but not standard on early 1991 850i.

Airbags:

Driver's airbag standard

Seat Belts:

Pre-tensioned front seat belts

Structure:

Reinforced passenger cell

💡 Technology Features

Audio System:

BMW Hi-Fi system, optional CD player and upgraded sound systems (e.g., Harman Kardon).

User Interface:

Centralized control for many functions, including climate, audio, and OBC. Often operated via buttons and a rotary dial.

Cruise Control:

Standard 'Tempomat' cruise control system.

Parking Aid:

No factory rear parking sensors on this model year.

Cellular Telephone:

Optional integrated cellular telephone system.

Features:

On-Board Computer (OBC) providing data on fuel economy, range, speed, and various system checks.

🔧 Maintenance

Oil Change Interval:

Every 7,500 - 10,000 miles (12,000 - 16,000 km) or annually, depending on usage and oil quality. BMW Condition Based Service (CBS) system on later models, but manual is pre-CBS.

Transmission Fluid Change:

Recommended every 50,000 - 60,000 miles (80,000 - 100,000 km), though often considered a 'lifetime' fluid by manufacturers of the era.

Engine Oil Type:

BMW High Performance Synthetic 5W-30 or 5W-40 (e.g., Castrol TWS Motul 5W-40)

Engine Oil Capacity:

Approx. 7.0 Liters (7.4 US Quarts) with filter change

Coolant Type:

BMW Blue Antifreeze/Coolant (G48 ethylene glycol based) mixed 50/50 with distilled water

Brake Fluid Type:

DOT 4

Electrical Gremlins:

Common issues include ABS/ASC warning lights, erratic gauge readings, and non-functional accessories due to failing wiring harnesses, modules, or grounds.

V12 Specific:

Throttle position sensors, idle control valves, and dual DME failures can occur. Spark plug replacement (12 plugs) can be labor-intensive.

HVAC Climate Control:

Climate control module failures, blower motor resistor issues, and vacuum leaks affecting blend doors.

Wiring Harnesses:

Regular inspection of wiring harnesses, especially in engine bay and near heat sources, for degradation.

Grounds:

Ensure all ground points are clean and tight to prevent electrical faults.

Battery Health:

Maintain a robust battery and ensure clean terminals, as voltage drops can cause system malfunctions.

📚 Vehicle History

Bmw Heritage:

BMW's legacy of engineering excellence, performance, and luxury motor vehicles.

E31 Introduction:

Introduced in 1989 as a successor to the E24 6 Series, aiming to compete with established luxury GTs.

E31 Distinctiveness:

First BMW coupe to feature a V12 engine, pop-up headlights, and a multi-link front suspension.

E31 Engines:

Initially launched with the 5.0L M70 V12. Later models (1993 onwards) received the 5.6L S70 V12 (850CSi) and the V8 M60/M62 (840Ci).

Production Years:

1989–1999

Production Locations:

Dingolfing, Germany

Total Units Produced:

Approximately 30,621 units across all variants.

🏆 Awards & Recognition

Automotive Press:

Consistently praised by automotive press for its styling, V12 engine, and luxurious GT capabilities. Often featured in 'best GT' lists of its era.

Collectible Status:

Considered a modern classic and a desirable collectible due to its unique V12 engine and timeless design.