🏷️ Basic Information Identification Make: GMC Model: Sonoma Year: 1991 Codes Platform Code: GMT400 (early generation) 👋 Introduction Market Position Market Position: Targeted at DIY enthusiasts and independent repair shops seeking authoritative, factory-derived information for the 1991 GMC Sonoma. Competitive Analysis Competitive Analysis: Offers a modern, convenient, and licensed alternative to outdated printed manuals. Emphasizes ease of access and comprehensive coverage compared to generic repair guides. Key Features Key Features: Officially licensed content, OE material derivation, year-long access, multi-device compatibility, extensive system coverage, detailed diagnostic procedures. 📋 Manual Details Coverage Areas Coverage Areas: Full service and repair for 1991 GMC Sonoma Page Count Page Count: Digital access (estimated content equivalent to over 1000 pages of print) Manual Type Manual Type: Online Service and Repair Manual Software Language Language: English Format Format: Web-based software, accessible via browser 📖 Manual Coverage Systems Covered Systems Covered: Engine Mechanical, Fuel System, Cooling System, Lubrication System, Ignition System, Emission Control Systems, Clutch, Manual Transmission, Automatic Transmission, Transfer Case (if applicable), Driveshaft, Axles, Suspension (Front and Rear), Steering System, Brakes (Front and Rear), Wheels and Tires, Body (Interior and Exterior), HVAC System, Electrical System (Wiring Diagrams, Components), Lighting, Instrumentation, Audio System, Security System Engine Mechanical Coverage: Detailed information on engine disassembly, assembly, component specifications (pistons, rings, bearings, valves, camshafts), timing procedures, cylinder head refurbishment, and troubleshooting. Electrical System Coverage: Comprehensive wiring diagrams for all vehicle systems (engine control, lighting, charging, starting, accessories, HVAC). Includes component locations, testing procedures for sensors and actuators, and troubleshooting flowcharts. Procedures Included Procedures Included: Routine Maintenance, Scheduled Maintenance, Diagnosis and Troubleshooting, Component Removal and Installation, Component Reassembly and Adjustment, Torque Specifications, Fluid Capacities and Specifications, Electrical System Diagnosis, Wiring Harness Repair, Body Panel Repair, HVAC System Servicing, Brake System Bleeding and Repair, Suspension Alignment Procedures, Engine Overhaul Procedures, Transmission Service and Repair Troubleshooting Procedures: Systematic diagnostic procedures for common drivability issues, electrical faults, and mechanical problems, often presented in a step-by-step format with symptom-to-cause tables. Drivetrain Repair Procedures: Detailed steps for clutch replacement, manual transmission overhaul, automatic transmission service, differential inspection and service, driveshaft and U-joint replacement. Suspension Steering Repair Procedures: Ball joint replacement, tie rod end replacement, wheel bearing service, shock absorber/strut replacement, power steering pump and gear replacement, alignment specifications. Technical Depth Technical Depth: Comprehensive; covers everything from basic oil changes and fluid checks to advanced engine diagnostics, complete powertrain rebuilds, and detailed electrical troubleshooting. Technical Depth Engine: Deep dive into engine building and rebuilding, including machining specifications, clearances, and assembly sequences for all internal engine components. Technical Depth Electrical: In-depth electrical diagnostics, including testing of ECUs, sensors (e.g., MAP, TPS, O2 sensors), ignition coils, fuel injectors, and related wiring circuits. Troubleshooting of body control modules and accessory circuits. 📊 Manual Specifications File Format File Format: Proprietary web-based access (not a downloadable file) Accessibility: Requires internet connection and a web browser. Compatible with PC, laptop, smartphone, or tablet. Access Duration: 1 year of access included, with discounts for renewal. Print Quality Print Quality: N/A (Digital format) Binding Type Binding Type: N/A (Digital format) Paper Type Paper Type: N/A (Digital format) ⚙️ Engine Specifications Primary Engine Primary Engine: 4.3L V6 OHV (VIN 'X') Optional Engine 1 Optional Engine 1: 2.8L V6 OHV (VIN 'R') Optional Engine 2 Optional Engine 2: 2.5L I4 OHV (VIN 'T') Performance 4.3L V6 Horsepower: Approx. 160-170 hp (depending on specific configuration) 4.3L V6 Torque: Approx. 230-240 lb-ft (depending on specific configuration) Fuel System Fuel System Type: Electronic Fuel Injection (EFI) - Throttle Body Injection (TBI) for most configurations. Engine Displacements Engine Displacements Available: 2.5L (151 cu in), 2.8L (173 cu in), 4.3L (262 cu in) 🔧 Transmission Standard Transmission Standard Transmission: 4-speed Manual Transmission (NVG 4500 or similar) Optional Transmission 1 Optional Transmission 1: 4-speed Automatic Transmission (700R4/4L60) Optional Transmission 2 Optional Transmission 2: 3-speed Automatic Transmission (TH350C) on some earlier models/engines Features Transmission Fluid Spec: Dexron III (or equivalent) for automatic transmissions. Manual Transmission Fluid Spec: GL-4 gear oil (e.g., 75W-90 or 80W-90). 📐 Dimensions Exterior Wheelbase Std: Approx. 108.3 inches (2750 mm) Wheelbase Long: Approx. 117.9 inches (3000 mm) Overall Length Std: Approx. 179.8 inches (4567 mm) Overall Length Long: Approx. 195.3 inches (4960 mm) Weights Curb Weight Est: 3,500 - 4,500 lbs (1588 - 2041 kg), varies by configuration. Gross Vehicle Weight Rating Gvwr Est: 4,700 - 5,300 lbs (2132 - 2404 kg), depending on configuration. 🛡️ Safety Features Ratings Safety Ratings: NHTSA ratings from the era for this platform are generally not as detailed as modern standards. Focus on individual system integrity and maintenance for optimal safety. Active Features Active Features: Four-wheel Anti-lock Braking System (ABS) available on rear wheels, optional on front. Passive Features Passive Features: Seat belts (lap and shoulder belts for front occupants), reinforced passenger compartment. 💡 Technology Features Infotainment Infotainment System: Basic AM/FM stereo with cassette player,...