Smart Fortwo W451 100F | Intermittent No Start | Starter Generator Slip Ring Test | Part 2

In Part 2 of this real workshop case on a Smart Fortwo W451, I demonstrate exactly why this vehicle was suffering from an intermittent no-start fault — and why this type of fault is one of the most difficult to diagnose. After removing the faulty starter generator, I show you how the contact resistance between the slip rings and carbon brushes changes dramatically depending on which position the rotor has stopped at. At certain rotor positions the resistance measured 178 kilo-ohms — far too high for the rotor winding to be properly excited, meaning the magnetic field cannot be created and the engine will not crank. I also inspect and test the refurbished replacement unit supplied by the fleet company, and record the resistance readings on camera as documented evidence before installation — something every technician should do when fitting a customer or company-supplied part. Finally, I install the refurbished starter generator and carry out a live start test, confirming the intermittent no-start fault has been resolved. ✅ What you will learn in this video: How slip ring and carbon brush contact resistance causes intermittent no-start faults on the Smart Fortwo W451 Why the rotor stop position is critical to diagnosing this fault correctly How to test starter generator slip ring resistance with a multimeter Why you must document and record parts supplied by a customer or company before fitting them How the N129 control unit excites the rotor winding to create a magnetic field and crank the engine 🔧 Vehicle: Smart Fortwo W451 🔧 Fault: Intermittent No Start 🔧 Root Cause: High resistance at starter generator slip rings and carbon brushes due to rotor stop position and wear 🔧 Fix: Starter generator replacement 📺 Watch the full series: ▶ Part 1 — [add your Part 1 link here] ▶ Part 2 — You are watching this now ▶ Part 3 — Coming soon 👍 If this video helped you, please like, share, and subscribe — it helps the channel grow and helps other technicians find this content. #️⃣ HASHTAGS #SmartFortwo #SmartForTwo451 #W451 #StarterGenerator #IntermittentNoStart #SlipRing #CarbonBrush #AutoElectrics #AutomotiveDiagnostics #CarRepair #IMITechSafe #SmartCar #SmartRepair #CarDiagnostics #MechanicLife #WorkshopLife #AutoRepair #AutomotiveEducation #StanhopeAutoRepair #SmartFortwoProblem ⚠️ DISCLAIMER The repair, testing, and procedures shown in this video are carried out by a qualified automotive technician holding IMI TechSafe certification in Hybrid & Electric Vehicle Technology, Level 3 City & Guilds qualifications in Auto Electrics, and Car & Light Goods Vehicle Inspection. This video is intended for educational and informational purposes only. Working on automotive electrical systems, including starter generators, involves risks that can cause serious injury if handled incorrectly. Do not attempt any of the procedures shown in this video unless you hold the relevant qualifications and are trained to work safely on automotive electrical systems. The refurbished starter generator installed in this video was supplied by the fleet company and fitted under their instruction. Resistance test results were recorded on camera prior to installation as documented evidence. No liability is accepted by the technician or Stanhope Auto Repair Centre Wardak for the condition or future performance of customer or company-supplied parts. Always follow manufacturer procedures, safety guidelines, and your local regulations when working on any vehicle.