Bad Alternator Diode causing transmission/speedometer problems

Speedometer reads 20 mph in park. Transmission output speed sensor (vehicle speed sensor) codes. Transmission will not shift (2nd gear limp mode) from a bad alternator diode. Clean, strong alternator output is critical for vehicle electrical performance. Without it, you can run into all kind of strange symptoms that you may not necessarily associate with an alternator problem, and this case study is a perfect example. I also supply some general guidelines for ripple testing that can be applied to any make or model out there. Engine Performance Diagnostics chapter 1 page 27 Symptoms - speedometer moves off of zero with the vehicle stopped and in gear - check engine light (EGR fault code, unrelated) - transmission shifting problems Fix - replace the alternator (failed rectifier diode) Tests shown - how to check for AC ripple using a lab scope with AC coupling - identifying excessive AC ripple in a sensor voltage waveform - how to eliminate a failed alternator by disconnecting the control circuit - checking AC ripple at the alternator vs. at the battery Tools used - Autel MS908 MaxiSYS Automotive Diagnostic & Analysis System - USA Version https://www.jbtoolsales.com/autel-ms908-maxisys-automotive-diagnostic-analysis-system-usa-version#oid=1014_1 - PicoScope 4425 4 Channel Standard Diagnostic Kit http://www.aeswave.com/cart.php?m=affiliate_go&affiliateID=60df1b5cf6e5582af6ff81c728f42d0d&go=http://www.aeswave.com/PicoScope-4425-4-Channel-Standard-Diagnostic-Kit-p9276.html Playlist - (Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM https://www.youtube.com/playlist?list=PL5E3AEC36DB838BB1 Related videos - How to test an Alternator (alternator not charging from a blown fuse) - Mazda https://youtu.be/--AdY8z1QfU - How to test an alternator (Chrysler Dodge Jeep) https://youtu.be/AvLbb48tQPw - Computer Controlled Alternator Testing - 2006 Mercury https://youtu.be/DHKF6v2QJhc - Battery keeps going dead (what to test before replacing) https://youtu.be/AA-vHbE1IA8 For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book. Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https://www.scannerdanner.com/join-scannerdanner-premium.html There is a 14 day free trial. On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere! Disclaimer: Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.