Intermitttent no start problems from a bad computer ground.
2000 Audi S4 Quattro 2.7 Turbo.

The procedures shown in this video apply to ALL make and model cars. When you understand circuit designs like the 5v reference and sensor ground paths, these types of problems are very easy to identify. The problem on this Audi was revealed within the main sensor circuits (MAP and TPS etc) and was quickly narrowed down to a sensor ground problem.

Engine Performance Diagnostics chapter 1 pages 23-25

symptoms 50

  • random stalling problems
  • intermittent no start
  • clicking noises under the hood when not starting
  • no communication with scan tool
  • throttle body motor clicking rapidly

fix 50

  • tightened loose computer ground eyelet located on the firewall

test shown enh 50

  • electronic throttle body tests
  • throttle position sensor signal tests with a scope
  • MAP sensor signal circuit
  • sensor ground circuit
  • computer ground circuit
  • how to quickly identify a ground circuit problem
  • what is the difference between a sensor ground and computer ground
  • how to check main computer grounds

Tools used

  • scan tool
  • lab scope
  • digital multimeter (may be used instead of a scope)

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ground circuit problems

Related videos:

Poor running, flashing CEL, no codes (Toyota Echo bad computer ground) :


Low Fuel Pressure from a bad fuel pump ground (Ford Ranger) :


MAF sensor trouble code (P0102) caused by a bad ground (Chevy Malibu):


Engine does not crank (Cadillac with a bad block ground):


How to test a starter motor (Nissan no crank from a bad block ground) :


Fuel Pump Relay Problem:


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available 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. 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!